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Diffstat (limited to 'Documentation/DocBook/media/v4l/common.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/common.xml | 412 |
1 files changed, 157 insertions, 255 deletions
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml index 1ddf354..71f6bf9 100644 --- a/Documentation/DocBook/media/v4l/common.xml +++ b/Documentation/DocBook/media/v4l/common.xml @@ -38,70 +38,41 @@ the basic concepts applicable to all devices.</para> <para>V4L2 drivers are implemented as kernel modules, loaded manually by the system administrator or automatically when a device is -first opened. The driver modules plug into the "videodev" kernel +first discovered. The driver modules plug into the "videodev" kernel module. It provides helper functions and a common application interface specified in this document.</para> <para>Each driver thus loaded registers one or more device nodes -with major number 81 and a minor number between 0 and 255. Assigning -minor numbers to V4L2 devices is entirely up to the system administrator, -this is primarily intended to solve conflicts between devices.<footnote> - <para>Access permissions are associated with character -device special files, hence we must ensure device numbers cannot -change with the module load order. To this end minor numbers are no -longer automatically assigned by the "videodev" module as in V4L but -requested by the driver. The defaults will suffice for most people -unless two drivers compete for the same minor numbers.</para> - </footnote> The module options to select minor numbers are named -after the device special file with a "_nr" suffix. For example "video_nr" -for <filename>/dev/video</filename> video capture devices. The number is -an offset to the base minor number associated with the device type. -<footnote> - <para>In earlier versions of the V4L2 API the module options -where named after the device special file with a "unit_" prefix, expressing -the minor number itself, not an offset. Rationale for this change is unknown. -Lastly the naming and semantics are just a convention among driver writers, -the point to note is that minor numbers are not supposed to be hardcoded -into drivers.</para> - </footnote> When the driver supports multiple devices of the same -type more than one minor number can be assigned, separated by commas: -<informalexample> +with major number 81 and a minor number between 0 and 255. Minor numbers +are allocated dynamically unless the kernel is compiled with the kernel +option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers are +allocated in ranges depending on the device node type (video, radio, etc.).</para> + + <para>Many drivers support "video_nr", "radio_nr" or "vbi_nr" +module options to select specific video/radio/vbi node numbers. This allows +the user to request that the device node is named e.g. /dev/video5 instead +of leaving it to chance. When the driver supports multiple devices of the same +type more than one device node number can be assigned, separated by commas: + <informalexample> <screen> -> insmod mydriver.o video_nr=0,1 radio_nr=0,1</screen> +> modprobe mydriver video_nr=0,1 radio_nr=0,1</screen> </informalexample></para> <para>In <filename>/etc/modules.conf</filename> this may be written as: <informalexample> <screen> -alias char-major-81-0 mydriver -alias char-major-81-1 mydriver -alias char-major-81-64 mydriver <co id="alias" /> -options mydriver video_nr=0,1 radio_nr=0,1 <co id="options" /> +options mydriver video_nr=0,1 radio_nr=0,1 </screen> - <calloutlist> - <callout arearefs="alias"> - <para>When an application attempts to open a device -special file with major number 81 and minor number 0, 1, or 64, load -"mydriver" (and the "videodev" module it depends upon).</para> - </callout> - <callout arearefs="options"> - <para>Register the first two video capture devices with -minor number 0 and 1 (base number is 0), the first two radio device -with minor number 64 and 65 (base 64).</para> - </callout> - </calloutlist> - </informalexample> When no minor number is given as module -option the driver supplies a default. <xref linkend="devices" /> -recommends the base minor numbers to be used for the various device -types. Obviously minor numbers must be unique. When the number is -already in use the <emphasis>offending device</emphasis> will not be -registered. <!-- Blessed by Linus Torvalds on -linux-kernel@vger.kernel.org, 2002-11-20. --></para> - - <para>By convention system administrators create various -character device special files with these major and minor numbers in -the <filename>/dev</filename> directory. The names recommended for the -different V4L2 device types are listed in <xref linkend="devices" />. + </informalexample> When no device node number is given as module +option the driver supplies a default.