summaryrefslogtreecommitdiffstats
path: root/Documentation/DocBook/v4l/compat.xml
blob: b9dbdf9e6d29bd29b3df3617a77311b947b27e80 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
  <title>Changes</title>

  <para>The following chapters document the evolution of the V4L2 API,
errata or extensions. They are also intended to help application and
driver writers to port or update their code.</para>

  <section id="diff-v4l">
    <title>Differences between V4L and V4L2</title>

    <para>The Video For Linux API was first introduced in Linux 2.1 to
unify and replace various TV and radio device related interfaces,
developed independently by driver writers in prior years. Starting
with Linux 2.5 the much improved V4L2 API replaces the V4L API,
although existing drivers will continue to support V4L applications in
the future, either directly or through the V4L2 compatibility layer in
the <filename>videodev</filename> kernel module translating ioctls on
the fly. For a transition period not all drivers will support the V4L2
API.</para>

    <section>
      <title>Opening and Closing Devices</title>

      <para>For compatibility reasons the character device file names
recommended for V4L2 video capture, overlay, radio, teletext and raw
vbi capture devices did not change from those used by V4L. They are
listed in <xref linkend="devices" /> and below in <xref
	  linkend="v4l-dev" />.</para>

      <para>The V4L <filename>videodev</filename> module automatically
assigns minor numbers to drivers in load order, depending on the
registered device type. We recommend that V4L2 drivers by default
register devices with the same numbers, but the system administrator
can assign arbitrary minor numbers using driver module options. The
major device number remains 81.</para>

      <table id="v4l-dev">
	<title>V4L Device Types, Names and Numbers</title>
	<tgroup cols="3">
	  <thead>
	    <row>
	      <entry>Device Type</entry>
	      <entry>File Name</entry>
	      <entry>Minor Numbers</entry>
	    </row>
	  </thead>
	  <tbody valign="top">
	    <row>
	      <entry>Video capture and overlay</entry>
	      <entry><para><filename>/dev/video</filename> and
<filename>/dev/bttv0</filename><footnote> <para>According to
Documentation/devices.txt these should be symbolic links to
<filename>/dev/video0</filename>. Note the original bttv interface is
not compatible with V4L or V4L2.</para> </footnote>,
<filename>/dev/video0</filename> to
<filename>/dev/video63</filename></para></entry>
	      <entry>0-63</entry>
	    </row>
	    <row>
	      <entry>Radio receiver</entry>
	      <entry><para><filename>/dev/radio</filename><footnote>
		    <para>According to
<filename>Documentation/devices.txt</filename> a symbolic link to
<filename>/dev/radio0</filename>.</para>
		  </footnote>, <filename>/dev/radio0</filename> to
<filename>/dev/radio63</filename></para></entry>
	      <entry>64-127</entry>
	    </row>
	    <row>
	      <entry>Teletext decoder</entry>
	      <entry><para><filename>/dev/vtx</filename>,
<filename>/dev/vtx0</filename> to
<filename>/dev/vtx31</filename></para></entry>
	      <entry>192-223</entry>
	    </row>
	    <row>
	      <entry>Raw VBI capture</entry>
	      <entry><para><filename>/dev/vbi</filename>,
<filename>/dev/vbi0</filename> to
<filename>/dev/vbi31</filename></para></entry>
	      <entry>224-255</entry>
	    </row>
	  </tbody>
	</tgroup>
      </table>

      <para>V4L prohibits (or used to prohibit) multiple opens of a
device file. V4L2 drivers <emphasis>may</emphasis> support multiple
opens, see <xref linkend="open" /> for details and consequences.</para>

      <para>V4L drivers respond to V4L2 ioctls with an &EINVAL;. The
compatibility layer in the V4L2 <filename>videodev</filename> module
can translate V4L ioctl requests to their V4L2 counterpart, however a
V4L2 driver usually needs more preparation to become fully V4L
compatible. This is covered in more detail in <xref
	  linkend="driver" />.</para>
    </section>

    <section>
      <title>Querying Capabilities</title>

      <para>The V4L <constant>VIDIOCGCAP</constant> ioctl is
equivalent to V4L2's &VIDIOC-QUERYCAP;.</para>

      <para>The <structfield>name</structfield> field in struct
<structname>video_capability</structname> became
<structfield>card</structfield> in &v4l2-capability;,
<structfield>type</structfield> was replaced by
<structfield>capabilities</structfield>. Note V4L2 does not
distinguish between device types like this, better think of basic
video input, video output and radio devices supporting a set of
related functions like video capturing, video overlay and VBI
capturing. See <xref linkend="open" /> for an
introduction.<informaltable>
	  <tgroup cols="3">
	    <thead>
	      <row>
		<entry>struct
<structname>video_capability</structname>
<structfield>type</structfield></entry>
		<entry>&v4l2-capability;
<structfield>capabilities</structfield> flags</entry>
		<entry>Purpose</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry><constant>VID_TYPE_CAPTURE</constant></entry>
		<entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
		<entry>The <link linkend="capture">video
capture</link> interface is supported.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_TUNER</constant></entry>
		<entry><constant>V4L2_CAP_TUNER</constant></entry>
		<entry>The device has a <link linkend="tuner">tuner or
modulator</link>.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_TELETEXT</constant></entry>
		<entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
		<entry>The <link linkend="raw-vbi">raw VBI
capture</link> interface is supported.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_OVERLAY</constant></entry>
		<entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
		<entry>The <link linkend="overlay">video
overlay</link> interface is supported.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_CHROMAKEY</constant></entry>
		<entry><constant>V4L2_FBUF_CAP_CHROMAKEY</constant> in
field <structfield>capability</structfield> of
&v4l2-framebuffer;</entry>
		<entry>Whether chromakey overlay is supported. For
more information on overlay see
<xref linkend="overlay" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_CLIPPING</constant></entry>
		<entry><constant>V4L2_FBUF_CAP_LIST_CLIPPING</constant>
and <constant>V4L2_FBUF_CAP_BITMAP_CLIPPING</constant> in field
<structfield>capability</structfield> of &v4l2-framebuffer;</entry>
		<entry>Whether clipping the overlaid image is
supported, see <xref linkend="overlay" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_FRAMERAM</constant></entry>
		<entry><constant>V4L2_FBUF_CAP_EXTERNOVERLAY</constant>
<emphasis>not set</emphasis> in field
<structfield>capability</structfield> of &v4l2-framebuffer;</entry>
		<entry>Whether overlay overwrites frame buffer memory,
see <xref linkend="overlay" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_SCALES</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>This flag indicates if the hardware can scale
images. The V4L2 API implies the scale factor by setting the cropping
dimensions and image size with the &VIDIOC-S-CROP; and &VIDIOC-S-FMT;
ioctl, respectively. The driver returns the closest sizes possible.
For more information on cropping and scaling see <xref
		    linkend="crop" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_MONOCHROME</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>Applications can enumerate the supported image
formats with the &VIDIOC-ENUM-FMT; ioctl to determine if the device
supports grey scale capturing only. For more information on image
formats see <xref linkend="pixfmt" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_SUBCAPTURE</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>Applications can call the &VIDIOC-G-CROP; ioctl
to determine if the device supports capturing a subsection of the full
picture ("cropping" in V4L2). If not, the ioctl returns the &EINVAL;.
For more information on cropping and scaling see <xref
		    linkend="crop" />.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_MPEG_DECODER</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>Applications can enumerate the supported image
formats with the &VIDIOC-ENUM-FMT; ioctl to determine if the device
supports MPEG streams.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_MPEG_ENCODER</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>See above.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_MJPEG_DECODER</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>See above.</entry>
	      </row>
	      <row>
		<entry><constant>VID_TYPE_MJPEG_ENCODER</constant></entry>
		<entry><constant>-</constant></entry>
		<entry>See above.</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable></para>

      <para>The <structfield>audios</structfield> field was replaced
by <structfield>capabilities</structfield> flag
<constant>V4L2_CAP_AUDIO</constant>, indicating
<emphasis>if</emphasis> the device has any audio inputs or outputs. To
determine their number applications can enumerate audio inputs with
the &VIDIOC-G-AUDIO; ioctl. The audio ioctls are described in <xref
	  linkend="audio" />.</para>

      <para>The <structfield>maxwidth</structfield>,
<structfield>maxheight</structfield>,
<structfield>minwidth</structfield> and
<structfield>minheight</structfield> fields were removed. Calling the
&VIDIOC-S-FMT; or &VIDIOC-TRY-FMT; ioctl with the desired dimensions
returns the closest size possible, taking into account the current
video standard, cropping and scaling limitations.</para>
    </section>

    <section>
      <title>Video Sources</title>

      <para>V4L provides the <constant>VIDIOCGCHAN</constant> and
<constant>VIDIOCSCHAN</constant> ioctl using struct
<structname>video_channel</structname> to enumerate
the video inputs of a V4L device. The equivalent V4L2 ioctls
are &VIDIOC-ENUMINPUT;, &VIDIOC-G-INPUT; and &VIDIOC-S-INPUT;
using &v4l2-input; as discussed in <xref linkend="video" />.</para>

      <para>The <structfield>channel</structfield> field counting
inputs was renamed to <structfield>index</structfield>, the video
input types were renamed as follows: <informaltable>
	  <tgroup cols="2">
	    <thead>
	      <row>
		<entry>struct <structname>video_channel</structname>
<structfield>type</structfield></entry>
		<entry>&v4l2-input;
<structfield>type</structfield></entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry><constant>VIDEO_TYPE_TV</constant></entry>
		<entry><constant>V4L2_INPUT_TYPE_TUNER</constant></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_TYPE_CAMERA</constant></entry>
		<entry><constant>V4L2_INPUT_TYPE_CAMERA</constant></entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable></para>

      <para>Unlike the <structfield>tuners</structfield> field
expressing the number of tuners of this input, V4L2 assumes each video
input is connected to at most one tuner. However a tuner can have more
than one input, &ie; RF connectors, and a device can have multiple
tuners. The index number of the tuner associated with the input, if
any, is stored in field <structfield>tuner</structfield> of
&v4l2-input;. Enumeration of tuners is discussed in <xref
	  linkend="tuner" />.</para>

      <para>The redundant <constant>VIDEO_VC_TUNER</constant> flag was
dropped. Video inputs associated with a tuner are of type
<constant>V4L2_INPUT_TYPE_TUNER</constant>. The
<constant>VIDEO_VC_AUDIO</constant> flag was replaced by the
<structfield>audioset</structfield> field. V4L2 considers devices with
up to 32 audio inputs. Each set bit in the
<structfield>audioset</structfield> field represents one audio input
this video input combines with. For information about audio inputs and
how to switch between them see <xref linkend="audio" />.</para>

      <para>The <structfield>norm</structfield> field describing the
supported video standards was replaced by
<structfield>std</structfield>. The V4L specification mentions a flag
<constant>VIDEO_VC_NORM</constant> indicating whether the standard can
be changed. This flag was a later addition together with the
<structfield>norm</structfield> field and has been removed in the
meantime. V4L2 has a similar, albeit more comprehensive approach
to video standards, see <xref linkend="standard" /> for more
information.</para>
    </section>

    <section>
      <title>Tuning</title>

      <para>The V4L <constant>VIDIOCGTUNER</constant> and
<constant>VIDIOCSTUNER</constant> ioctl and struct
<structname>video_tuner</structname> can be used to enumerate the
tuners of a V4L TV or radio device. The equivalent V4L2 ioctls are
&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; using &v4l2-tuner;. Tuners are
covered in <xref linkend="tuner" />.</para>

      <para>The <structfield>tuner</structfield> field counting tuners
was renamed to <structfield>index</structfield>. The fields
<structfield>name</structfield>, <structfield>rangelow</structfield>
and <structfield>rangehigh</structfield> remained unchanged.</para>

