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.\" $OpenBSD: video.4,v 1.4 2008/06/28 19:35:42 mglocker Exp $
.\"
.\" Copyright (c) 2008 Marcus Glocker <mglocker@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 28 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 autoamtically 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 .
|