</para> + + <para>Normally udev will create the device nodes in /dev automatically +for you. If udev is not installed, then you need to enable the +CONFIG_VIDEO_FIXED_MINOR_RANGES kernel option in order to be able to correctly +relate a minor number to a device node number. I.e., you need to be certain +that minor number 5 maps to device node name video5. With this kernel option +different device types have different minor number ranges. These ranges are +listed in <xref linkend="devices" />. </para> <para>The creation of character special files (with @@ -110,85 +81,66 @@ devices cannot be opened by major and minor number. That means applications cannot <emphasis>reliable</emphasis> scan for loaded or installed drivers. The user must enter a device name, or the application can try the conventional device names.</para> - - <para>Under the device filesystem (devfs) the minor number -options are ignored. V4L2 drivers (or by proxy the "videodev" module) -automatically create the required device files in the -<filename>/dev/v4l</filename> directory using the conventional device -names above.</para> </section> <section id="related"> <title>Related Devices</title> - <para>Devices can support several related functions. For example -video capturing, video overlay and VBI capturing are related because -these functions share, amongst other, the same video input and tuner -frequency. V4L and earlier versions of V4L2 used the same device name -and minor number for video capturing and overlay, but different ones -for VBI. Experience showed this approach has several problems<footnote> - <para>Given a device file name one cannot reliable find -related devices. For once names are arbitrary and in a system with -multiple devices, where only some support VBI capturing, a -<filename>/dev/video2</filename> is not necessarily related to -<filename>/dev/vbi2</filename>. The V4L -<constant>VIDIOCGUNIT</constant> ioctl would require a search for a -device file with a particular major and minor number.</para> - </footnote>, and to make things worse the V4L videodev module -used to prohibit multiple opens of a device.</para> - - <para>As a remedy the present version of the V4L2 API relaxed the -concept of device types with specific names and minor numbers. For -compatibility with old applications drivers must still register different -minor numbers to assign a default function to the device. But if related -functions are supported by the driver they must be available under all -registered minor numbers. The desired function can be selected after -opening the device as described in <xref linkend="devices" />.</para> - - <para>Imagine a driver supporting video capturing, video -overlay, raw VBI capturing, and FM radio reception. It registers three -devices with minor number 0, 64 and 224 (this numbering scheme is -inherited from the V4L API). Regardless if -<filename>/dev/video</filename> (81, 0) or -<filename>/dev/vbi</filename> (81, 224) is opened the application can -select any one of the video capturing, overlay or VBI capturing -functions. Without programming (e. g. reading from the device -with <application>dd</application> or <application>cat</application>) -<filename>/dev/video</filename> captures video images, while -<filename>/dev/vbi</filename> captures raw VBI data. -<filename>/dev/radio</filename> (81, 64) is invariable a radio device, -unrelated to the video functions. Being unrelated does not imply the -devices can be used at the same time, however. The &func-open; -function may very well return an &EBUSY;.</para> + <para>Devices can support several functions. For example +video capturing, VBI capturing and radio support.</para> + + <para>The V4L2 API creates different nodes for each of these functions.</para> + + <para>The V4L2 API was designed with the idea that one device node could support +all functions. However, in practice this never worked: this 'feature' +was never used by applications and many drivers did not support it and if +they did it was certainly never tested. In addition, switching a device +node between different functions only works when using the streaming I/O +API, not with the read()/write() API.</para> + + <para>Today each device node supports just one function.</para> <para>Besides video input or output the hardware may also support audio sampling or playback. If so, these functions are -implemented as OSS or ALSA PCM devices and eventually OSS or ALSA -audio mixer. The V4L2 API makes no provisions yet to find these -related devices. If you have an idea please write to the linux-media -mailing list: &v4l-ml;.