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 programming interface layer above different underly-
     ing video hardware drivers.  The video layer provides a Video4Linux2 compatible API.  A number of ioctl(2) commands are supported controlling
     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 streaming 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 supported 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 recommended.

     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 available, 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 support writing, overlay, VBI, tuner, audio, radio,
     or asyncio.

BSD
								   March 5, 2011							       BSD