      <para>The <constant>VIDEO_TUNER_PAL</constant>,
<constant>VIDEO_TUNER_NTSC</constant> and
<constant>VIDEO_TUNER_SECAM</constant> flags indicating the supported
video standards were dropped. This information is now contained in the
associated &v4l2-input;. No replacement exists for the
<constant>VIDEO_TUNER_NORM</constant> flag indicating whether the
video standard can be switched. The <structfield>mode</structfield>
field to select a different video standard was replaced by a whole new
set of ioctls and structures described in <xref linkend="standard" />.
Due to its ubiquity it should be mentioned the BTTV driver supports
several standards in addition to the regular
<constant>VIDEO_MODE_PAL</constant> (0),
<constant>VIDEO_MODE_NTSC</constant>,
<constant>VIDEO_MODE_SECAM</constant> and
<constant>VIDEO_MODE_AUTO</constant> (3). Namely N/PAL Argentina,
M/PAL, N/PAL, and NTSC Japan with numbers 3-6 (sic).</para>

      <para>The <constant>VIDEO_TUNER_STEREO_ON</constant> flag
indicating stereo reception became
<constant>V4L2_TUNER_SUB_STEREO</constant> in field
<structfield>rxsubchans</structfield>. This field also permits the
detection of monaural and bilingual audio, see the definition of
&v4l2-tuner; for details. Presently no replacement exists for the
<constant>VIDEO_TUNER_RDS_ON</constant> and
<constant>VIDEO_TUNER_MBS_ON</constant> flags.</para>

      <para> The <constant>VIDEO_TUNER_LOW</constant> flag was renamed
to <constant>V4L2_TUNER_CAP_LOW</constant> in the &v4l2-tuner;
<structfield>capability</structfield> field.</para>

      <para>The <constant>VIDIOCGFREQ</constant> and
<constant>VIDIOCSFREQ</constant> ioctl to change the tuner frequency
where renamed to &VIDIOC-G-FREQUENCY; and  &VIDIOC-S-FREQUENCY;. They
take a pointer to a &v4l2-frequency; instead of an unsigned long
integer.</para>
    </section>

    <section id="v4l-image-properties">
      <title>Image Properties</title>

      <para>V4L2 has no equivalent of the
<constant>VIDIOCGPICT</constant> and <constant>VIDIOCSPICT</constant>
ioctl and struct <structname>video_picture</structname>. The following
fields where replaced by V4L2 controls accessible with the
&VIDIOC-QUERYCTRL;, &VIDIOC-G-CTRL; and &VIDIOC-S-CTRL; ioctls:<informaltable>
	  <tgroup cols="2">
	    <thead>
	      <row>
		<entry>struct <structname>video_picture</structname></entry>
		<entry>V4L2 Control ID</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry><structfield>brightness</structfield></entry>
		<entry><constant>V4L2_CID_BRIGHTNESS</constant></entry>
	      </row>
	      <row>
		<entry><structfield>hue</structfield></entry>
		<entry><constant>V4L2_CID_HUE</constant></entry>
	      </row>
	      <row>
		<entry><structfield>colour</structfield></entry>
		<entry><constant>V4L2_CID_SATURATION</constant></entry>
	      </row>
	      <row>
		<entry><structfield>contrast</structfield></entry>
		<entry><constant>V4L2_CID_CONTRAST</constant></entry>
	      </row>
	      <row>
		<entry><structfield>whiteness</structfield></entry>
		<entry><constant>V4L2_CID_WHITENESS</constant></entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable></para>

      <para>The V4L picture controls are assumed to range from 0 to
65535 with no particular reset value. The V4L2 API permits arbitrary
limits and defaults which can be queried with the &VIDIOC-QUERYCTRL;
ioctl. For general information about controls see <xref
linkend="control" />.</para>

      <para>The <structfield>depth</structfield> (average number of
bits per pixel) of a video image is implied by the selected image
format. V4L2 does not explicitely provide such information assuming
applications recognizing the format are aware of the image depth and
others need not know. The <structfield>palette</structfield> field
moved into the &v4l2-pix-format;:<informaltable>
	  <tgroup cols="2">
	    <thead>
	      <row>
		<entry>struct <structname>video_picture</structname>
<structfield>palette</structfield></entry>
		<entry>&v4l2-pix-format;
<structfield>pixfmt</structfield></entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry><constant>VIDEO_PALETTE_GREY</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-GREY"><constant>V4L2_PIX_FMT_GREY</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_HI240</constant></entry>
		<entry><para><link
linkend="pixfmt-reserved"><constant>V4L2_PIX_FMT_HI240</constant></link><footnote>
		      <para>This is a custom format used by the BTTV
driver, not one of the V4L2 standard formats.</para>
		    </footnote></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_RGB565</constant></entry>
		<entry><para><link
linkend="pixfmt-rgb"><constant>V4L2_PIX_FMT_RGB565</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_RGB555</constant></entry>
		<entry><para><link
linkend="pixfmt-rgb"><constant>V4L2_PIX_FMT_RGB555</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_RGB24</constant></entry>
		<entry><para><link
linkend="pixfmt-rgb"><constant>V4L2_PIX_FMT_BGR24</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_RGB32</constant></entry>
		<entry><para><link
linkend="pixfmt-rgb"><constant>V4L2_PIX_FMT_BGR32</constant></link><footnote>
		      <para>Presumably all V4L RGB formats are
little-endian, although some drivers might interpret them according to machine endianess. V4L2 defines little-endian, big-endian and red/blue
swapped variants. For details see <xref linkend="pixfmt-rgb" />.</para>
		    </footnote></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV422</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YUYV"><constant>V4L2_PIX_FMT_YUYV</constant></link></para></entry>
	      </row>
	      <row>
		<entry><para><constant>VIDEO_PALETTE_YUYV</constant><footnote>
		      <para><constant>VIDEO_PALETTE_YUV422</constant>
and <constant>VIDEO_PALETTE_YUYV</constant> are the same formats. Some
V4L drivers respond to one, some to the other.</para>
		    </footnote></para></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YUYV"><constant>V4L2_PIX_FMT_YUYV</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_UYVY</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-UYVY"><constant>V4L2_PIX_FMT_UYVY</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV420</constant></entry>
		<entry>None</entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV411</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-Y41P"><constant>V4L2_PIX_FMT_Y41P</constant></link><footnote>
		      <para>Not to be confused with
<constant>V4L2_PIX_FMT_YUV411P</constant>, which is a planar
format.</para> </footnote></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_RAW</constant></entry>
		<entry><para>None<footnote> <para>V4L explains this
as: "RAW capture (BT848)"</para> </footnote></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV422P</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YUV422P"><constant>V4L2_PIX_FMT_YUV422P</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV411P</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YUV411P"><constant>V4L2_PIX_FMT_YUV411P</constant></link><footnote>
		      <para>Not to be confused with
<constant>V4L2_PIX_FMT_Y41P</constant>, which is a packed
format.</para> </footnote></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV420P</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YVU420"><constant>V4L2_PIX_FMT_YVU420</constant></link></para></entry>
	      </row>
	      <row>
		<entry><constant>VIDEO_PALETTE_YUV410P</constant></entry>
		<entry><para><link
linkend="V4L2-PIX-FMT-YVU410"><constant>V4L2_PIX_FMT_YVU410</constant></link></para></entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable></para>

      <para>V4L2 image formats are defined in <xref
linkend="pixfmt" />. The image format can be selected with the
&VIDIOC-S-FMT; ioctl.</para>
    </section>

    <section>
      <title>Audio</title>

      <para>The <constant>VIDIOCGAUDIO</constant> and
<constant>VIDIOCSAUDIO</constant> ioctl and struct
<structname>video_audio</structname> are used to enumerate the
audio inputs of a V4L device. The equivalent V4L2 ioctls are
&VIDIOC-G-AUDIO; and &VIDIOC-S-AUDIO; using &v4l2-audio; as
discussed in <xref linkend="audio" />.</para>

      <para>The <structfield>audio</structfield> "channel number"
field counting audio inputs was renamed to
<structfield>index</structfield>.</para>

      <para>On <constant>VIDIOCSAUDIO</constant> the
<structfield>mode</structfield> field selects <emphasis>one</emphasis>
of the <constant>VIDEO_SOUND_MONO</constant>,
<constant>VIDEO_SOUND_STEREO</constant>,
<constant>VIDEO_SOUND_LANG1</constant> or
<constant>VIDEO_SOUND_LANG2</constant> audio demodulation modes. When
the current audio standard is BTSC
<constant>VIDEO_SOUND_LANG2</constant> refers to SAP and
<constant>VIDEO_SOUND_LANG1</constant> is meaningless. Also
undocumented in the V4L specification, there is no way to query the
selected mode. On <constant>VIDIOCGAUDIO</constant> the driver returns
the <emphasis>actually received</emphasis> audio programmes in this
field. In the V4L2 API this information is stored in the &v4l2-tuner;
<structfield>rxsubchans</structfield> and
<structfield>audmode</structfield> fields, respectively. See <xref
linkend="tuner" /> for more information on tuners. Related to audio
modes &v4l2-audio; also reports if this is a mono or stereo
input, regardless if the source is a tuner.</para>

      <para>The following fields where replaced by V4L2 controls
accessible with the &VIDIOC-QUERYCTRL;, &VIDIOC-G-CTRL; and
&VIDIOC-S-CTRL; ioctls:<informaltable>
	  <tgroup cols="2">
	    <thead>
	      <row>
		<entry>struct
<structname>video_audio</structname></entry>
		<entry>V4L2 Control ID</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry><structfield>volume</structfield></entry>
		<entry><constant>V4L2_CID_AUDIO_VOLUME</constant></entry>
	      </row>
	      <row>
		<entry><structfield>bass</structfield></entry>
		<entry><constant>V4L2_CID_AUDIO_BASS</constant></entry>
	      </row>
	      <row>
		<entry><structfield>treble</structfield></entry>
		<entry><constant>V4L2_CID_AUDIO_TREBLE</constant></entry>
	      </row>
	      <row>
		<entry><structfield>balance</structfield></entry>
		<entry><constant>V4L2_CID_AUDIO_BALANCE</constant></entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable></para>

      <para>To determine which of these controls are supported by a
driver V4L provides the <structfield>flags</structfield>
<constant>VIDEO_AUDIO_VOLUME</constant>,
<constant>VIDEO_AUDIO_BASS</constant>,
<constant>VIDEO_AUDIO_TREBLE</constant> and
<constant>VIDEO_AUDIO_BALANCE</constant>. In the V4L2 API the
&VIDIOC-QUERYCTRL; ioctl reports if the respective control is
supported. Accordingly the <constant>VIDEO_AUDIO_MUTABLE</constant>
and <constant>VIDEO_AUDIO_MUTE</constant> flags where replaced by the
boolean <constant>V4L2_CID_AUDIO_MUTE</constant> control.</para>

      <para>All V4L2 controls have a <structfield>step</structfield>
attribute replacing the struct <structname>video_audio</structname>
<structfield>step</structfield> field. The V4L audio controls are
assumed to range from 0 to 65535 with no particular reset value. The
V4L2 API permits arbitrary limits and defaults which can be queried
with the &VIDIOC-QUERYCTRL; ioctl. For general information about
controls see <xref linkend="control" />.</para>
    </section>