</para> +implemented as ALSA PCM devices with optional ALSA audio mixer +devices.</para> + + <para>One problem with all these devices is that the V4L2 API +makes no provisions to find these related devices. Some really +complex devices use the Media Controller (see <xref linkend="media_controller" />) +which can be used for this purpose. But most drivers do not use it, +and while some code exists that uses sysfs to discover related devices +(see libmedia_dev in the <ulink url="http://git.linuxtv.org/v4l-utils/">v4l-utils</ulink> +git repository), there is no library yet that can provide a single API towards +both Media Controller-based devices and devices that do not use the Media Controller. +If you want to work on this please write to the linux-media mailing list: &v4l-ml;.</para> </section> <section> <title>Multiple Opens</title> - <para>In general, V4L2 devices can be opened more than once. + <para>V4L2 devices can be opened more than once.<footnote><para> +There are still some old and obscure drivers that have not been updated to +allow for multiple opens. This implies that for such drivers &func-open; can +return an &EBUSY; when the device is already in use.</para></footnote> When this is supported by the driver, users can for example start a "panel" application to change controls like brightness or audio volume, while another application captures video and audio. In other words, panel -applications are comparable to an OSS or ALSA audio mixer application. -When a device supports multiple functions like capturing and overlay -<emphasis>simultaneously</emphasis>, multiple opens allow concurrent -use of the device by forked processes or specialized applications.</para> - - <para>Multiple opens are optional, although drivers should -permit at least concurrent accesses without data exchange, &ie; panel -applications. This implies &func-open; can return an &EBUSY; when the -device is already in use, as well as &func-ioctl; functions initiating -data exchange (namely the &VIDIOC-S-FMT; ioctl), and the &func-read; -and &func-write; functions.</para> - - <para>Mere opening a V4L2 device does not grant exclusive +applications are comparable to an ALSA audio mixer application. +Just opening a V4L2 device should not change the state of the device.<footnote> +<para>Unfortunately, opening a radio device often switches the state of the +device to radio mode in many drivers. This behavior should be fixed eventually +as it violates the V4L2 specification.</para></footnote></para> + + <para>Once an application has allocated the memory buffers needed for +streaming data (by calling the &VIDIOC-REQBUFS; or &VIDIOC-CREATE-BUFS; ioctls, +or implicitly by calling the &func-read; or &func-write; functions) that +application (filehandle) becomes the owner of the device. It is no longer +allowed to make changes that would affect the buffer sizes (e.g. by calling +the &VIDIOC-S-FMT; ioctl) and other applications are no longer allowed to allocate +buffers or start or stop streaming. The &EBUSY; will be returned instead.</para> + + <para>Merely opening a V4L2 device does not grant exclusive access.<footnote> <para>Drivers could recognize the <constant>O_EXCL</constant> open flag. Presently this is not required, @@ -206,12 +158,7 @@ additional access privileges using the priority mechanism described in <para>V4L2 drivers should not support multiple applications reading or writing the same data stream on a device by copying buffers, time multiplexing or similar means. This is better handled by -a proxy application in user space. When the driver supports stream -sharing anyway it must be implemented transparently. The V4L2 API does -not specify how conflicts are solved. <!-- For example O_EXCL when the -application does not want to be preempted, PROT_READ mmapped buffers -which can be mapped twice, what happens when image formats do not -match etc.--></para> +a proxy application in user space.</para> </section> <section> @@ -240,15 +187,15 @@ methods</link> supported by the device.</para> <para>Starting with kernel version 3.1, VIDIOC-QUERYCAP will return the V4L2 API version used by the driver, with generally matches the Kernel version. -There's no need of using &VIDIOC-QUERYCAP; to check if an specific ioctl is -supported, the V4L2 core now returns ENOIOCTLCMD if a driver doesn't provide +There's no need of using &VIDIOC-QUERYCAP; to check if a specific ioctl is +supported, the V4L2 core now returns ENOTTY if a driver doesn't provide support for an ioctl.</para> <para>Other features can be queried by calling the respective ioctl, for example &VIDIOC-ENUMINPUT; to learn about the number, types and names of video connectors on the device. Although abstraction is a major objective of this API, the -ioctl also allows driver specific applications to reliable identify +&VIDIOC-QUERYCAP; ioctl also allows driver specific applications to reliably identify the driver.