OpenBSD-4.6/share/man/man4/video.4

.\" $OpenBSD: video.4,v 1.5 2008/09/13 05:37:12 jmc Exp $
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.\" Copyright (c) 2008 Marcus Glocker <mglocker@openbsd.org>
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.Dd $Mdocdate: September 13 2008 $
.Dt VIDEO 4
.Os
.Sh NAME
.Nm video
.Nd device-independent video driver layer
.Sh SYNOPSIS
.Cd "video* at uvideo?"
.Pp
.Fd #include <sys/types.h>
.Fd #include <sys/ioctl.h>
.Fd #include <sys/videoio.h>
.Sh DESCRIPTION
The
.Nm
driver provides support for various video devices.
It provides a uniform programming interface layer
above different underlying video hardware drivers.
The
.Nm
driver uses the V4L2 (Video for Linux Two) API which is widely used by video
applications.
Therefore this document mainly describes the V4L2 API parts
which are supported by the
.Nm
driver.
.Sh IOCTLS
The following
.Xr ioctl 2
commands are supported:
.Bl -tag -width Ds
.It VIDIOC_QUERYCAP (struct v4l2_capability *)
Query device capabilities.
.Bd -literal
struct v4l2_capability {
	u_int8_t	driver[16];
	u_int8_t	card[32];
	u_int8_t	bus_info[32];
	u_int32_t	version;
	u_int32_t	capabilities;
	u_int32_t	reserved[4];
};
.Ed
.It VIDIOC_ENUM_FMT (struct v4l2_fmtdesc *)
Enumerate image formats.
.Bd -literal
struct v4l2_fmtdesc {
	u_int32_t		index;
	enum v4l2_buf_type	flags;
	u_int8_t		description[32];
	u_int32_t		pixelformat;
	u_int32_t		reserved[4];
};
.Ed
.It VIDIOC_S_FMT (struct v4l2_format *)
Set the data format.
.Bd -literal
struct v4l2_format {
	enum v4l2_buf_type	type;
	union {
		struct v4l2_pix_format		pix;
		struct v4l2_window		win;
		struct v4l2_vbi_format		vbi;
		struct v4l2_sliced_vbi_format	sliced;
		u_int8_t			raw_data[200];
        } fmt;
};
.Ed
.It VIDIOC_G_FMT (struct v4l2_format *)
Get the data format.
.Pp
Same structure as for VIDIOC_S_FMT.
.It VIDIOC_ENUMINPUT (struct v4l2_input *)
Enumerate video inputs.
.Bd -literal
struct v4l2_input {
	u_int32_t	index;
	u_int8_t	name[32];
	u_int32_t	type;
	u_int32_t	audioset;
	u_int32_t	tuner;
	v4l2_std_id	std;
	u_int32_t	status;
	u_int32_t	reserved[32];
};
.Ed
.It VIDIOC_S_INPUT (int)
Select the current video input.
.It VIDIOC_REQBUFS (struct v4l2_requestbuffers *)
Initiate memory mapping or user pointer I/O.
.Bd -literal
struct v4l2_requestbuffers {
	u_int32_t		count;
	enum v4l2_buf_type	type;
	enum v4l2_memory	memory;
	u_int32_t		reserved[2];
};
.Ed
.It VIDIOC_QUERYBUF (struct v4l2_buffer *)
Query the status of a buffer.
.Pp
Same structure as for VIDIOC_REQBUFS.
.It VIDIOC_QBUF (struct v4l2_buffer *)
Add a buffer to the queue.
.Pp
Same structure as for VIDIOC_REQBUFS.
.It VIDIOC_DQBUF (struct v4l2_buffer *)
Remove a buffer from the queue.
.Pp
Same structure as for VIDIOC_REQBUFS.
.It VIDIOC_STREAMON (int)
Start video stream.
.It Dv VIDIOC_STREAMOFF (int)
Stop video stream.
.It VIDIOC_TRY_FMT (struct v4l2_format *)
Try a data format.
.Pp
Same structure as for VIDIOC_S_FMT.
.It VIDIOC_QUERYCTRL (struct v4l2_queryctrl *)
Enumerate control items.
.Bd -literal
struct v4l2_queryctrl {
	u_int32_t		id;
	enum v4l2_ctrl_type	type;
	u_int8_t		name[32];
	int32_t			minimum;
	int32_t			maximum;
	int32_t			step;
	int32_t			default_value;
	u_int32_t		flags;
	u_int32_t		reserved[2];
};
.Ed
.El
.Pp
Command independent enumerations are:
.Bd -literal
enum v4l2_buf_type {
	V4L2_BUF_TYPE_VIDEO_CAPTURE = 1,
	V4L2_BUF_TYPE_VIDEO_OUTPUT = 2,
	V4L2_BUF_TYPE_VIDEO_OVERLAY = 3,
	V4L2_BUF_TYPE_VBI_CAPTURE = 4,
	V4L2_BUF_TYPE_VBI_OUTPUT = 5,
	V4L2_BUF_TYPE_SLICED_VBI_CAPTURE = 6,
	V4L2_BUF_TYPE_SLICED_VBI_OUTPUT = 7,
	V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY = 8,
	V4L2_BUF_TYPE_PRIVATE = 0x80,
};