    <section>
      <title>Frame Buffer Overlay</title>

      <para>The V4L2 ioctls equivalent to
<constant>VIDIOCGFBUF</constant> and <constant>VIDIOCSFBUF</constant>
are &VIDIOC-G-FBUF; and &VIDIOC-S-FBUF;. The
<structfield>base</structfield> field of struct
<structname>video_buffer</structname> remained unchanged, except V4L2
defines a flag to indicate non-destructive overlays instead of a
<constant>NULL</constant> pointer. All other fields moved into the
&v4l2-pix-format; <structfield>fmt</structfield> substructure of
&v4l2-framebuffer;. The <structfield>depth</structfield> field was
replaced by <structfield>pixelformat</structfield>. See <xref
	  linkend="pixfmt-rgb" /> for a list of RGB formats and their
respective color depths.</para>

      <para>Instead of the special ioctls
<constant>VIDIOCGWIN</constant> and <constant>VIDIOCSWIN</constant>
V4L2 uses the general-purpose data format negotiation ioctls
&VIDIOC-G-FMT; and &VIDIOC-S-FMT;. They take a pointer to a
&v4l2-format; as argument. Here the <structfield>win</structfield>
member of the <structfield>fmt</structfield> union is used, a
&v4l2-window;.</para>

      <para>The <structfield>x</structfield>,
<structfield>y</structfield>, <structfield>width</structfield> and
<structfield>height</structfield> fields of struct
<structname>video_window</structname> moved into &v4l2-rect;
substructure <structfield>w</structfield> of struct
<structname>v4l2_window</structname>. The
<structfield>chromakey</structfield>,
<structfield>clips</structfield>, and
<structfield>clipcount</structfield> fields remained unchanged. Struct
<structname>video_clip</structname> was renamed to &v4l2-clip;, also
containing a struct <structname>v4l2_rect</structname>, but the
semantics are still the same.</para>

      <para>The <constant>VIDEO_WINDOW_INTERLACE</constant> flag was
dropped. Instead applications must set the
<structfield>field</structfield> field to
<constant>V4L2_FIELD_ANY</constant> or
<constant>V4L2_FIELD_INTERLACED</constant>. The
<constant>VIDEO_WINDOW_CHROMAKEY</constant> flag moved into
&v4l2-framebuffer;, under the new name
<constant>V4L2_FBUF_FLAG_CHROMAKEY</constant>.</para>

      <para>In V4L, storing a bitmap pointer in
<structfield>clips</structfield> and setting
<structfield>clipcount</structfield> to
<constant>VIDEO_CLIP_BITMAP</constant> (-1) requests bitmap
clipping, using a fixed size bitmap of 1024 &times; 625 bits. Struct
<structname>v4l2_window</structname> has a separate
<structfield>bitmap</structfield> pointer field for this purpose and
the bitmap size is determined by <structfield>w.width</structfield> and
<structfield>w.height</structfield>.</para>

      <para>The <constant>VIDIOCCAPTURE</constant> ioctl to enable or
disable overlay was renamed to &VIDIOC-OVERLAY;.</para>
    </section>

    <section>
      <title>Cropping</title>

      <para>To capture only a subsection of the full picture V4L
defines the <constant>VIDIOCGCAPTURE</constant> and
<constant>VIDIOCSCAPTURE</constant> ioctls using struct
<structname>video_capture</structname>. The equivalent V4L2 ioctls are
&VIDIOC-G-CROP; and &VIDIOC-S-CROP; using &v4l2-crop;, and the related
&VIDIOC-CROPCAP; ioctl. This is a rather complex matter, see
<xref linkend="crop" /> for details.</para>

      <para>The <structfield>x</structfield>,
<structfield>y</structfield>, <structfield>width</structfield> and
<structfield>height</structfield> fields moved into &v4l2-rect;
substructure <structfield>c</structfield> of struct
<structname>v4l2_crop</structname>. The
<structfield>decimation</structfield> field was dropped. In the V4L2
API the scaling factor is implied by the size of the cropping
rectangle and the size of the captured or overlaid image.</para>

      <para>The <constant>VIDEO_CAPTURE_ODD</constant>
and <constant>VIDEO_CAPTURE_EVEN</constant> flags to capture only the
odd or even field, respectively, were replaced by
<constant>V4L2_FIELD_TOP</constant> and
<constant>V4L2_FIELD_BOTTOM</constant> in the field named
<structfield>field</structfield> of &v4l2-pix-format; and
&v4l2-window;. These structures are used to select a capture or
overlay format with the &VIDIOC-S-FMT; ioctl.</para>
    </section>

    <section>
      <title>Reading Images, Memory Mapping</title>

      <section>
	<title>Capturing using the read method</title>

	<para>There is no essential difference between reading images
from a V4L or V4L2 device using the &func-read; function, however V4L2
drivers are not required to support this I/O method. Applications can
determine if the function is available with the &VIDIOC-QUERYCAP;
ioctl. All V4L2 devices exchanging data with applications must support
the &func-select; and &func-poll; functions.</para>

	<para>To select an image format and size, V4L provides the
<constant>VIDIOCSPICT</constant> and <constant>VIDIOCSWIN</constant>
ioctls. V4L2 uses the general-purpose data format negotiation ioctls
&VIDIOC-G-FMT; and &VIDIOC-S-FMT;. They take a pointer to a
&v4l2-format; as argument, here the &v4l2-pix-format; named
<structfield>pix</structfield> of its <structfield>fmt</structfield>
union is used.</para>

	<para>For more information about the V4L2 read interface see
<xref linkend="rw" />.</para>
      </section>
      <section>
	<title>Capturing using memory mapping</title>

	<para>Applications can read from V4L devices by mapping
buffers in device memory, or more often just buffers allocated in
DMA-able system memory, into their address space. This avoids the data
copying overhead of the read method. V4L2 supports memory mapping as
well, with a few differences.</para>

	<informaltable>
	  <tgroup cols="2">
	    <thead>
	      <row>
		<entry>V4L</entry>
		<entry>V4L2</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row>
		<entry></entry>
		<entry>The image format must be selected before
buffers are allocated, with the &VIDIOC-S-FMT; ioctl. When no format
is selected the driver may use the last, possibly by another
application requested format.</entry>
	      </row>
	      <row>
		<entry><para>Applications cannot change the number of
buffers. The it is built into the driver, unless it has a module
option to change the number when the driver module is
loaded.</para></entry>
		<entry><para>The &VIDIOC-REQBUFS; ioctl allocates the
desired number of buffers, this is a required step in the initialization
sequence.</para></entry>
	      </row>
	      <row>
		<entry><para>Drivers map all buffers as one contiguous
range of memory. The <constant>VIDIOCGMBUF</constant> ioctl is
available to query the number of buffers, the offset of each buffer
from the start of the virtual file, and the overall amount of memory
used, which can be used as arguments for the &func-mmap;
function.</para></entry>
		<entry><para>Buffers are individually mapped. The
offset and size of each buffer can be determined with the
&VIDIOC-QUERYBUF; ioctl.</para></entry>
	      </row>
	      <row>
		<entry><para>The <constant>VIDIOCMCAPTURE</constant>
ioctl prepares a buffer for capturing. It also determines the image
format for this buffer. The ioctl returns immediately, eventually with
an &EAGAIN; if no video signal had been detected. When the driver
supports more than one buffer applications can call the ioctl multiple
times and thus have multiple outstanding capture
requests.</para><para>The <constant>VIDIOCSYNC</constant> ioctl
suspends execution until a particular buffer has been
filled.</para></entry>
		<entry><para>Drivers maintain an incoming and outgoing
queue. &VIDIOC-QBUF; enqueues any empty buffer into the incoming
queue. Filled buffers are dequeued from the outgoing queue with the
&VIDIOC-DQBUF; ioctl. To wait until filled buffers become available this
function, &func-select; or &func-poll; can be used. The
&VIDIOC-STREAMON; ioctl must be called once after enqueuing one or
more buffers to start capturing. Its counterpart
&VIDIOC-STREAMOFF; stops capturing and dequeues all buffers from both
queues. Applications can query the signal status, if known, with the
&VIDIOC-ENUMINPUT; ioctl.</para></entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>

	<para>For a more in-depth discussion of memory mapping and
examples, see <xref linkend="mmap" />.</para>
      </section>
    </section>

    <section>
      <title>Reading Raw VBI Data</title>

      <para>Originally the V4L API did not specify a raw VBI capture
interface, only the device file <filename>/dev/vbi</filename> was
reserved for this purpose. The only driver supporting this interface
was the BTTV driver, de-facto defining the V4L VBI interface. Reading
from the device yields a raw VBI image with the following
parameters:<informaltable>
	    <tgroup cols="2">
	      <thead>
		<row>
		  <entry>&v4l2-vbi-format;</entry>
		  <entry>V4L, BTTV driver</entry>
		</row>
	      </thead>
	      <tbody valign="top">
		<row>
		  <entry>sampling_rate</entry>
		  <entry>28636363&nbsp;Hz NTSC (or any other 525-line
standard); 35468950&nbsp;Hz PAL and SECAM (625-line standards)</entry>
		</row>
		<row>
		  <entry>offset</entry>
		  <entry>?</entry>
		</row>
		<row>
		  <entry>samples_per_line</entry>
		  <entry>2048</entry>
		</row>
		<row>
		  <entry>sample_format</entry>
		  <entry>V4L2_PIX_FMT_GREY. The last four bytes (a
machine endianess integer) contain a frame counter.</entry>
		</row>
		<row>
		  <entry>start[]</entry>
		  <entry>10, 273 NTSC; 22, 335 PAL and SECAM</entry>
		</row>
		<row>
		  <entry>count[]</entry>
		  <entry><para>16, 16<footnote><para>Old driver
versions used different values, eventually the custom
<constant>BTTV_VBISIZE</constant> ioctl was added to query the
correct values.</para></footnote></para></entry>
		</row>
		<row>
		  <entry>flags</entry>
		  <entry>0</entry>
		</row>
	      </tbody>
	    </tgroup>
	</informaltable></para>

      <para>Undocumented in the V4L specification, in Linux 2.3 the
<constant>VIDIOCGVBIFMT</constant> and
<constant>VIDIOCSVBIFMT</constant> ioctls using struct
<structname>vbi_format</structname> were added to determine the VBI
image parameters. These ioctls are only partially compatible with the
V4L2 VBI interface specified in <xref linkend="raw-vbi" />.</para>

      <para>An <structfield>offset</structfield> field does not
exist, <structfield>sample_format</structfield> is supposed to be
<constant>VIDEO_PALETTE_RAW</constant>, equivalent to
<constant>V4L2_PIX_FMT_GREY</constant>. The remaining fields are
probably equivalent to &v4l2-vbi-format;.</para>

      <para>Apparently only the Zoran (ZR 36120) driver implements
these ioctls. The semantics differ from those specified for V4L2 in two
ways. The parameters are reset on &func-open; and
<constant>VIDIOCSVBIFMT</constant> always returns an &EINVAL; if the
parameters are invalid.</para>
    </section>

    <section>
      <title>Miscellaneous</title>

      <para>V4L2 has no equivalent of the
<constant>VIDIOCGUNIT</constant> ioctl. Applications can find the VBI
device associated with a video capture device (or vice versa) by
reopening the device and requesting VBI data. For details see
<xref linkend="open" />.</para>

      <para>No replacement exists for <constant>VIDIOCKEY</constant>,
and the V4L functions for microcode programming. A new interface for
MPEG compression and playback devices is documented in <xref
	  linkend="extended-controls" />.</para>
    </section>

  </section>

  <section id="hist-v4l2">
    <title>Changes of the V4L2 API</title>

    <para>Soon after the V4L API was added to the kernel it was
criticised as too inflexible. In August 1998 Bill Dirks proposed a
number of improvements and began to work on documentation, example
drivers and applications. With the help of other volunteers this
eventually became the V4L2 API, not just an extension but a
replacement for the V4L API. However it took another four years and
two stable kernel releases until the new API was finally accepted for
inclusion into the kernel in its present form.</para>