</para> <para>All V4L2 drivers must support @@ -278,9 +225,7 @@ Applications requiring a different priority will usually call the &VIDIOC-QUERYCAP; ioctl.</para> <para>Ioctls changing driver properties, such as &VIDIOC-S-INPUT;, -return an &EBUSY; after another application obtained higher priority. -An event mechanism to notify applications about asynchronous property -changes has been proposed but not added yet.</para> +return an &EBUSY; after another application obtained higher priority.</para> </section> <section id="video"> @@ -288,9 +233,9 @@ changes has been proposed but not added yet.</para> <para>Video inputs and outputs are physical connectors of a device. These can be for example RF connectors (antenna/cable), CVBS -a.k.a. Composite Video, S-Video or RGB connectors. Only video and VBI -capture devices have inputs, output devices have outputs, at least one -each. Radio devices have no video inputs or outputs.</para> +a.k.a. Composite Video, S-Video or RGB connectors. Video and VBI +capture devices have inputs. Video and VBI output devices have outputs, +at least one each. Radio devices have no video inputs or outputs.</para> <para>To learn about the number and attributes of the available inputs and outputs applications can enumerate them with the @@ -299,30 +244,13 @@ available inputs and outputs applications can enumerate them with the ioctl also contains signal status information applicable when the current video input is queried.</para> - <para>The &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; ioctl return the + <para>The &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; ioctls return the index of the current video input or output. To select a different input or output applications call the &VIDIOC-S-INPUT; and -&VIDIOC-S-OUTPUT; ioctl. Drivers must implement all the input ioctls +&VIDIOC-S-OUTPUT; ioctls. Drivers must implement all the input ioctls when the device has one or more inputs, all the output ioctls when the device has one or more outputs.</para> - <!-- - <figure id=io-tree> - <title>Input and output enumeration is the root of most device properties.</title> - <mediaobject> - <imageobject> - <imagedata fileref="links.pdf" format="ps" /> - </imageobject> - <imageobject> - <imagedata fileref="links.gif" format="gif" /> - </imageobject> - <textobject> - <phrase>Links between various device property structures.</phrase> - </textobject> - </mediaobject> - </figure> - --> - <example> <title>Information about the current video input</title> @@ -330,20 +258,20 @@ device has one or more outputs.</para> &v4l2-input; input; int index; -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); input.index = index; -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUMINPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUMINPUT"); + exit(EXIT_FAILURE); } -printf ("Current input: %s\n", input.name); +printf("Current input: %s\n", input.name); </programlisting> </example> @@ -355,9 +283,9 @@ int index; index = 0; -if (-1 == ioctl (fd, &VIDIOC-S-INPUT;, &index)) { - perror ("VIDIOC_S_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-INPUT;, &index)) { + perror("VIDIOC_S_INPUT"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -397,7 +325,7 @@ available inputs and outputs applications can enumerate them with the also contains signal status information applicable when the current audio input is queried.</para> - <para>The &VIDIOC-G-AUDIO; and &VIDIOC-G-AUDOUT; ioctl report + <para>The &VIDIOC-G-AUDIO; and &VIDIOC-G-AUDOUT; ioctls report the current audio input and output, respectively. Note that, unlike &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; these ioctls return a structure as <constant>VIDIOC_ENUMAUDIO</constant> and @@ -408,11 +336,11 @@ applications call the &VIDIOC-S-AUDIO; ioctl. To select an audio output (which presently has no changeable properties) applications call the &VIDIOC-S-AUDOUT; ioctl.</para> - <para>Drivers must implement all input ioctls when the device -has one or more inputs, all output ioctls when the device has one -or more outputs. When the device has any audio inputs or outputs the -driver must set the <constant>V4L2_CAP_AUDIO</constant> flag in the -&v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl.</para> + <para>Drivers must implement all audio input ioctls when the device +has multiple selectable audio inputs, all audio output ioctls when the +device has multiple selectable audio outputs. When the device has any +audio inputs or outputs the driver must set the <constant>V4L2_CAP_AUDIO</constant> +flag in the &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl.</para> <example> <title>Information about the current audio input</title> @@ -420,14 +348,14 @@ driver must set the <constant>V4L2_CAP_AUDIO</constant> flag in the <programlisting> &v4l2-audio; audio; -memset (&audio, 0, sizeof (audio)); +memset(&audio, 0, sizeof(audio)); -if (-1 == ioctl (fd, &VIDIOC-G-AUDIO;, &audio)) { - perror ("VIDIOC_G_AUDIO"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-AUDIO;, &audio)) { + perror("VIDIOC_G_AUDIO"); + exit(EXIT_FAILURE); } -printf ("Current input: %s\n", audio.name); +printf("Current input: %s\n", audio.name); </programlisting> </example> @@ -437,13 +365,13 @@ printf ("Current input: %s\n", audio.name); <programlisting> &v4l2-audio; audio; -memset (&audio, 0, sizeof (audio)); /* clear audio.mode, audio.reserved */ +memset(&audio, 0, sizeof(audio)); /* clear audio.mode, audio.reserved */ audio.index = 0; -if (-1 == ioctl (fd, &VIDIOC-S-AUDIO;, &audio)) { - perror ("VIDIOC_S_AUDIO"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-AUDIO;, &audio)) { + perror("VIDIOC_S_AUDIO"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -468,7 +396,7 @@ the tuner.</para> video inputs.</para> <para>To query and change tuner properties applications use the -&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctl, respectively. The +&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctls, respectively. The &v4l2-tuner; returned by <constant>VIDIOC_G_TUNER</constant> also contains signal status information applicable when the tuner of the current video or radio input is queried. Note that @@ -533,7 +461,7 @@ standards or variations of standards. Each video input and output may support another set of standards. This set is reported by the <structfield>std</structfield> field of &v4l2-input; and &v4l2-output; returned by the &VIDIOC-ENUMINPUT; and -&VIDIOC-ENUMOUTPUT; ioctl, respectively.</para> +&VIDIOC-ENUMOUTPUT; ioctls, respectively.</para> <para>V4L2 defines one bit for each analog video standard currently in use worldwide, and sets aside bits for driver defined @@ -564,28 +492,10 @@ automatically.</para> <para>To query and select the standard used by the current video input or output applications call the &VIDIOC-G-STD; and &VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis> -standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote> - <para>An alternative to the current scheme is to use pointers -to indices as arguments of <constant>VIDIOC_G_STD</constant> and -<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and -&v4l2-output; <structfield>std</structfield> field would be a set of -indices like <structfield>audioset</structfield>.</para> - <para>Indices are consistent with the rest of the API -and identify the standard unambiguously. In the present scheme of -things an enumerated standard is looked up by &v4l2-std-id;. Now the -standards supported by the inputs of a device can overlap. Just -assume the tuner and composite input in the example above both -exist on a device. An enumeration of "PAL-B/G", "PAL-H/I" suggests -a choice which does not exist. We cannot merge or omit sets, because -applications would be unable to find the standards reported by -<constant>VIDIOC_G_STD</constant>. That leaves separate enumerations -for each input. Also selecting a standard by &v4l2-std-id; can be -ambiguous. Advantage of this method is that applications need not -identify the standard indirectly, after enumerating.</para><para>So in -summary, the lookup itself is unavoidable. The difference is only -whether the lookup is necessary to find an enumerated standard or to -switch to a standard by &v4l2-std-id;.</para> - </footnote> Drivers must implement all video standard ioctls +standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the +parameter of all these ioctls is a pointer to a &v4l2-std-id; type +(a standard set), <emphasis>not</emphasis> an index into the standard +enumeration. Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs.</para> <para>Special rules apply to devices such as USB cameras where the notion of video @@ -604,17 +514,10 @@ to zero and the <constant>VIDIOC_G_STD</constant>, <constant>VIDIOC_S_STD</constant>, <constant>VIDIOC_QUERYSTD</constant> and <constant>VIDIOC_ENUMSTD</constant> ioctls shall return the -&ENOTTY;.<footnote> - <para>See <xref linkend="buffer" /> for a rationale.</para> +&ENOTTY; or the &EINVAL;.</para> <para>Applications can make use of the <xref linkend="input-capabilities" /> and <xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls -are available for the device.</para> - - <para>See <xref linkend="buffer" /> for a rationale. Probably -even USB cameras follow some well known video standard. It might have -been better to explicitly indicate elsewhere if a device cannot live -up to normal expectations, instead of this exception.