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diff --git a/Documentation/DocBook/media/v4l/dev-capture.xml b/Documentation/DocBook/media/v4l/dev-capture.xml deleted file mode 100644 index e1c5f9406d6a..000000000000 --- a/Documentation/DocBook/media/v4l/dev-capture.xml +++ /dev/null @@ -1,110 +0,0 @@ - <title>Video Capture Interface</title> - - <para>Video capture devices sample an analog video signal and store -the digitized images in memory. Today nearly all devices can capture -at full 25 or 30 frames/second. With this interface applications can -control the capture process and move images from the driver into user -space.</para> - - <para>Conventionally V4L2 video capture devices are accessed through -character device special files named <filename>/dev/video</filename> -and <filename>/dev/video0</filename> to -<filename>/dev/video63</filename> with major number 81 and minor -numbers 0 to 63. <filename>/dev/video</filename> is typically a -symbolic link to the preferred video device. Note the same device -files are used for video output devices.</para> - - <section> - <title>Querying Capabilities</title> - - <para>Devices supporting the video capture interface set the -<constant>V4L2_CAP_VIDEO_CAPTURE</constant> or -<constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant> flag in the -<structfield>capabilities</structfield> field of &v4l2-capability; -returned by the &VIDIOC-QUERYCAP; ioctl. As secondary device functions -they may also support the <link linkend="overlay">video overlay</link> -(<constant>V4L2_CAP_VIDEO_OVERLAY</constant>) and the <link -linkend="raw-vbi">raw VBI capture</link> -(<constant>V4L2_CAP_VBI_CAPTURE</constant>) interface. At least one of -the read/write or streaming I/O methods must be supported. Tuners and -audio inputs are optional.</para> - </section> - - <section> - <title>Supplemental Functions</title> - - <para>Video capture devices shall support <link -linkend="audio">audio input</link>, <link -linkend="tuner">tuner</link>, <link linkend="control">controls</link>, -<link linkend="crop">cropping and scaling</link> and <link -linkend="streaming-par">streaming parameter</link> ioctls as needed. -The <link linkend="video">video input</link> and <link -linkend="standard">video standard</link> ioctls must be supported by -all video capture devices.</para> - </section> - - <section> - <title>Image Format Negotiation</title> - - <para>The result of a capture operation is determined by -cropping and image format parameters. The former select an area of the -video picture to capture, the latter how images are stored in memory, -&ie; in RGB or YUV format, the number of bits per pixel or width and -height. Together they also define how images are scaled in the -process.</para> - - <para>As usual these parameters are <emphasis>not</emphasis> reset -at &func-open; time to permit Unix tool chains, programming a device -and then reading from it as if it was a plain file. Well written V4L2 -applications ensure they really get what they want, including cropping -and scaling.</para> - - <para>Cropping initialization at minimum requires to reset the -parameters to defaults. An example is given in <xref -linkend="crop" />.</para> - - <para>To query the current image format applications set the -<structfield>type</structfield> field of a &v4l2-format; to -<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or -<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant> and call the -&VIDIOC-G-FMT; ioctl with a pointer to this structure. Drivers fill -the &v4l2-pix-format; <structfield>pix</structfield> or the -&v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member of the -<structfield>fmt</structfield> union.</para> - - <para>To request different parameters applications set the -<structfield>type</structfield> field of a &v4l2-format; as above and -initialize all fields of the &v4l2-pix-format; -<structfield>vbi</structfield> member of the -<structfield>fmt</structfield> union, or better just modify the -results of <constant>VIDIOC_G_FMT</constant>, and call the -&VIDIOC-S-FMT; ioctl with a pointer to this structure. Drivers may -adjust the parameters and finally return the actual parameters as -<constant>VIDIOC_G_FMT</constant> does.</para> - - <para>Like <constant>VIDIOC_S_FMT</constant> the -&VIDIOC-TRY-FMT; ioctl can be used to learn about hardware limitations -without disabling I/O or possibly time consuming hardware -preparations.</para> - - <para>The contents of &v4l2-pix-format; and &v4l2-pix-format-mplane; -are discussed in <xref linkend="pixfmt" />. See also the specification of the -<constant>VIDIOC_G_FMT</constant>, <constant>VIDIOC_S_FMT</constant> -and <constant>VIDIOC_TRY_FMT</constant> ioctls for details. Video -capture devices must implement both the -<constant>VIDIOC_G_FMT</constant> and -<constant>VIDIOC_S_FMT</constant> ioctl, even if -<constant>VIDIOC_S_FMT</constant> ignores all requests and always -returns default parameters as <constant>VIDIOC_G_FMT</constant> does. -<constant>VIDIOC_TRY_FMT</constant> is optional.</para> - </section> - - <section> - <title>Reading Images</title> - - <para>A video capture device may support the <link -linkend="rw">read() function</link> and/or streaming (<link -linkend="mmap">memory mapping</link> or <link -linkend="userp">user pointer</link>) I/O. See <xref -linkend="io" /> for details.</para> - </section> |