    <section>
      <title>Early Versions</title>
      <para>1998-08-20: First version.</para>

      <para>1998-08-27: The &func-select; function was introduced.</para>

      <para>1998-09-10: New video standard interface.</para>

      <para>1998-09-18: The <constant>VIDIOC_NONCAP</constant> ioctl
was replaced by the otherwise meaningless <constant>O_TRUNC</constant>
&func-open; flag, and the aliases <constant>O_NONCAP</constant> and
<constant>O_NOIO</constant> were defined. Applications can set this
flag if they intend to access controls only, as opposed to capture
applications which need exclusive access. The
<constant>VIDEO_STD_XXX</constant> identifiers are now ordinals
instead of flags, and the <function>video_std_construct()</function>
helper function takes id and transmission arguments.</para>

      <para>1998-09-28: Revamped video standard. Made video controls
individually enumerable.</para>

      <para>1998-10-02: The <structfield>id</structfield> field was
removed from struct <structname>video_standard</structname> and the
color subcarrier fields were renamed. The &VIDIOC-QUERYSTD; ioctl was
renamed to &VIDIOC-ENUMSTD;, &VIDIOC-G-INPUT; to &VIDIOC-ENUMINPUT;. A
first draft of the Codec API was released.</para>

      <para>1998-11-08: Many minor changes. Most symbols have been
renamed. Some material changes to &v4l2-capability;.</para>

      <para>1998-11-12: The read/write directon of some ioctls was misdefined.</para>

      <para>1998-11-14: <constant>V4L2_PIX_FMT_RGB24</constant>
changed to <constant>V4L2_PIX_FMT_BGR24</constant>, and
<constant>V4L2_PIX_FMT_RGB32</constant> changed to
<constant>V4L2_PIX_FMT_BGR32</constant>. Audio controls are now
accessible with the &VIDIOC-G-CTRL; and &VIDIOC-S-CTRL; ioctls under
names starting with <constant>V4L2_CID_AUDIO</constant>. The
<constant>V4L2_MAJOR</constant> define was removed from
<filename>videodev.h</filename> since it was only used once in the
<filename>videodev</filename> kernel module. The
<constant>YUV422</constant> and <constant>YUV411</constant> planar
image formats were added.</para>

      <para>1998-11-28: A few ioctl symbols changed. Interfaces for codecs and
video output devices were added.</para>

      <para>1999-01-14: A raw VBI capture interface was added.</para>

      <para>1999-01-19: The <constant>VIDIOC_NEXTBUF</constant> ioctl
      was removed.</para>
    </section>

    <section>
      <title>V4L2 Version 0.16 1999-01-31</title>
      <para>1999-01-27: There is now one QBUF ioctl, VIDIOC_QWBUF and VIDIOC_QRBUF
are gone. VIDIOC_QBUF takes a v4l2_buffer as a parameter. Added
digital zoom (cropping) controls.</para>
    </section>

    <!-- Where's 0.17? mhs couldn't find that videodev.h, perhaps Bill
	 forgot to bump the version number or never released it. -->

    <section>
      <title>V4L2 Version 0.18 1999-03-16</title>
      <para>Added a v4l to V4L2 ioctl compatibility layer to
videodev.c. Driver writers, this changes how you implement your ioctl
handler. See the Driver Writer's Guide. Added some more control id
codes.</para>
    </section>

    <section>
      <title>V4L2 Version 0.19 1999-06-05</title>
      <para>1999-03-18: Fill in the category and catname fields of
v4l2_queryctrl objects before passing them to the driver. Required a
minor change to the VIDIOC_QUERYCTRL handlers in the sample
drivers.</para>
      <para>1999-03-31: Better compatibility for v4l memory capture
ioctls. Requires changes to drivers to fully support new compatibility
features, see Driver Writer's Guide and v4l2cap.c. Added new control
IDs: V4L2_CID_HFLIP, _VFLIP. Changed V4L2_PIX_FMT_YUV422P to _YUV422P,
and _YUV411P to _YUV411P.</para>
      <para>1999-04-04: Added a few more control IDs.</para>
      <para>1999-04-07: Added the button control type.</para>
      <para>1999-05-02: Fixed a typo in videodev.h, and added the
V4L2_CTRL_FLAG_GRAYED (later V4L2_CTRL_FLAG_GRABBED) flag.</para>
      <para>1999-05-20: Definition of VIDIOC_G_CTRL was wrong causing
a malfunction of this ioctl.</para>
      <para>1999-06-05: Changed the value of
V4L2_CID_WHITENESS.</para>
    </section>

    <section>
      <title>V4L2 Version 0.20 (1999-09-10)</title>

      <para>Version 0.20 introduced a number of changes which were
<emphasis>not backward compatible</emphasis> with 0.19 and earlier
versions. Purpose of these changes was to simplify the API, while
making it more extensible and following common Linux driver API
conventions.</para>

      <orderedlist>
	<listitem>
	  <para>Some typos in <constant>V4L2_FMT_FLAG</constant>
symbols were fixed. &v4l2-clip; was changed for compatibility with
v4l. (1999-08-30)</para>
	</listitem>

	<listitem>
	  <para><constant>V4L2_TUNER_SUB_LANG1</constant> was added.
(1999-09-05)</para>
	</listitem>

	<listitem>
	  <para>All ioctl() commands that used an integer argument now
take a pointer to an integer. Where it makes sense, ioctls will return
the actual new value in the integer pointed to by the argument, a
common convention in the V4L2 API. The affected ioctls are:
VIDIOC_PREVIEW, VIDIOC_STREAMON, VIDIOC_STREAMOFF, VIDIOC_S_FREQ,
VIDIOC_S_INPUT, VIDIOC_S_OUTPUT, VIDIOC_S_EFFECT. For example
<programlisting>
err = ioctl (fd, VIDIOC_XXX, V4L2_XXX);
</programlisting> becomes <programlisting>
int a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &amp;a);
</programlisting>
	  </para>
	</listitem>

	<listitem>
	  <para>All the different get- and set-format commands were
swept into one &VIDIOC-G-FMT; and &VIDIOC-S-FMT; ioctl taking a union
and a type field selecting the union member as parameter. Purpose is to
simplify the API by eliminating several ioctls and to allow new and
driver private data streams without adding new ioctls.</para>

	  <para>This change obsoletes the following ioctls:
<constant>VIDIOC_S_INFMT</constant>,
<constant>VIDIOC_G_INFMT</constant>,
<constant>VIDIOC_S_OUTFMT</constant>,
<constant>VIDIOC_G_OUTFMT</constant>,
<constant>VIDIOC_S_VBIFMT</constant> and
<constant>VIDIOC_G_VBIFMT</constant>. The image format structure
<structname>v4l2_format</structname> was renamed to &v4l2-pix-format;,
while &v4l2-format; is now the envelopping structure for all format
negotiations.</para>
	</listitem>

	<listitem>
	  <para>Similar to the changes above, the
<constant>VIDIOC_G_PARM</constant> and
<constant>VIDIOC_S_PARM</constant> ioctls were merged with
<constant>VIDIOC_G_OUTPARM</constant> and
<constant>VIDIOC_S_OUTPARM</constant>. A
<structfield>type</structfield> field in the new &v4l2-streamparm;
selects the respective union member.</para>

	  <para>This change obsoletes the
<constant>VIDIOC_G_OUTPARM</constant> and
<constant>VIDIOC_S_OUTPARM</constant> ioctls.</para>
	</listitem>

	<listitem>
	  <para>Control enumeration was simplified, and two new
control flags were introduced and one dropped. The
<structfield>catname</structfield> field was replaced by a
<structfield>group</structfield> field.</para>

	  <para>Drivers can now flag unsupported and temporarily
unavailable controls with <constant>V4L2_CTRL_FLAG_DISABLED</constant>
and <constant>V4L2_CTRL_FLAG_GRABBED</constant> respectively. The
<structfield>group</structfield> name indicates a possibly narrower
classification than the <structfield>category</structfield>. In other
words, there may be multiple groups within a category. Controls within
a group would typically be drawn within a group box. Controls in
different categories might have a greater separation, or may even
appear in separate windows.</para>
	</listitem>

	<listitem>
	  <para>The &v4l2-buffer; <structfield>timestamp</structfield>
was changed to a 64 bit integer, containing the sampling or output
time of the frame in nanoseconds. Additionally timestamps will be in
absolute system time, not starting from zero at the beginning of a
stream. The data type name for timestamps is stamp_t, defined as a
signed 64-bit integer. Output devices should not send a buffer out
until the time in the timestamp field has arrived. I would like to
follow SGI's lead, and adopt a multimedia timestamping system like
their UST (Unadjusted System Time). See
http://reality.sgi.com/cpirazzi_engr/lg/time/intro.html. [This link is
no longer valid.] UST uses timestamps that are 64-bit signed integers
(not struct timeval's) and given in nanosecond units. The UST clock
starts at zero when the system is booted and runs continuously and
uniformly. It takes a little over 292 years for UST to overflow. There
is no way to set the UST clock. The regular Linux time-of-day clock
can be changed periodically, which would cause errors if it were being
used for timestamping a multimedia stream. A real UST style clock will
require some support in the kernel that is not there yet. But in
anticipation, I will change the timestamp field to a 64-bit integer,
and I will change the v4l2_masterclock_gettime() function (used only
by drivers) to return a 64-bit integer.</para>
	</listitem>

	<listitem>
	  <para>A <structfield>sequence</structfield> field was added
to &v4l2-buffer;. The <structfield>sequence</structfield> field counts
captured frames, it is ignored by output devices. When a capture
driver drops a frame, the sequence number of that frame is
skipped.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 Version 0.20 incremental changes</title>
      <!-- Version number didn't change anymore, reason unknown. -->

      <para>1999-12-23: In &v4l2-vbi-format; the
<structfield>reserved1</structfield> field became
<structfield>offset</structfield>. Previously drivers were required to
clear the <structfield>reserved1</structfield> field.</para>

      <para>2000-01-13: The
      <constant>V4L2_FMT_FLAG_NOT_INTERLACED</constant> flag was added.</para>

      <para>2000-07-31: The <filename>linux/poll.h</filename> header
is now included by <filename>videodev.h</filename> for compatibility
with the original <filename>videodev.h</filename> file.</para>

      <para>2000-11-20: <constant>V4L2_TYPE_VBI_OUTPUT</constant> and
<constant>V4L2_PIX_FMT_Y41P</constant> were added.</para>

      <para>2000-11-25: <constant>V4L2_TYPE_VBI_INPUT</constant> was
added.</para>

      <para>2000-12-04: A couple typos in symbol names were fixed.</para>

      <para>2001-01-18: To avoid namespace conflicts the
<constant>fourcc</constant> macro defined in the
<filename>videodev.h</filename> header file was renamed to
<constant>v4l2_fourcc</constant>.</para>

      <para>2001-01-25: A possible driver-level compatibility problem
between the <filename>videodev.h</filename> file in Linux 2.4.0 and
the <filename>videodev.h</filename> file included in the
<filename>videodevX</filename> patch was fixed. Users of an earlier
version of <filename>videodevX</filename> on Linux 2.4.0 should
recompile their V4L and V4L2 drivers.</para>

      <para>2001-01-26: A possible kernel-level incompatibility
between the <filename>videodev.h</filename> file in the
<filename>videodevX</filename> patch and the
<filename>videodev.h</filename> file in Linux 2.2.x with devfs patches
applied was fixed.</para>

      <para>2001-03-02: Certain V4L ioctls which pass data in both
direction although they are defined with read-only parameter, did not
work correctly through the backward compatibility layer.
[Solution?]</para>

