summaryrefslogtreecommitdiffstats
path: root/libavformat/gifdec.c
blob: 48bd603dd0a5d2aa40eac16a0d80752c2347b439 (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
/*
 * GIF demuxer
 * Copyright (c) 2012 Vitaliy E Sugrobov
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * GIF demuxer.
 */

#include "avformat.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "libavcodec/gif.h"

typedef struct GIFDemuxContext {
    const AVClass *class;
    /**
     * Time span in hundredths of second before
     * the next frame should be drawn on screen.
     */
    int delay;
    /**
     * Minimum allowed delay between frames in hundredths of
     * second. Values below this threshold considered to be
     * invalid and set to value of default_delay.
     */
    int min_delay;
    int max_delay;
    int default_delay;

    /**
     * loop options
     */
    int total_iter;
    int iter_count;
    int ignore_loop;

    int nb_frames;
    int last_duration;
} GIFDemuxContext;

/**
 * Major web browsers display gifs at ~10-15fps when rate
 * is not explicitly set or have too low values. We assume default rate to be 10.
 * Default delay = 100hundredths of second / 10fps = 10hos per frame.
 */
#define GIF_DEFAULT_DELAY   10
/**
 * By default delay values less than this threshold considered to be invalid.
 */
#define GIF_MIN_DELAY       2

static int gif_probe(AVProbeData *p)
{
    /* check magick */
    if (memcmp(p->buf, gif87a_sig, 6) && memcmp(p->buf, gif89a_sig, 6))
        return 0;

    /* width or height contains zero? */
    if (!AV_RL16(&p->buf[6]) || !AV_RL16(&p->buf[8]))
        return 0;

    return AVPROBE_SCORE_MAX;
}

static int resync(AVIOContext *pb)
{
    int i;
    for (i = 0; i < 6; i++) {
        int b = avio_r8(pb);
        if (b != gif87a_sig[i] && b != gif89a_sig[i])
            i = -(b != 'G');
        if (avio_feof(pb))
            return AVERROR_EOF;
    }
    return 0;
}

static int gif_read_header(AVFormatContext *s)
{
    GIFDemuxContext *gdc = s->priv_data;
    AVIOContext     *pb  = s->pb;
    AVStream        *st;
    int width, height, ret;

    if ((ret = resync(pb)) < 0)
        return ret;

    gdc->delay  = gdc->default_delay;
    width  = avio_rl16(pb);
    height = avio_rl16(pb);

    if (width == 0 || height == 0)
        return AVERROR_INVALIDDATA;

    st = avformat_new_stream(s, NULL);
    if (!st)
        return AVERROR(ENOMEM);

    /* GIF format operates with time in "hundredths of second",
     * therefore timebase is 1/100 */
    avpriv_set_pts_info(st, 64, 1, 100);
    st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
    st->codec->codec_id   = AV_CODEC_ID_GIF;
    st->codec->width      = width;
    st->codec->height     = height;

    /* jump to start because gif decoder needs header data too */
    if (avio_seek(pb, 0, SEEK_SET) != 0)
        return AVERROR(EIO);

    return 0;
}

static int gif_skip_subblocks(AVIOContext *pb)
{
    int sb_size, ret = 0;

    while (0x00 != (sb_size = avio_r8(pb))) {
        if ((ret = avio_skip(pb, sb_size)) < 0)
            return ret;
    }

    return ret;
}

static int gif_read_ext(AVFormatContext *s)
{
    GIFDemuxContext *gdc = s->priv_data;
    AVIOContext *pb = s->pb;
    int sb_size, ext_label = avio_r8(pb);
    int ret;

    if (ext_label == GIF_GCE_EXT_LABEL) {
        if ((sb_size = avio_r8(pb)) < 4) {
            av_log(s, AV_LOG_FATAL, "Graphic Control Extension block's size less than 4.\n");
            return AVERROR_INVALIDDATA;
        }

        /* skip packed fields */
        if ((ret = avio_skip(pb, 1)) < 0)
            return ret;

        gdc->delay = avio_rl16(pb);

        if (gdc->delay < gdc->min_delay)
            gdc->delay = gdc->default_delay;
        gdc->delay = FFMIN(gdc->delay, gdc->max_delay);

        /* skip the rest of the Graphic Control Extension block */
        if ((ret = avio_skip(pb, sb_size - 3)) < 0 )
            return ret;
    } else if (ext_label == GIF_APP_EXT_LABEL) {
        uint8_t data[256];

        sb_size = avio_r8(pb);
        ret = avio_read(pb, data, sb_size);
        if (ret < 0 || !sb_size)
            return ret;

        if (sb_size == strlen(NETSCAPE_EXT_STR)) {
            sb_size = avio_r8(pb);
            ret = avio_read(pb, data, sb_size);
            if (ret < 0 || !sb_size)
                return ret;

            if (sb_size == 3 && data[0] == 1) {
                gdc->total_iter = AV_RL16(data+1);

                if (gdc->total_iter == 0)
                    gdc->total_iter = -1;
            }
        }
    }

    if ((ret = gif_skip_subblocks(pb)) < 0)
        return ret;

    return 0;
}

static int gif_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    GIFDemuxContext *gdc = s->priv_data;
    AVIOContext *pb = s->pb;
    int packed_fields, block_label, ct_size,
        keyframe, frame_parsed = 0, ret;
    int64_t frame_start = avio_tell(pb), frame_end;
    unsigned char buf[6];

    if ((ret = avio_read(pb, buf, 6)) == 6) {
        keyframe = memcmp(buf, gif87a_sig, 6) == 0 ||
                   memcmp(buf, gif89a_sig, 6) == 0;
    } else if (ret < 0) {
        return ret;
    } else {
        keyframe = 0;
    }

    if (keyframe) {
parse_keyframe:
        /* skip 2 bytes of width and 2 of height */
        if ((ret = avio_skip(pb, 4)) < 0)
            return ret;

        packed_fields = avio_r8(pb);

