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NetBSD 6.1.5 - man page for video (netbsd section 4)

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VIDEO(4)			   BSD Kernel Interfaces Manual 			 VIDEO(4)

NAME
     video -- device-independent video driver layer

SYNOPSIS
     #include <sys/videoio.h>

DESCRIPTION
     The video driver provides support for various video peripherals.  It provides a uniform pro-
     gramming interface layer above different underlying video hardware drivers.  The video layer
     provides a Video4Linux2 compatible API.  A number of ioctl(2) commands are supported con-
     trolling the device.  See http://v4l2spec.bytesex.org/ for the official V4L2 specification.

     The device file for video operation is /dev/video.

READING VIDEO SAMPLES
     Video data is separated into logical video samples which will typically be one complete
     video frame.  With compressed formats, a video sample may be one logical chunk and not one
     complete frame depending on the compression format.  Video samples may be read from
     /dev/video in one of several different modes.

     In read mode, calls to read(2) will return at most the data of one video sample.  If the
     entire sample is not read, then subsequent reads will return at most the remaining data in
     that video sample.

     Video samples may be mapped into memory with mmap(2).  The driver allocates internal buffers
     for a number of video samples which are mapped into memory.  Initiating this mode requires
     several ioctl(2) commands: VIDIOC_REQBUFS to request the driver reserve buffers,
     VIDIOC_QUERYBUF to query the details of each buffer, mmap(2) to map each buffer into memory,
     VIDIOC_QBUF to queue the buffers for receiving video data, VIDIOC_STREAMON to begin stream-
     ing of video data, and VIDIOC_DQBUF to remove a filled buffer from the queue.  At this point
     the video data from the dequeued buffer is valid.

DEVICE CAPABILITIES
     VIDIOC_QUERYCAP (struct v4l2_capability)
	     This command queries the capabilities of the device.  The first three fields are
	     informational NULL terminated strings filled by the driver: driver describes the
	     driver used by this device, card describes the video capture card or camera, and
	     buf_info represents the bus to which the hardware device is attached.

	     The capabilities field contains a number of flags indicating various features sup-
	     ported by the driver or hardware:

	     V4L2_CAP_VIDEO_CAPTURE
		     support video capturing

	     V4L2_CAP_READWRITE
		     supports the read(2) and/or write(2) mode

	     V4L2_CAP_STREAMING
		     supports mmap(2) mode

	     struct v4l2_capability {
		     uint8_t	     driver[16];
		     uint8_t	     card[32];
		     uint8_t	     bus_info[32];
		     uint32_t	     version;
		     uint32_t	     capabilities;
		     uint32_t	     reserved[4];
	     };

STREAMING INTERFACE
     VIDIOC_REQBUFS (struct v4l2_requestbuffers)
	     This command requests that the driver reserve space for count samples.  type must be
	     set to V4L2_BUF_TYPE_VIDEO_CAPTURE and memory to V4L2_MEMORY_MMAP.  The returned
	     count represents the actual number of samples reserved which may be more or fewer
	     than requested.

	     struct v4l2_requestbuffers {
		     uint32_t		     count;
		     enum v4l2_buf_type      type;
		     enum v4l2_memory	     memory;
		     uint32_t		     reserved[2];
	     };

     VIDIOC_QUERYBUF (struct v4l2_buffer)
	     This command should be called for each buffer in count above.  The fields index,
	     type, and memory must be set to a valid index from 0 to count-1, and the same type
	     and memory as used in VIDIOC_QUERYBUF.  The driver returns m.offset and length.

	     struct v4l2_buffer {
		     uint32_t		     index;
		     enum v4l2_buf_type      type;
		     uint32_t		     bytesused;
		     uint32_t		     flags;
		     enum v4l2_field	     field;
		     struct timeval	     timestamp;
		     struct v4l2_timecode    timecode;
		     uint32_t		     sequence;
		     enum v4l2_memory	     memory;
		     union {
			     uint32_t	     offset;
			     unsigned long   userptr;
		     } m;
		     uint32_t		     length;
		     uint32_t		     input;
		     uint32_t		     reserved;
	     };

     mmap(2)
	     Each buffer must be mapped with a call to mmap(2), passing the length and m.offset
	     values obtained above.  The prot PROT_READ|PROT_WRITE and flags MAP_SHARED are rec-
	     ommended.

     VIDIOC_QBUF (struct v4l2_buffer)
	     This command indicates to the driver that the buffer is ready to receive a video
	     sample.  The following fields must be set: index, set to a valid buffer index from 0
	     to count - 1; type, set to the same type used above; and memory, set to the same
	     memory used above.  Each buffer should be queued with this command.  Order is not
	     important.

     VIDIOC_STREAMON (int)
	     This command starts streaming.  Queued buffers will be filled with data.  select(2)
	     will indicate that a buffer is done and available for reading.

     VIDIOC_DQBUF (struct v4l2_buffer)
	     This command dequeues an available buffer from the driver.  If no buffer is avail-
	     able, it blocks until one is, unless O_NONBLOCK was specified to open(2), in which
	     case it returns EAGAIN.  select(2), or poll(2) prior to initiating any other mode
	     will begin streaming of video for reading with read(2).  In this streaming mode
	     select(2) or poll(2) indicate the availability of a video frame.  Calls to read(2)
	     will return at most the video data of one video sample.  If the entire sample is not
	     read, then subsequent reads will return at most the remaining data in that video
	     sample.

FILES
     /dev/video

SEE ALSO
     auvitek(4), pseye(4), uvideo(4), video(9)

HISTORY
     The video device driver first appeared in NetBSD 5.0.

AUTHORS
     Patrick Mahoney <pat@polycrystal.org>

BUGS
     Does not support the complete V4L2 API.  Only supports the capture interface.  Does not sup-
     port writing, overlay, VBI, tuner, audio, radio, or asyncio.

BSD					  March 5, 2011 				      BSD
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