      <para>2001-04-13: Big endian 16-bit RGB formats were added.</para>

      <para>2001-09-17: New YUV formats and the &VIDIOC-G-FREQUENCY; and
&VIDIOC-S-FREQUENCY; ioctls were added. (The old
<constant>VIDIOC_G_FREQ</constant> and
<constant>VIDIOC_S_FREQ</constant> ioctls did not take multiple tuners
into account.)</para>

      <para>2000-09-18: <constant>V4L2_BUF_TYPE_VBI</constant> was
added. This may <emphasis>break compatibility</emphasis> as the
&VIDIOC-G-FMT; and &VIDIOC-S-FMT; ioctls may fail now if the struct
<structname>v4l2_fmt</structname> <structfield>type</structfield>
field does not contain <constant>V4L2_BUF_TYPE_VBI</constant>. In the
documentation of the &v4l2-vbi-format;
<structfield>offset</structfield> field the ambiguous phrase "rising
edge" was changed to "leading edge".</para>
    </section>

    <section>
      <title>V4L2 Version 0.20 2000-11-23</title>

      <para>A number of changes were made to the raw VBI
interface.</para>

      <orderedlist>
	<listitem>
	  <para>Figures clarifying the line numbering scheme were
added to the V4L2 API specification. The
<structfield>start</structfield>[0] and
<structfield>start</structfield>[1] fields no longer count line
numbers beginning at zero. Rationale: a) The previous definition was
unclear. b) The <structfield>start</structfield>[] values are ordinal
numbers. c) There is no point in inventing a new line numbering
scheme. We now use line number as defined by ITU-R, period.
Compatibility: Add one to the start values. Applications depending on
the previous semantics may not function correctly.</para>
	</listitem>

	<listitem>
	  <para>The restriction "count[0] &gt; 0 and count[1] &gt; 0"
has been relaxed  to "(count[0] + count[1]) &gt; 0". Rationale:
Drivers may allocate resources at scan line granularity and some data
services are transmitted only on the first field. The comment that
both <structfield>count</structfield> values will usually be equal is
misleading and pointless and has been removed. This change
<emphasis>breaks compatibility</emphasis> with earlier versions:
Drivers may return EINVAL, applications may not function
correctly.</para>
	</listitem>

	<listitem>
	  <para>Drivers are again permitted to return negative
(unknown) start values as proposed earlier. Why this feature was
dropped is unclear. This change may <emphasis>break
compatibility</emphasis> with applications depending on the start
values being positive. The use of <constant>EBUSY</constant> and
<constant>EINVAL</constant> error codes with the &VIDIOC-S-FMT; ioctl
was clarified. The &EBUSY; was finally documented, and the
<structfield>reserved2</structfield> field which was previously
mentioned only in the <filename>videodev.h</filename> header
file.</para>
	</listitem>

	<listitem>
	  <para>New buffer types
<constant>V4L2_TYPE_VBI_INPUT</constant> and
<constant>V4L2_TYPE_VBI_OUTPUT</constant> were added. The former is an
alias for the old <constant>V4L2_TYPE_VBI</constant>, the latter was
missing in the <filename>videodev.h</filename> file.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 Version 0.20 2002-07-25</title>
      <para>Added sliced VBI interface proposal.</para>
    </section>

    <section>
      <title>V4L2 in Linux 2.5.46, 2002-10</title>

      <para>Around October-November 2002, prior to an announced
feature freeze of Linux 2.5, the API was revised, drawing from
experience with V4L2 0.20. This unnamed version was finally merged
into Linux 2.5.46.</para>

      <orderedlist>
	<listitem>
	  <para>As specified in <xref linkend="related" />, drivers
must make related device functions available under all minor device
numbers.</para>
	</listitem>

	<listitem>
	  <para>The &func-open; function requires access mode
<constant>O_RDWR</constant> regardless of the device type. All V4L2
drivers exchanging data with applications must support the
<constant>O_NONBLOCK</constant> flag. The <constant>O_NOIO</constant>
flag, a V4L2 symbol which aliased the meaningless
<constant>O_TRUNC</constant> to indicate accesses without data
exchange (panel applications) was dropped. Drivers must stay in "panel
mode" until the application attempts to initiate a data exchange, see
<xref linkend="open" />.</para>
	</listitem>

	<listitem>
	  <para>The &v4l2-capability; changed dramatically. Note that
also the size of the structure changed, which is encoded in the ioctl
request code, thus older V4L2 devices will respond with an &EINVAL; to
the new &VIDIOC-QUERYCAP; ioctl.</para>

	  <para>There are new fields to identify the driver, a new RDS
device function <constant>V4L2_CAP_RDS_CAPTURE</constant>, the
<constant>V4L2_CAP_AUDIO</constant> flag indicates if the device has
any audio connectors, another I/O capability
<constant>V4L2_CAP_ASYNCIO</constant> can be flagged. In response to
these changes the <structfield>type</structfield> field became a bit
set and was merged into the <structfield>flags</structfield> field.
<constant>V4L2_FLAG_TUNER</constant> was renamed to
<constant>V4L2_CAP_TUNER</constant>,
<constant>V4L2_CAP_VIDEO_OVERLAY</constant> replaced
<constant>V4L2_FLAG_PREVIEW</constant> and
<constant>V4L2_CAP_VBI_CAPTURE</constant> and
<constant>V4L2_CAP_VBI_OUTPUT</constant> replaced
<constant>V4L2_FLAG_DATA_SERVICE</constant>.
<constant>V4L2_FLAG_READ</constant> and
<constant>V4L2_FLAG_WRITE</constant> were merged into
<constant>V4L2_CAP_READWRITE</constant>.</para>

	  <para>The redundant fields
<structfield>inputs</structfield>, <structfield>outputs</structfield>
and <structfield>audios</structfield> were removed. These properties
can be determined as described in <xref linkend="video" /> and <xref
linkend="audio" />.</para>

	  <para>The somewhat volatile and therefore barely useful
fields <structfield>maxwidth</structfield>,
<structfield>maxheight</structfield>,
<structfield>minwidth</structfield>,
<structfield>minheight</structfield>,
<structfield>maxframerate</structfield> were removed. This information
is available as described in <xref linkend="format" /> and
<xref linkend="standard" />.</para>

	  <para><constant>V4L2_FLAG_SELECT</constant> was removed. We
believe the select() function is important enough to require support
of it in all V4L2 drivers exchanging data with applications. The
redundant <constant>V4L2_FLAG_MONOCHROME</constant> flag was removed,
this information is available as described in <xref
	      linkend="format" />.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-input; the
<structfield>assoc_audio</structfield> field and the
<structfield>capability</structfield> field and its only flag
<constant>V4L2_INPUT_CAP_AUDIO</constant> was replaced by the new
<structfield>audioset</structfield> field. Instead of linking one
video input to one audio input this field reports all audio inputs
this video input combines with.</para>

	  <para>New fields are <structfield>tuner</structfield>
(reversing the former link from tuners to video inputs),
<structfield>std</structfield> and
<structfield>status</structfield>.</para>

	  <para>Accordingly &v4l2-output; lost its
<structfield>capability</structfield> and
<structfield>assoc_audio</structfield> fields.
<structfield>audioset</structfield>,
<structfield>modulator</structfield> and
<structfield>std</structfield> where added instead.</para>
	</listitem>

	<listitem>
	  <para>The &v4l2-audio; field
<structfield>audio</structfield> was renamed to
<structfield>index</structfield>, for consistency with other
structures. A new capability flag
<constant>V4L2_AUDCAP_STEREO</constant> was added to indicated if the
audio input in question supports stereo sound.
<constant>V4L2_AUDCAP_EFFECTS</constant> and the corresponding
<constant>V4L2_AUDMODE</constant> flags where removed. This can be
easily implemented using controls. (However the same applies to AVL
which is still there.)</para>

	  <para>Again for consistency the &v4l2-audioout; field
<structfield>audio</structfield> was renamed to
<structfield>index</structfield>.</para>
	</listitem>

	<listitem>
	  <para>The &v4l2-tuner;
<structfield>input</structfield> field was replaced by an
<structfield>index</structfield> field, permitting devices with
multiple tuners. The link between video inputs and tuners is now
reversed, inputs point to their tuner. The
<structfield>std</structfield> substructure became a
simple set (more about this below) and moved into &v4l2-input;. A
<structfield>type</structfield> field was added.</para>

	  <para>Accordingly in &v4l2-modulator; the
<structfield>output</structfield> was replaced by an
<structfield>index</structfield> field.</para>

	  <para>In &v4l2-frequency; the
<structfield>port</structfield> field was replaced by a
<structfield>tuner</structfield> field containing the respective tuner
or modulator index number. A tuner <structfield>type</structfield>
field was added and the <structfield>reserved</structfield> field
became larger for future extensions (satellite tuners in
particular).</para>
	</listitem>

	<listitem>
	  <para>The idea of completely transparent video standards was
dropped. Experience showed that applications must be able to work with
video standards beyond presenting the user a menu. Instead of
enumerating supported standards with an ioctl applications can now
refer to standards by &v4l2-std-id; and symbols defined in the
<filename>videodev2.h</filename> header file. For details see <xref
	      linkend="standard" />. The &VIDIOC-G-STD; and
&VIDIOC-S-STD; now take a pointer to this type as argument.
&VIDIOC-QUERYSTD; was added to autodetect the received standard, if
the hardware has this capability. In &v4l2-standard; an
<structfield>index</structfield> field was added for &VIDIOC-ENUMSTD;.
A &v4l2-std-id; field named <structfield>id</structfield> was added as
machine readable identifier, also replacing the
<structfield>transmission</structfield> field. The misleading
<structfield>framerate</structfield> field was renamed
to <structfield>frameperiod</structfield>. The now obsolete
<structfield>colorstandard</structfield> information, originally
needed to distguish between variations of standards, were
removed.</para>

	  <para>Struct <structname>v4l2_enumstd</structname> ceased to
be. &VIDIOC-ENUMSTD; now takes a pointer to a &v4l2-standard;
directly. The information which standards are supported by a
particular video input or output moved into &v4l2-input; and
&v4l2-output; fields named <structfield>std</structfield>,
respectively.</para>
	</listitem>

	<listitem>
	  <para>The &v4l2-queryctrl; fields
<structfield>category</structfield> and
<structfield>group</structfield> did not catch on and/or were not
implemented as expected and therefore removed.</para>
	</listitem>

	<listitem>
	  <para>The &VIDIOC-TRY-FMT; ioctl was added to negotiate data
formats as with &VIDIOC-S-FMT;, but without the overhead of
programming the hardware and regardless of I/O in progress.</para>

	  <para>In &v4l2-format; the <structfield>fmt</structfield>
union was extended to contain &v4l2-window;. All image format
negotiations are now possible with <constant>VIDIOC_G_FMT</constant>,
<constant>VIDIOC_S_FMT</constant> and
<constant>VIDIOC_TRY_FMT</constant>; ioctl. The
<constant>VIDIOC_G_WIN</constant> and
<constant>VIDIOC_S_WIN</constant> ioctls to prepare for a video
overlay were removed. The <structfield>type</structfield> field
changed to type &v4l2-buf-type; and the buffer type names changed as
follows.<informaltable>
	      <tgroup cols="2">
		<thead>
		  <row>
		    <entry>Old defines</entry>
		    <entry>&v4l2-buf-type;</entry>
		  </row>
		</thead>
		<tbody valign="top">
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_CAPTURE</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant></entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_CODECIN</constant></entry>
		    <entry>Omitted for now</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_CODECOUT</constant></entry>
		    <entry>Omitted for now</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_EFFECTSIN</constant></entry>
		    <entry>Omitted for now</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_EFFECTSIN2</constant></entry>
		    <entry>Omitted for now</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_EFFECTSOUT</constant></entry>
		    <entry>Omitted for now</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_VIDEOOUT</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_VBI_CAPTURE</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_VBI_OUTPUT</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</constant></entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_BUF_TYPE_PRIVATE_BASE</constant></entry>
		    <entry><constant>V4L2_BUF_TYPE_PRIVATE</constant></entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable></para>
	</listitem>