enum v4l2_memory {
	V4L2_MEMORY_MMAP = 1,
	V4L2_MEMORY_USERPTR = 2,
	V4L2_MEMORY_OVERLAY = 3,
};

enum v4l2_ctrl_type {
	V4L2_CTRL_TYPE_INTEGER = 1,
	V4L2_CTRL_TYPE_BOOLEAN = 2,
	V4L2_CTRL_TYPE_MENU = 3,
	V4L2_CTRL_TYPE_BUTTON = 4,
	V4L2_CTRL_TYPE_INTEGER64 = 5,
	V4L2_CTRL_TYPE_CTRL_CLASS = 6,
};
.Ed
.Pp
Command independent structures are:
.Bd -literal
struct v4l2_pix_format {
	u_int32_t		width;
	u_int32_t		height;
	u_int32_t		pixelformat;
	enum v4l2_field		field;
	u_int32_t		bytesperline;
	u_int32_t		sizeimage;
	enum v4l2_colorspace	colorspace;
	u_int32_t		priv;
};

struct v4l2_window {
	struct v4l2_rect	 w;
	enum v4l2_field		 chromakey;
	struct v4l2_clip	 __user *clips;
	u_int32_t		 clipcount;
	void __user		*bitmap;
	u_int8_t		 global_alpha;
};

struct v4l2_vbi_format {
	u_int32_t		sampling_rate;
	u_int32_t		offset;
	u_int32_t		samples_per_line;
	u_int32_t		sample_format;
	int32_t			start[2];
	u_int32_t		count[2];
	u_int32_t		flags;
	u_int32_t		reserved[2];
};

struct v4l2_sliced_vbi_format {
	u_int16_t	service_set;
	u_int16_t	service_lines[2][24];
	u_int32_t	io_size;
	u_int32_t	reserved[2];
};
.Ed
.Pp
Command independent typedefs are:
.Bd -literal
typedef u_int64_t	v4l2_std_id;
.Ed
.Sh READ
Video data can be accessed via the
.Xr read 2
system call.
The main iteration for userland applications occurs as follow:
.Pp
.Bl -enum -compact -offset indent
.It
Open /dev/video* via the
.Xr open 2
system call.
.It
Read video data from the device via the
.Xr read 2
system call.
The video stream will be started automatically with the first
read, which means there is no need to issue a VIDIOC_STREAMON command.
The read will always return a consistent video frame, if no error occurs.
.It
Process video data and start over again with step 2.
.It
When finished stop the video stream via the
.Xr close 2
system call.
.El
.Sh MMAP
Video data can be accessed via the
.Xr mmap 2
system call.
The main iteration for userland applications occurs as follow:
.Pp
.Bl -enum -compact -offset indent
.It
Open /dev/video* via the
.Xr open 2
system call.
.It
Request desired number of buffers via the VIDIOC_REQBUFS ioctl command.
The maximum number of available buffers is normally limited by the hardware
driver.
.It
Map the buffers via the
.Xr mmap 2
system call.
.It
Initially queue the buffers via the VIDIOC_QBUF ioctl command.
.It
Start the video stream via the VIDIOC_STREAMON ioctl command.
.It
Dequeue one buffer via the VIDIOC_DQBUF ioctl command.
If the queue is empty
the ioctl will block until a buffer gets queued or an error occurs
(e.g. a timeout).
.It
Requeue the buffer via the VIDIOC_QBUF ioctl command.
.It
Process video data and start over again with step 6.
.It
When finished stop the video stream via the VIDIOC_STREAMOFF ioctl command.
.El
.Sh FILES
.Bl -tag -width /dev/video -compact
.It Pa /dev/video
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr uvideo 4
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 4.4 .