VIDEO(4) OpenBSD Programmer's Manual VIDEO(4)NAMEvideo - device-independent video driver layer
SYNOPSIS
video* at uvideo?
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/videoio.h>
DESCRIPTION
The video driver provides support for various video devices. It provides
a uniform programming interface layer above different underlying video
hardware drivers. The video 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 video
driver.
IOCTLS
The following ioctl(2) commands are supported:
VIDIOC_QUERYCAP (struct v4l2_capability *)
Query device capabilities.
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];
};
VIDIOC_ENUM_FMT (struct v4l2_fmtdesc *)
Enumerate image formats.
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];
};
VIDIOC_S_FMT (struct v4l2_format *)
Set the data format.
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;
};
VIDIOC_G_FMT (struct v4l2_format *)
Get the data format.
Same structure as for VIDIOC_S_FMT.
VIDIOC_ENUMINPUT (struct v4l2_input *)
Enumerate video inputs.
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];
};
VIDIOC_S_INPUT (int *)
Select the current video input.
VIDIOC_REQBUFS (struct v4l2_requestbuffers *)
Initiate memory mapping or user pointer I/O.
struct v4l2_requestbuffers {
u_int32_t count;
enum v4l2_buf_type type;
enum v4l2_memory memory;
u_int32_t reserved[2];
};
VIDIOC_QUERYBUF (struct v4l2_buffer *)
Query the status of a buffer.
struct v4l2_buffer {
u_int32_t index;
enum v4l2_buf_type type;
u_int32_t bytesused;
u_int32_t flags;
enum v4l2_field field;
struct timeval timestamp;
struct v4l2_timecode timecode;
u_int32_t sequence;
enum v4l2_memory memory;
union {
u_int32_t offset;
unsigned long userptr;
} m;
u_int32_t length;
u_int32_t input;
u_int32_t reserved;
};
VIDIOC_QBUF (struct v4l2_buffer *)
Add a buffer to the queue.
Same structure as for VIDIOC_QUERYBUF.
VIDIOC_DQBUF (struct v4l2_buffer *)
Remove a buffer from the queue.
Same structure as for VIDIOC_QUERYBUF.
VIDIOC_STREAMON (int *)
Start video stream.
VIDIOC_STREAMOFF (int *)
Stop video stream.
VIDIOC_TRY_FMT (struct v4l2_format *)
Try a data format.
Same structure as for VIDIOC_S_FMT.
VIDIOC_QUERYCTRL (struct v4l2_queryctrl *)
Enumerate control items.
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];
};
Command independent enumerations are:
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,
};
Command independent structures are:
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];
};
Command independent typedefs are:
typedef u_int64_t v4l2_std_id;
READ
Video data can be accessed via the read(2) system call. The main
iteration for userland applications occurs as follow:
1. Open /dev/video* via the open(2) system call.
2. Read video data from the device via the 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.
3. Process video data and start over again with step 2.
4. When finished stop the video stream via the close(2) system
call.
The select(2) and poll(2) system calls are supported for this access
type. They will signal when a frame is ready for reading without
blocking.
MMAP
Video data can be accessed via the mmap(2) system call. The main
iteration for userland applications occurs as follow:
1. Open /dev/video* via the open(2) system call.
2. Request desired number of buffers via the VIDIOC_REQBUFS ioctl
command. The maximum number of available buffers is normally
limited by the hardware driver.
3. Get the length and offset for the previously requested buffers
via the VIDIOC_QUERYBUF ioctl command and map the buffers via
the mmap(2) system call.
4. Initially queue the buffers via the VIDIOC_QBUF ioctl command.
5. Start the video stream via the VIDIOC_STREAMON ioctl command.
6. 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).
7. Requeue the buffer via the VIDIOC_QBUF ioctl command.
8. Process video data and start over again with step 6.
9. When finished stop the video stream via the VIDIOC_STREAMOFF
ioctl command.
The select(2) and poll(2) system calls are supported for this access
type. They will signal when at least one frame is ready for dequeuing,
allowing to call the VIDIOC_DQBUF ioctl command without blocking.
FILES
/dev/video
SEE ALSOioctl(2), uvideo(4)HISTORY
The video driver first appeared in OpenBSD 4.4.
OpenBSD 4.9 July 22, 2010 OpenBSD 4.9