	<listitem>
	  <para>In &v4l2-fmtdesc; a &v4l2-buf-type; field named
<structfield>type</structfield> was added as in &v4l2-format;. The
<constant>VIDIOC_ENUM_FBUFFMT</constant> ioctl is no longer needed and
was removed. These calls can be replaced by &VIDIOC-ENUM-FMT; with
type <constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-pix-format; the
<structfield>depth</structfield> field was removed, assuming
applications which recognize the format by its four-character-code
already know the color depth, and others do not care about it. The
same rationale lead to the removal of the
<constant>V4L2_FMT_FLAG_COMPRESSED</constant> flag. The
<constant>V4L2_FMT_FLAG_SWCONVECOMPRESSED</constant> flag was removed
because drivers are not supposed to convert images in kernel space. A
user library of conversion functions should be provided instead. The
<constant>V4L2_FMT_FLAG_BYTESPERLINE</constant> flag was redundant.
Applications can set the <structfield>bytesperline</structfield> field
to zero to get a reasonable default. Since the remaining flags were
replaced as well, the <structfield>flags</structfield> field itself
was removed.</para>
	  <para>The interlace flags were replaced by a &v4l2-field;
value in a newly added <structfield>field</structfield>
field.<informaltable>
	      <tgroup cols="2">
		<thead>
		  <row>
		    <entry>Old flag</entry>
		    <entry>&v4l2-field;</entry>
		  </row>
		</thead>
		<tbody valign="top">
		  <row>
		    <entry><constant>V4L2_FMT_FLAG_NOT_INTERLACED</constant></entry>
		    <entry>?</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FMT_FLAG_INTERLACED</constant>
= <constant>V4L2_FMT_FLAG_COMBINED</constant></entry>
		    <entry><constant>V4L2_FIELD_INTERLACED</constant></entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FMT_FLAG_TOPFIELD</constant>
= <constant>V4L2_FMT_FLAG_ODDFIELD</constant></entry>
		    <entry><constant>V4L2_FIELD_TOP</constant></entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FMT_FLAG_BOTFIELD</constant>
= <constant>V4L2_FMT_FLAG_EVENFIELD</constant></entry>
		    <entry><constant>V4L2_FIELD_BOTTOM</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_FIELD_SEQ_TB</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_FIELD_SEQ_BT</constant></entry>
		  </row>
		  <row>
		    <entry><constant>-</constant></entry>
		    <entry><constant>V4L2_FIELD_ALTERNATE</constant></entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable></para>

	  <para>The color space flags were replaced by a
&v4l2-colorspace; value in a newly added
<structfield>colorspace</structfield> field, where one of
<constant>V4L2_COLORSPACE_SMPTE170M</constant>,
<constant>V4L2_COLORSPACE_BT878</constant>,
<constant>V4L2_COLORSPACE_470_SYSTEM_M</constant> or
<constant>V4L2_COLORSPACE_470_SYSTEM_BG</constant> replaces
<constant>V4L2_FMT_CS_601YUV</constant>.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-requestbuffers; the
<structfield>type</structfield> field was properly defined as
&v4l2-buf-type;. Buffer types changed as mentioned above. A new
<structfield>memory</structfield> field of type &v4l2-memory; was
added to distinguish between I/O methods using buffers allocated
by the driver or the application. See <xref linkend="io" /> for
details.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-buffer; the <structfield>type</structfield>
field was properly defined as &v4l2-buf-type;. Buffer types changed as
mentioned above. A <structfield>field</structfield> field of type
&v4l2-field; was added to indicate if a buffer contains a top or
bottom field. The old field flags were removed. Since no unadjusted
system time clock was added to the kernel as planned, the
<structfield>timestamp</structfield> field changed back from type
stamp_t, an unsigned 64 bit integer expressing the sample time in
nanoseconds, to struct <structname>timeval</structname>. With the
addition of a second memory mapping method the
<structfield>offset</structfield> field moved into union
<structfield>m</structfield>, and a new
<structfield>memory</structfield> field of type &v4l2-memory; was
added to distinguish between I/O methods. See <xref linkend="io" />
for details.</para>

	  <para>The <constant>V4L2_BUF_REQ_CONTIG</constant>
flag was used by the V4L compatibility layer, after changes to this
code it was no longer needed. The
<constant>V4L2_BUF_ATTR_DEVICEMEM</constant> flag would indicate if
the buffer was indeed allocated in device memory rather than DMA-able
system memory. It was barely useful and so was removed.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-framebuffer; the
<structfield>base[3]</structfield> array anticipating double- and
triple-buffering in off-screen video memory, however without defining
a synchronization mechanism, was replaced by a single pointer. The
<constant>V4L2_FBUF_CAP_SCALEUP</constant> and
<constant>V4L2_FBUF_CAP_SCALEDOWN</constant> flags were removed.
Applications can determine this capability more accurately using the
new cropping and scaling interface. The
<constant>V4L2_FBUF_CAP_CLIPPING</constant> flag was replaced by
<constant>V4L2_FBUF_CAP_LIST_CLIPPING</constant> and
<constant>V4L2_FBUF_CAP_BITMAP_CLIPPING</constant>.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-clip; the <structfield>x</structfield>,
<structfield>y</structfield>, <structfield>width</structfield> and
<structfield>height</structfield> field moved into a
<structfield>c</structfield> substructure of type &v4l2-rect;. The
<structfield>x</structfield> and <structfield>y</structfield> fields
were renamed to <structfield>left</structfield> and
<structfield>top</structfield>, &ie; offsets to a context dependent
origin.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-window; the <structfield>x</structfield>,
<structfield>y</structfield>, <structfield>width</structfield> and
<structfield>height</structfield> field moved into a
<structfield>w</structfield> substructure as above. A
<structfield>field</structfield> field of type %v4l2-field; was added
to distinguish between field and frame (interlaced) overlay.</para>
	</listitem>

	<listitem>
	  <para>The digital zoom interface, including struct
<structname>v4l2_zoomcap</structname>, struct
<structname>v4l2_zoom</structname>,
<constant>V4L2_ZOOM_NONCAP</constant> and
<constant>V4L2_ZOOM_WHILESTREAMING</constant> was replaced by a new
cropping and scaling interface. The previously unused struct
<structname>v4l2_cropcap</structname> and
<structname>v4l2_crop</structname> where redefined for this purpose.
See <xref linkend="crop" /> for details.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-vbi-format; the
<structfield>SAMPLE_FORMAT</structfield> field now contains a
four-character-code as used to identify video image formats and
<constant>V4L2_PIX_FMT_GREY</constant> replaces the
<constant>V4L2_VBI_SF_UBYTE</constant> define. The
<structfield>reserved</structfield> field was extended.</para>
	</listitem>

	<listitem>
	  <para>In &v4l2-captureparm; the type of the
<structfield>timeperframe</structfield> field changed from unsigned
long to &v4l2-fract;. This allows the accurate expression of multiples
of the NTSC-M frame rate 30000 / 1001. A new field
<structfield>readbuffers</structfield> was added to control the driver
behaviour in read I/O mode.</para>

	  <para>Similar changes were made to &v4l2-outputparm;.</para>
	</listitem>

	<listitem>
	  <para>The struct <structname>v4l2_performance</structname>
and <constant>VIDIOC_G_PERF</constant> ioctl were dropped. Except when
using the <link linkend="rw">read/write I/O method</link>, which is
limited anyway, this information is already available to
applications.</para>
	</listitem>

	<listitem>
	  <para>The example transformation from RGB to YCbCr color
space in the old V4L2 documentation was inaccurate, this has been
corrected in <xref linkend="pixfmt" />.<!-- 0.5670G should be
0.587, and 127/112 != 255/224 --></para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 2003-06-19</title>

      <orderedlist>
	<listitem>
	  <para>A new capability flag
<constant>V4L2_CAP_RADIO</constant> was added for radio devices. Prior
to this change radio devices would identify solely by having exactly one
tuner whose type field reads <constant>V4L2_TUNER_RADIO</constant>.</para>
	</listitem>

	<listitem>
	  <para>An optional driver access priority mechanism was
added, see <xref linkend="app-pri" /> for details.</para>
	</listitem>

	<listitem>
	  <para>The audio input and output interface was found to be
incomplete.</para>
	  <para>Previously the &VIDIOC-G-AUDIO;
ioctl would enumerate the available audio inputs. An ioctl to
determine the current audio input, if more than one combines with the
current video input, did not exist. So
<constant>VIDIOC_G_AUDIO</constant> was renamed to
<constant>VIDIOC_G_AUDIO_OLD</constant>, this ioctl will be removed in
the future. The &VIDIOC-ENUMAUDIO; ioctl was added to enumerate
audio inputs, while &VIDIOC-G-AUDIO; now reports the current audio
input.</para>
	  <para>The same changes were made to &VIDIOC-G-AUDOUT; and
&VIDIOC-ENUMAUDOUT;.</para>
	  <para>Until further the "videodev" module will automatically
translate between the old and new ioctls, but drivers and applications
must be updated to successfully compile again.</para>
	</listitem>

	<listitem>
	  <para>The &VIDIOC-OVERLAY; ioctl was incorrectly defined with
write-read parameter. It was changed to write-only, while the write-read
version was renamed to <constant>VIDIOC_OVERLAY_OLD</constant>. The old
ioctl will be removed in the future. Until further the "videodev"
kernel module will automatically translate to the new version, so drivers
must be recompiled, but not applications.</para>
	</listitem>

	<listitem>
	  <para><xref linkend="overlay" /> incorrectly stated that
clipping rectangles define regions where the video can be seen.
Correct is that clipping rectangles define regions where
<emphasis>no</emphasis> video shall be displayed and so the graphics
surface can be seen.</para>
	</listitem>

	<listitem>
	  <para>The &VIDIOC-S-PARM; and &VIDIOC-S-CTRL; ioctls were
defined with write-only parameter, inconsistent with other ioctls
modifying their argument. They were changed to write-read, while a
<constant>_OLD</constant> suffix was added to the write-only versions.
The old ioctls will be removed in the future. Drivers and
applications assuming a constant parameter need an update.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 2003-11-05</title>
      <orderedlist>
	<listitem>
	  <para>In <xref linkend="pixfmt-rgb" /> the following pixel
formats were incorrectly transferred from Bill Dirks' V4L2
specification. Descriptions below refer to bytes in memory, in
ascending address order.<informaltable>
	      <tgroup cols="3">
		<thead>
		  <row>
		    <entry>Symbol</entry>
		    <entry>In this document prior to revision
0.5</entry>
		    <entry>Corrected</entry>
		  </row>
		</thead>
		<tbody valign="top">
		  <row>
		    <entry><constant>V4L2_PIX_FMT_RGB24</constant></entry>
		    <entry>B, G, R</entry>
		    <entry>R, G, B</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_PIX_FMT_BGR24</constant></entry>
		    <entry>R, G, B</entry>
		    <entry>B, G, R</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_PIX_FMT_RGB32</constant></entry>
		    <entry>B, G, R, X</entry>
		    <entry>R, G, B, X</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_PIX_FMT_BGR32</constant></entry>
		    <entry>R, G, B, X</entry>
		    <entry>B, G, R, X</entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable> The
<constant>V4L2_PIX_FMT_BGR24</constant> example was always
correct.</para>
	  <para>In <xref linkend="v4l-image-properties" /> the mapping
of the V4L <constant>VIDEO_PALETTE_RGB24</constant> and
<constant>VIDEO_PALETTE_RGB32</constant> formats to V4L2 pixel formats
was accordingly corrected.</para>
	</listitem>