        /* skip 1 byte of Background Color Index and 1 byte of Pixel Aspect Ratio */
        if ((ret = avio_skip(pb, 2)) < 0)
            return ret;

        /* global color table presence */
        if (packed_fields & 0x80) {
            ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));

            if ((ret = avio_skip(pb, ct_size)) < 0)
                return ret;
        }
    } else {
        avio_seek(pb, -ret, SEEK_CUR);
        ret = AVERROR_EOF;
    }

    while (GIF_TRAILER != (block_label = avio_r8(pb)) && !avio_feof(pb)) {
        if (block_label == GIF_EXTENSION_INTRODUCER) {
            if ((ret = gif_read_ext (s)) < 0 )
                goto resync;
        } else if (block_label == GIF_IMAGE_SEPARATOR) {
            /* skip to last byte of Image Descriptor header */
            if ((ret = avio_skip(pb, 8)) < 0)
                return ret;

            packed_fields = avio_r8(pb);

            /* local color table presence */
            if (packed_fields & 0x80) {
                ct_size = 3 * (1 << ((packed_fields & 0x07) + 1));

                if ((ret = avio_skip(pb, ct_size)) < 0)
                    return ret;
            }

            /* read LZW Minimum Code Size */
            if (avio_r8(pb) < 1) {
                av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >= 1\n");
                goto resync;
            }

            if ((ret = gif_skip_subblocks(pb)) < 0)
                goto resync;

            frame_end = avio_tell(pb);

            if (avio_seek(pb, frame_start, SEEK_SET) != frame_start)
                return AVERROR(EIO);

            ret = av_get_packet(pb, pkt, frame_end - frame_start);
            if (ret < 0)
                return ret;

            if (keyframe)
                pkt->flags |= AV_PKT_FLAG_KEY;

            pkt->stream_index = 0;
            pkt->duration = gdc->delay;

            gdc->nb_frames ++;
            gdc->last_duration = pkt->duration;

            /* Graphic Control Extension's scope is single frame.
             * Remove its influence. */
            gdc->delay = gdc->default_delay;
            frame_parsed = 1;

            break;
        } else {
            av_log(s, AV_LOG_ERROR, "invalid block label\n");
resync:
            if (!keyframe)
                avio_seek(pb, frame_start, SEEK_SET);
            if ((ret = resync(pb)) < 0)
                return ret;
            frame_start = avio_tell(pb) - 6;
            keyframe = 1;
            goto parse_keyframe;
        }
    }

    if ((ret >= 0 && !frame_parsed) || ret == AVERROR_EOF) {
        if (gdc->nb_frames == 1) {
            s->streams[0]->r_frame_rate = (AVRational) {100, gdc->last_duration};
        }
        /* This might happen when there is no image block
         * between extension blocks and GIF_TRAILER or EOF */
        if (!gdc->ignore_loop && (block_label == GIF_TRAILER || avio_feof(pb))
            && (gdc->total_iter < 0 || ++gdc->iter_count < gdc->total_iter))
            return avio_seek(pb, 0, SEEK_SET);
        return AVERROR_EOF;
    } else
        return ret;
}

static const AVOption options[] = {
    { "min_delay"    , "minimum valid delay between frames (in hundredths of second)", offsetof(GIFDemuxContext, min_delay)    , AV_OPT_TYPE_INT, {.i64 = GIF_MIN_DELAY}    , 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
    { "max_gif_delay", "maximum valid delay between frames (in hundredths of seconds)", offsetof(GIFDemuxContext, max_delay)   , AV_OPT_TYPE_INT, {.i64 = 65535}            , 0, 65535   , AV_OPT_FLAG_DECODING_PARAM },
    { "default_delay", "default delay between frames (in hundredths of second)"      , offsetof(GIFDemuxContext, default_delay), AV_OPT_TYPE_INT, {.i64 = GIF_DEFAULT_DELAY}, 0, 100 * 60, AV_OPT_FLAG_DECODING_PARAM },
    { "ignore_loop"  , "ignore loop setting (netscape extension)"                    , offsetof(GIFDemuxContext, ignore_loop)  , AV_OPT_TYPE_BOOL,{.i64 = 1}                , 0,        1, AV_OPT_FLAG_DECODING_PARAM },
    { NULL },
};

static const AVClass demuxer_class = {
    .class_name = "GIF demuxer",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
    .category   = AV_CLASS_CATEGORY_DEMUXER,
};

AVInputFormat ff_gif_demuxer = {
    .name           = "gif",
    .long_name      = NULL_IF_CONFIG_SMALL("CompuServe Graphics Interchange Format (GIF)"),
    .priv_data_size = sizeof(GIFDemuxContext),
    .read_probe     = gif_probe,
    .read_header    = gif_read_header,
    .read_packet    = gif_read_packet,
    .flags          = AVFMT_GENERIC_INDEX,
    .priv_class     = &demuxer_class,
};
OpenPOWER on IntegriCloud