</para> - </footnote></para> +can be used with the given input or output.</para> <example> <title>Information about the current video standard</title> @@ -623,22 +526,22 @@ up to normal expectations, instead of this exception.</para> &v4l2-std-id; std_id; &v4l2-standard; standard; -if (-1 == ioctl (fd, &VIDIOC-G-STD;, &std_id)) { +if (-1 == ioctl(fd, &VIDIOC-G-STD;, &std_id)) { /* Note when VIDIOC_ENUMSTD always returns ENOTTY this is no video device or it falls under the USB exception, and VIDIOC_G_STD returning ENOTTY is no error. */ - perror ("VIDIOC_G_STD"); - exit (EXIT_FAILURE); + perror("VIDIOC_G_STD"); + exit(EXIT_FAILURE); } -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & std_id) { - printf ("Current video standard: %s\n", standard.name); - exit (EXIT_SUCCESS); + printf("Current video standard: %s\n", standard.name); + exit(EXIT_SUCCESS); } standard.index++; @@ -648,8 +551,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { empty unless this device falls under the USB exception. */ if (errno == EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -662,26 +565,26 @@ input</title> &v4l2-input; input; &v4l2-standard; standard; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } -printf ("Current input %s supports:\n", input.name); +printf("Current input %s supports:\n", input.name); -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & input.std) - printf ("%s\n", standard.name); + printf("%s\n", standard.name); standard.index++; } @@ -690,8 +593,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { empty unless this device falls under the USB exception. */ if (errno != EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -703,21 +606,21 @@ if (errno != EINVAL || standard.index == 0) { &v4l2-input; input; &v4l2-std-id; std_id; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } if (0 == (input.std & V4L2_STD_PAL_BG)) { - fprintf (stderr, "Oops. B/G PAL is not supported.\n"); - exit (EXIT_FAILURE); + fprintf(stderr, "Oops. B/G PAL is not supported.\n"); + exit(EXIT_FAILURE); } /* Note this is also supposed to work when only B @@ -725,9 +628,9 @@ if (0 == (input.std & V4L2_STD_PAL_BG)) { std_id = V4L2_STD_PAL_BG; -if (-1 == ioctl (fd, &VIDIOC-S-STD;, &std_id)) { - perror ("VIDIOC_S_STD"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-STD;, &std_id)) { + perror("VIDIOC_S_STD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -740,26 +643,25 @@ corresponding video timings. Today there are many more different hardware interf such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry video signals and there is a need to extend the API to select the video timings for these interfaces. Since it is not possible to extend the &v4l2-std-id; due to -the limited bits available, a new set of IOCTLs was added to set/get video timings at -the input and output: </para><itemizedlist> - <listitem> - <para>DV Timings: This will allow applications to define detailed -video timings for the interface. This includes parameters such as width, height, -polarities, frontporch, backporch etc. The <filename>linux/v4l2-dv-timings.h</filename> +the limited bits available, a new set of ioctls was added to set/get video timings at +the input and output.</para> + + <para>These ioctls deal with the detailed digital video timings that define +each video format. This includes parameters such as the active video width and height, +signal polarities, frontporches, backporches, sync widths etc. The <filename>linux/v4l2-dv-timings.h</filename> header can be used to get the timings of the formats in the <xref linkend="cea861" /> and <xref linkend="vesadmt" /> standards. </para> - </listitem> - </itemizedlist> - <para>To enumerate and query the attributes of the DV timings supported by a device, + + <para>To enumerate and query the attributes of the DV timings supported by a device applications use the &VIDIOC-ENUM-DV-TIMINGS; and &VIDIOC-DV-TIMINGS-CAP; ioctls. - To set DV timings for the device, applications use the + To set DV timings for the device applications use the &VIDIOC-S-DV-TIMINGS; ioctl and to get current DV timings they use the &VIDIOC-G-DV-TIMINGS; ioctl. To detect the DV timings as seen by the video receiver applications use the &VIDIOC-QUERY-DV-TIMINGS; ioctl.</para> <para>Applications can make use of the <xref linkend="input-capabilities" /> and -<xref linkend="output-capabilities"/> flags to decide what ioctls are available to set the -video timings for the device.</para> +<xref linkend="output-capabilities"/> flags to determine whether the digital video ioctls +can be used with the given input or output.</para> </section> &sub-controls; |