	<listitem>
	  <para>Unrelated to the fixes above, drivers may still
interpret some V4L2 RGB pixel formats differently. These issues have
yet to be addressed, for details see <xref
	      linkend="pixfmt-rgb" />.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.6, 2004-05-09</title>
      <orderedlist>
	<listitem>
	  <para>The &VIDIOC-CROPCAP; ioctl was incorrectly defined
with read-only parameter. It is now defined as write-read ioctl, while
the read-only version was renamed to
<constant>VIDIOC_CROPCAP_OLD</constant>. The old ioctl will be removed
in the future.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.8</title>
      <orderedlist>
	<listitem>
	  <para>A new field <structfield>input</structfield> (former
<structfield>reserved[0]</structfield>) was added to the &v4l2-buffer;
structure. Purpose of this field is to alternate between video inputs
(&eg; cameras) in step with the video capturing process. This function
must be enabled with the new <constant>V4L2_BUF_FLAG_INPUT</constant>
flag. The <structfield>flags</structfield> field is no longer
read-only.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2004-08-01</title>

      <orderedlist>
	<listitem>
	  <para>The return value of the
<xref linkend="func-open" /> function was incorrectly documented.</para>
	</listitem>

	<listitem>
	  <para>Audio output ioctls end in -AUDOUT, not -AUDIOOUT.</para>
	</listitem>

	<listitem>
	  <para>In the Current Audio Input example the
<constant>VIDIOC_G_AUDIO</constant> ioctl took the wrong
argument.</para>
	</listitem>

	<listitem>
	  <para>The documentation of the &VIDIOC-QBUF; and
&VIDIOC-DQBUF; ioctls did not mention the &v4l2-buffer;
<structfield>memory</structfield> field. It was also missing from
examples. Also on the <constant>VIDIOC_DQBUF</constant> page the &EIO;
was not documented.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.14</title>
      <orderedlist>
	<listitem>
	  <para>A new sliced VBI interface was added. It is documented
in <xref linkend="sliced" /> and replaces the interface first
proposed in V4L2 specification 0.8.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.15</title>
      <orderedlist>
	<listitem>
	  <para>The &VIDIOC-LOG-STATUS; ioctl was added.</para>
	</listitem>

	<listitem>
	  <para>New video standards
<constant>V4L2_STD_NTSC_443</constant>,
<constant>V4L2_STD_SECAM_LC</constant>,
<constant>V4L2_STD_SECAM_DK</constant> (a set of SECAM D, K and K1),
and <constant>V4L2_STD_ATSC</constant> (a set of
<constant>V4L2_STD_ATSC_8_VSB</constant> and
<constant>V4L2_STD_ATSC_16_VSB</constant>) were defined. Note the
<constant>V4L2_STD_525_60</constant> set now includes
<constant>V4L2_STD_NTSC_443</constant>. See also <xref
	      linkend="v4l2-std-id" />.</para>
	</listitem>

	<listitem>
	  <para>The <constant>VIDIOC_G_COMP</constant> and
<constant>VIDIOC_S_COMP</constant> ioctl were renamed to
<constant>VIDIOC_G_MPEGCOMP</constant> and
<constant>VIDIOC_S_MPEGCOMP</constant> respectively. Their argument
was replaced by a struct
<structname>v4l2_mpeg_compression</structname> pointer. (The
<constant>VIDIOC_G_MPEGCOMP</constant> and
<constant>VIDIOC_S_MPEGCOMP</constant> ioctls where removed in Linux
2.6.25.)</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2005-11-27</title>
      <para>The capture example in <xref linkend="capture-example" />
called the &VIDIOC-S-CROP; ioctl without checking if cropping is
supported. In the video standard selection example in
<xref linkend="standard" /> the &VIDIOC-S-STD; call used the wrong
argument type.</para>
    </section>

    <section>
      <title>V4L2 spec erratum 2006-01-10</title>
      <orderedlist>
	<listitem>
	  <para>The <constant>V4L2_IN_ST_COLOR_KILL</constant> flag in
&v4l2-input; not only indicates if the color killer is enabled, but
also if it is active. (The color killer disables color decoding when
it detects no color in the video signal to improve the image
quality.)</para>
	</listitem>

	<listitem>
	  <para>&VIDIOC-S-PARM; is a write-read ioctl, not write-only as
stated on its reference page. The ioctl changed in 2003 as noted above.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2006-02-03</title>
      <orderedlist>
	<listitem>
	  <para>In &v4l2-captureparm; and &v4l2-outputparm; the
<structfield>timeperframe</structfield> field gives the time in
seconds, not microseconds.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2006-02-04</title>
      <orderedlist>
	<listitem>
	  <para>The <structfield>clips</structfield> field in
&v4l2-window; must point to an array of &v4l2-clip;, not a linked
list, because drivers ignore the struct
<structname>v4l2_clip</structname>.<structfield>next</structfield>
pointer.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.17</title>
      <orderedlist>
	<listitem>
	  <para>New video standard macros were added:
<constant>V4L2_STD_NTSC_M_KR</constant> (NTSC M South Korea), and the
sets <constant>V4L2_STD_MN</constant>,
<constant>V4L2_STD_B</constant>, <constant>V4L2_STD_GH</constant> and
<constant>V4L2_STD_DK</constant>. The
<constant>V4L2_STD_NTSC</constant> and
<constant>V4L2_STD_SECAM</constant> sets now include
<constant>V4L2_STD_NTSC_M_KR</constant> and
<constant>V4L2_STD_SECAM_LC</constant> respectively.</para>
	</listitem>

	<listitem>
	  <para>A new <constant>V4L2_TUNER_MODE_LANG1_LANG2</constant>
was defined to record both languages of a bilingual program. The
use of <constant>V4L2_TUNER_MODE_STEREO</constant> for this purpose
is deprecated now. See the &VIDIOC-G-TUNER; section for
details.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2006-09-23 (Draft 0.15)</title>
      <orderedlist>
	<listitem>
	  <para>In various places
<constant>V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</constant> and
<constant>V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</constant> of the sliced VBI
interface were not mentioned along with other buffer types.</para>
	</listitem>

	<listitem>
	  <para>In <xref linkend="vidioc-g-audio" /> it was clarified
that the &v4l2-audio; <structfield>mode</structfield> field is a flags
field.</para>
	</listitem>

	<listitem>
	  <para><xref linkend="vidioc-querycap" /> did not mention the
sliced VBI and radio capability flags.</para>
	</listitem>

	<listitem>
	  <para>In <xref linkend="vidioc-g-frequency" /> it was
clarified that applications must initialize the tuner
<structfield>type</structfield> field of &v4l2-frequency; before
calling &VIDIOC-S-FREQUENCY;.</para>
	</listitem>

	<listitem>
	  <para>The <structfield>reserved</structfield> array
in &v4l2-requestbuffers; has 2 elements, not 32.</para>
	</listitem>

	<listitem>
	  <para>In <xref linkend="output" /> and <xref
	      linkend="raw-vbi" /> the device file names
<filename>/dev/vout</filename> which never caught on were replaced
by <filename>/dev/video</filename>.</para>
	</listitem>

	<listitem>
	  <para>With Linux 2.6.15 the possible range for VBI device minor
numbers was extended from 224-239 to 224-255. Accordingly device file names
<filename>/dev/vbi0</filename> to <filename>/dev/vbi31</filename> are
possible now.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.18</title>
      <orderedlist>
	<listitem>
	  <para>New ioctls &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS;
and &VIDIOC-TRY-EXT-CTRLS; were added, a flag to skip unsupported
controls with &VIDIOC-QUERYCTRL;, new control types
<constant>V4L2_CTRL_TYPE_INTEGER64</constant> and
<constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant> (<xref
	      linkend="v4l2-ctrl-type" />), and new control flags
<constant>V4L2_CTRL_FLAG_READ_ONLY</constant>,
<constant>V4L2_CTRL_FLAG_UPDATE</constant>,
<constant>V4L2_CTRL_FLAG_INACTIVE</constant> and
<constant>V4L2_CTRL_FLAG_SLIDER</constant> (<xref
	      linkend="control-flags" />). See <xref
	      linkend="extended-controls" /> for details.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.19</title>
      <orderedlist>
	<listitem>
	  <para>In &v4l2-sliced-vbi-cap; a buffer type field was added
replacing a reserved field. Note on architectures where the size of
enum types differs from int types the size of the structure changed.
The &VIDIOC-G-SLICED-VBI-CAP; ioctl was redefined from being read-only
to write-read. Applications must initialize the type field and clear
the reserved fields now. These changes may <emphasis>break the
compatibility</emphasis> with older drivers and applications.</para>
	</listitem>

	<listitem>
	  <para>The ioctls &VIDIOC-ENUM-FRAMESIZES; and
&VIDIOC-ENUM-FRAMEINTERVALS; were added.</para>
	</listitem>

	<listitem>
	  <para>A new pixel format <constant>V4L2_PIX_FMT_RGB444</constant> (<xref
linkend="rgb-formats" />) was added.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 spec erratum 2006-10-12 (Draft 0.17)</title>
      <orderedlist>
	<listitem>
	  <para><constant>V4L2_PIX_FMT_HM12</constant> (<xref
linkend="reserved-formats" />) is a YUV 4:2:0, not 4:2:2 format.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.21</title>
      <orderedlist>
	<listitem>
	  <para>The <filename>videodev2.h</filename> header file is
now dual licensed under GNU General Public License version two or
later, and under a 3-clause BSD-style license.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.22</title>
      <orderedlist>
	<listitem>
	  <para>Two new field orders
	  <constant>V4L2_FIELD_INTERLACED_TB</constant> and
	  <constant>V4L2_FIELD_INTERLACED_BT</constant> were
	  added. See <xref linkend="v4l2-field" /> for details.</para>
	</listitem>

	<listitem>
	  <para>Three new clipping/blending methods with a global or
straight or inverted local alpha value were added to the video overlay
interface. See the description of the &VIDIOC-G-FBUF; and
&VIDIOC-S-FBUF; ioctls for details.</para>
	  <para>A new <structfield>global_alpha</structfield> field
was added to <link
linkend="v4l2-window"><structname>v4l2_window</structname></link>,
extending the structure. This may <emphasis>break
compatibility</emphasis> with applications using a struct
<structname>v4l2_window</structname> directly. However the <link
linkend="vidioc-g-fmt">VIDIOC_G/S/TRY_FMT</link> ioctls, which take a
pointer to a <link linkend="v4l2-format">v4l2_format</link> parent
structure with padding bytes at the end, are not affected.</para>
	</listitem>

	<listitem>
	  <para>The format of the <structfield>chromakey</structfield>
field in &v4l2-window; changed from "host order RGB32" to a pixel
value in the same format as the framebuffer. This may <emphasis>break
compatibility</emphasis> with existing applications. Drivers
supporting the "host order RGB32" format are not known.</para>
	</listitem>

