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diff --git a/Documentation/DocBook/v4l/compat.xml b/Documentation/DocBook/v4l/compat.xml new file mode 100644 index 00000000000..4d1902a54d6 --- /dev/null +++ b/Documentation/DocBook/v4l/compat.xml @@ -0,0 +1,2457 @@ + <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 × 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 |