.\" $NetBSD: video.4,v 1.10.36.1 2023/05/13 11:29:38 martin Exp $ .\" .\" Copyright (c) 2008 Patrick Mahoney .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd March 5, 2011 .Dt VIDEO 4 .Os .Sh NAME .Nm video .Nd device-independent video driver layer .Sh SYNOPSIS .In sys/videoio.h .Sh DESCRIPTION The .Nm driver provides support for various video peripherals. It provides a uniform programming interface layer above different underlying video hardware drivers. The video layer provides a .Tn Video4Linux2 compatible API. A number of .Xr ioctl 2 commands are supported controlling the device. .Pp The device file for video operation is .Pa /dev/video . .Sh 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 .Pa /dev/video in one of several different modes. .Pp In read mode, calls to .Xr 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. .Pp Video samples may be mapped into memory with .Xr mmap 2 . The driver allocates internal buffers for a number of video samples which are mapped into memory. Initiating this mode requires several .Xr ioctl 2 commands: .Dv VIDIOC_REQBUFS to request the driver reserve buffers, .Dv VIDIOC_QUERYBUF to query the details of each buffer, .Xr mmap 2 to map each buffer into memory, .Dv VIDIOC_QBUF to queue the buffers for receiving video data, .Dv VIDIOC_STREAMON to begin streaming of video data, and .Dv VIDIOC_DQBUF to remove a filled buffer from the queue. At this point the video data from the dequeued buffer is valid. .Sh DEVICE CAPABILITIES .Bl -tag -width indent .It Dv 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: .Va driver describes the driver used by this device, .Va card describes the video capture card or camera, and .Va bus_info represents the bus to which the hardware device is attached. .Pp The .Va capabilities field contains a number of flags indicating various features supported by the driver or hardware: .Pp .Bl -tag -width indent .It Dv V4L2_CAP_VIDEO_CAPTURE support video capturing .It Dv V4L2_CAP_READWRITE supports the .Xr read 2 and/or .Xr write 2 mode .It Dv V4L2_CAP_STREAMING supports .Xr mmap 2 mode .El .Bd -literal 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]; }; .Ed .El .Sh STREAMING INTERFACE .Bl -tag -width indent .It Dv VIDIOC_REQBUFS (struct v4l2_requestbuffers) This command requests that the driver reserve space for .Va count samples. .Va type must be set to .Dv V4L2_BUF_TYPE_VIDEO_CAPTURE and .Va memory to .Dv V4L2_MEMORY_MMAP . The returned .Va count represents the actual number of samples reserved which may be more or fewer than requested. .Bd -literal struct v4l2_requestbuffers { uint32_t count; enum v4l2_buf_type type; enum v4l2_memory memory; uint32_t reserved[2]; }; .Ed .It Dv VIDIOC_QUERYBUF (struct v4l2_buffer) This command should be called for each buffer in .Va count above. The fields .Va index , .Va type , and .Va memory must be set to a valid index from 0 to .Va count-1 , and the same type and memory as used in .Dv VIDIOC_QUERYBUF . The driver returns .Va m.offset and .Va length . .Bd -literal 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; }; .Ed .It Xr mmap 2 Each buffer must be mapped with a call to .Xr mmap 2 , passing the .Va length and .Va m.offset values obtained above. The prot .Dv PROT_READ|PROT_WRITE and flags .Dv MAP_SHARED are recommended. .It Dv 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: .Va index , set to a valid buffer index from 0 to .Va count \- 1; .Va type , set to the same type used above; and .Va memory , set to the same memory used above. Each buffer should be queued with this command. Order is not important. .It Dv VIDIOC_STREAMON (int) This command starts streaming. Queued buffers will be filled with data. .Xr select 2 will indicate that a buffer is done and available for reading. .It Dv 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 .Dv O_NONBLOCK was specified to .Xr open 2 , in which case it returns .Er EAGAIN . .Xr select 2 , or .Xr poll 2 prior to initiating any other mode will begin streaming of video for reading with .Xr read 2 . In this streaming mode .Xr select 2 or .Xr poll 2 indicate the availability of a video frame. Calls to .Xr 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. .El .Sh FILES .Bl -tag -width /dev/video -compact .It Pa /dev/video .El .Sh SEE ALSO .Xr auvitek 4 , .Xr pseye 4 , .Xr uvideo 4 , .Xr video 9 .Pp .Lk http://v4l2spec.bytesex.org/ "V4L2 API Specification" .Sh HISTORY The .Nm device driver first appeared in .Nx 5.0 . .Sh AUTHORS .An Patrick Mahoney Aq Mt pat@polycrystal.org .Sh BUGS Does not support the complete V4L2 API. Only supports the capture interface. Does not support writing, overlay, VBI, tuner, audio, radio, or asyncio.