      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.24</title>
      <orderedlist>
	<listitem>
	  <para>The pixel formats
<constant>V4L2_PIX_FMT_PAL8</constant>,
<constant>V4L2_PIX_FMT_YUV444</constant>,
<constant>V4L2_PIX_FMT_YUV555</constant>,
<constant>V4L2_PIX_FMT_YUV565</constant> and
<constant>V4L2_PIX_FMT_YUV32</constant> were added.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.25</title>
      <orderedlist>
	<listitem>
	  <para>The pixel formats <link linkend="V4L2-PIX-FMT-Y16">
<constant>V4L2_PIX_FMT_Y16</constant></link> and <link
linkend="V4L2-PIX-FMT-SBGGR16">
<constant>V4L2_PIX_FMT_SBGGR16</constant></link> were added.</para>
	</listitem>
	<listitem>
	  <para>New <link linkend="control">controls</link>
<constant>V4L2_CID_POWER_LINE_FREQUENCY</constant>,
<constant>V4L2_CID_HUE_AUTO</constant>,
<constant>V4L2_CID_WHITE_BALANCE_TEMPERATURE</constant>,
<constant>V4L2_CID_SHARPNESS</constant> and
<constant>V4L2_CID_BACKLIGHT_COMPENSATION</constant> were added. The
controls <constant>V4L2_CID_BLACK_LEVEL</constant>,
<constant>V4L2_CID_WHITENESS</constant>,
<constant>V4L2_CID_HCENTER</constant> and
<constant>V4L2_CID_VCENTER</constant> were deprecated.
</para>
	</listitem>
	<listitem>
	  <para>A <link linkend="camera-controls">Camera controls
class</link> was added, with the new controls
<constant>V4L2_CID_EXPOSURE_AUTO</constant>,
<constant>V4L2_CID_EXPOSURE_ABSOLUTE</constant>,
<constant>V4L2_CID_EXPOSURE_AUTO_PRIORITY</constant>,
<constant>V4L2_CID_PAN_RELATIVE</constant>,
<constant>V4L2_CID_TILT_RELATIVE</constant>,
<constant>V4L2_CID_PAN_RESET</constant>,
<constant>V4L2_CID_TILT_RESET</constant>,
<constant>V4L2_CID_PAN_ABSOLUTE</constant>,
<constant>V4L2_CID_TILT_ABSOLUTE</constant>,
<constant>V4L2_CID_FOCUS_ABSOLUTE</constant>,
<constant>V4L2_CID_FOCUS_RELATIVE</constant> and
<constant>V4L2_CID_FOCUS_AUTO</constant>.</para>
	</listitem>
	<listitem>
	  <para>The <constant>VIDIOC_G_MPEGCOMP</constant> and
<constant>VIDIOC_S_MPEGCOMP</constant> ioctls, which were superseded
by the <link linkend="extended-controls">extended controls</link>
interface in Linux 2.6.18, where finally removed from the
<filename>videodev2.h</filename> header file.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.26</title>
      <orderedlist>
	<listitem>
	  <para>The pixel formats
<constant>V4L2_PIX_FMT_Y16</constant> and
<constant>V4L2_PIX_FMT_SBGGR16</constant> were added.</para>
	</listitem>
	<listitem>
	  <para>Added user controls
<constant>V4L2_CID_CHROMA_AGC</constant> and
<constant>V4L2_CID_COLOR_KILLER</constant>.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.27</title>
      <orderedlist>
	<listitem>
	  <para>The &VIDIOC-S-HW-FREQ-SEEK; ioctl and the
<constant>V4L2_CAP_HW_FREQ_SEEK</constant> capability were added.</para>
	</listitem>
	<listitem>
	  <para>The pixel formats
<constant>V4L2_PIX_FMT_YVYU</constant>,
<constant>V4L2_PIX_FMT_PCA501</constant>,
<constant>V4L2_PIX_FMT_PCA505</constant>,
<constant>V4L2_PIX_FMT_PCA508</constant>,
<constant>V4L2_PIX_FMT_PCA561</constant>,
<constant>V4L2_PIX_FMT_SGBRG8</constant>,
<constant>V4L2_PIX_FMT_PAC207</constant> and
<constant>V4L2_PIX_FMT_PJPG</constant> were added.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.28</title>
      <orderedlist>
	<listitem>
	  <para>Added <constant>V4L2_MPEG_AUDIO_ENCODING_AAC</constant> and
<constant>V4L2_MPEG_AUDIO_ENCODING_AC3</constant> MPEG audio encodings.</para>
	</listitem>
	<listitem>
	  <para>Added <constant>V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC</constant> MPEG
video encoding.</para>
	</listitem>
	<listitem>
	  <para>The pixel formats
<constant>V4L2_PIX_FMT_SGRBG10</constant> and
<constant>V4L2_PIX_FMT_SGRBG10DPCM8</constant> were added.</para>
	</listitem>
      </orderedlist>
    </section>

    <section>
      <title>V4L2 in Linux 2.6.29</title>
      <orderedlist>
	<listitem>
	  <para>The <constant>VIDIOC_G_CHIP_IDENT</constant> ioctl was renamed
to <constant>VIDIOC_G_CHIP_IDENT_OLD</constant> and &VIDIOC-DBG-G-CHIP-IDENT;
was introduced in its place. The old struct <structname>v4l2_chip_ident</structname>
was renamed to <structname id="v4l2-chip-ident-old">v4l2_chip_ident_old</structname>.</para>
	</listitem>
	<listitem>
	  <para>The pixel formats
<constant>V4L2_PIX_FMT_VYUY</constant>,
<constant>V4L2_PIX_FMT_NV16</constant> and
<constant>V4L2_PIX_FMT_NV61</constant> were added.</para>
	</listitem>
	<listitem>
	  <para>Added camera controls
<constant>V4L2_CID_ZOOM_ABSOLUTE</constant>,
<constant>V4L2_CID_ZOOM_RELATIVE</constant>,
<constant>V4L2_CID_ZOOM_CONTINUOUS</constant> and
<constant>V4L2_CID_PRIVACY</constant>.</para>
	</listitem>
      </orderedlist>
    </section>
    <section>
      <title>V4L2 in Linux 2.6.30</title>
      <orderedlist>
	<listitem>
	  <para>New control flag <constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant> was added.</para>
	</listitem>
	<listitem>
	  <para>New control <constant>V4L2_CID_COLORFX</constant> was added.</para>
	</listitem>
      </orderedlist>
    </section>
    <section>
      <title>V4L2 in Linux 2.6.32</title>
      <orderedlist>
	<listitem>
	  <para>In order to be easier to compare a V4L2 API and a kernel
version, now V4L2 API is numbered using the Linux Kernel version numeration.</para>
	</listitem>
	<listitem>
	  <para>Finalized the RDS capture API. See <xref linkend="rds" /> for
more information.</para>
	</listitem>
	<listitem>
	  <para>Added new capabilities for modulators and RDS encoders.</para>
	</listitem>
	<listitem>
	  <para>Add description for libv4l API.</para>
	</listitem>
	<listitem>
	  <para>Added support for string controls via new type <constant>V4L2_CTRL_TYPE_STRING</constant>.</para>
	</listitem>
	<listitem>
	  <para>Added <constant>V4L2_CID_BAND_STOP_FILTER</constant> documentation.</para>
	</listitem>
	<listitem>
	  <para>Added FM Modulator (FM TX) Extended Control Class: <constant>V4L2_CTRL_CLASS_FM_TX</constant> and their Control IDs.</para>
	</listitem>
	<listitem>
	  <para>Added Remote Controller chapter, describing the default Remote Controller mapping for media devices.</para>
	</listitem>
      </orderedlist>
    </section>
    <section>
      <title>V4L2 in Linux 2.6.33</title>
      <orderedlist>
	<listitem>
	  <para>Added support for Digital Video timings in order to support HDTV receivers and transmitters.</para>
	</listitem>
      </orderedlist>
    </section>
   </section>

   <section id="other">
     <title>Relation of V4L2 to other Linux multimedia APIs</title>

    <section id="xvideo">
      <title>X Video Extension</title>

      <para>The X Video Extension (abbreviated XVideo or just Xv) is
an extension of the X Window system, implemented for example by the
XFree86 project. Its scope is similar to V4L2, an API to video capture
and output devices for X clients. Xv allows applications to display
live video in a window, send window contents to a TV output, and
capture or output still images in XPixmaps<footnote>
	  <para>This is not implemented in XFree86.</para>
	</footnote>. With their implementation XFree86 makes the
extension available across many operating systems and
architectures.</para>

      <para>Because the driver is embedded into the X server Xv has a
number of advantages over the V4L2 <link linkend="overlay">video
overlay interface</link>. The driver can easily determine the overlay
target, &ie; visible graphics memory or off-screen buffers for a
destructive overlay. It can program the RAMDAC for a non-destructive
overlay, scaling or color-keying, or the clipping functions of the
video capture hardware, always in sync with drawing operations or
windows moving or changing their stacking order.</para>

      <para>To combine the advantages of Xv and V4L a special Xv
driver exists in XFree86 and XOrg, just programming any overlay capable
Video4Linux device it finds. To enable it
<filename>/etc/X11/XF86Config</filename> must contain these lines:</para>
      <para><screen>
Section "Module"
    Load "v4l"
EndSection</screen></para>

      <para>As of XFree86 4.2 this driver still supports only V4L
ioctls, however it should work just fine with all V4L2 devices through
the V4L2 backward-compatibility layer. Since V4L2 permits multiple
opens it is possible (if supported by the V4L2 driver) to capture
video while an X client requested video overlay. Restrictions of
simultaneous capturing and overlay are discussed in <xref
	  linkend="overlay" /> apply.</para>

      <para>Only marginally related to V4L2, XFree86 extended Xv to
support hardware YUV to RGB conversion and scaling for faster video
playback, and added an interface to MPEG-2 decoding hardware. This API
is useful to display images captured with V4L2 devices.</para>
    </section>

    <section>
      <title>Digital Video</title>

      <para>V4L2 does not support digital terrestrial, cable or
satellite broadcast. A separate project aiming at digital receivers
exists. You can find its homepage at <ulink
url="http://linuxtv.org">http://linuxtv.org</ulink>. The Linux DVB API
has no connection to the V4L2 API except that drivers for hybrid
hardware may support both.</para>
    </section>

    <section>
      <title>Audio Interfaces</title>

      <para>[to do - OSS/ALSA]</para>
    </section>
  </section>

  <section id="experimental">
    <title>Experimental API Elements</title>

    <para>The following V4L2 API elements are currently experimental
and may change in the future.</para>

    <itemizedlist>
      <listitem>
	<para>Video Output Overlay (OSD) Interface, <xref
	    linkend="osd" />.</para>
      </listitem>
	<listitem>
	<para><constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY</constant>,
	&v4l2-buf-type;, <xref linkend="v4l2-buf-type" />.</para>
      </listitem>
      <listitem>
	<para><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant>,
&VIDIOC-QUERYCAP; ioctl, <xref linkend="device-capabilities" />.</para>
      </listitem>
      <listitem>
	<para>&VIDIOC-ENUM-FRAMESIZES; and
&VIDIOC-ENUM-FRAMEINTERVALS; ioctls.</para>
      </listitem>
      <listitem>
	<para>&VIDIOC-G-ENC-INDEX; ioctl.</para>
      </listitem>
      <listitem>
	<para>&VIDIOC-ENCODER-CMD; and &VIDIOC-TRY-ENCODER-CMD;
ioctls.</para>
      </listitem>
      <listitem>
	<para>&VIDIOC-DBG-G-REGISTER; and &VIDIOC-DBG-S-REGISTER;
ioctls.</para>
      </listitem>
      <listitem>
	<para>&VIDIOC-DBG-G-CHIP-IDENT; ioctl.</para>
      </listitem>
    </itemizedlist>
  </section>

  <section id="obsolete">
    <title>Obsolete API Elements</title>

    <para>The following V4L2 API elements were superseded by new
interfaces and should not be implemented in new drivers.</para>

    <itemizedlist>
      <listitem>
	<para><constant>VIDIOC_G_MPEGCOMP</constant> and
<constant>VIDIOC_S_MPEGCOMP</constant> ioctls. Use Extended Controls,
<xref linkend="extended-controls" />.</para>
      </listitem>
    </itemizedlist>
  </section>

  <!--
Local Variables:
mode: sgml
sgml-parent-document: "v4l2.sgml"
indent-tabs-mode: nil
End:
  -->
OpenPOWER on IntegriCloud