Linux Kernel Media Documentation

http://linuxtv.org/downloads/v4l-dvb-apis/
Admin
Comprehensive documentation for the Linux Kernel media subsystem, covering V4L2 drivers, digital TV...
Tokens:17,172
Snippets:107
Trust Score:9.8
Update:5 months ago
Show doc for...
Tokens:
Raw
### V4L2 Video Capture Example

Source: http://linuxtv.org/downloads/v4l-dvb-apis

This C code demonstrates a basic video capture setup using the V4L2 API. It is typically found in the kernel source tree.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <linux/videodev2.h>

#define CLEAR(x) memset(&(x), 0, sizeof(x))

struct buffer {
	void *start;
	size_t length;
};

static int xioctl(int fd, unsigned long request, void *arg)
{
	int r;

do {
		r = ioctl(fd, request, arg);
	} while (r == -1 && errno == EINTR);

	return r;
}

int main(int argc, char **argv)
{
	struct v4l2_capability cap;
	struct v4l2_cropcap cropcap;
	struct v4l2_crop crop;
	struct v4l2_format fmt;
	struct v4l2_buffer buf;
	struct v4l2_requestbuffers req;
	enum v4l2_buf_type type;
	struct buffer *buffers;
	unsigned int n_buffers;
	int fd;

	fd = open("/dev/video0", O_RDWR | O_NONBLOCK, 0);
	if (fd == -1) {
		perror("Failed to open video device");
		return errno;
	}

	/* Check device capabilities */
	if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
		if (EINVAL == errno)
			fprintf(stderr, "%s is not a V4L2 device\n", argv[0]);
		else
			perror("VIDIOC_QUERYCAP");

		return errno;
	}

	if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
	{
		fprintf(stderr, "The device does not handle real time video capture.\n");
		return errno;
	}

	/* Select video input, if present */
	if (cap.capabilities & V4L2_CAP_INPUT) {
		int i, selected_input = 0;

		for (i = 0; ; i++) {
			struct v4l2_input input;

			input.index = i;
			if (-1 == xioctl(fd, VIDIOC_ENUMINPUT, &input)) {
				break;
			}

			if (input.type == V4L2_INPUT_TYPE_CAMERA) {
				selected_input = i;
				break;
			}
		}
		
		struct v4l2_control ctrl;
		ctrl.id = V4L2_CID_INPUT_PRIORITY;
		if (0 == xioctl(fd, VIDIOC_G_CTRL, &ctrl)) {
			selected_input = ctrl.value;
		}

		CLEAR(input);
		input.index = selected_input;
		if (-1 == xioctl(fd, VIDIOC_S_INPUT, &input)) {
			perror("VIDIOC_S_INPUT");
		}
	}

	/* IMPORTANT: In this example we find that the device can not do */
	/* anything useful, so we simply exit. Later examples will     */
	/* show how to do more useful things.                        */

	CLEAR(cropcap);
	cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
		CLEAR(crop);
		crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		crop.left = cropcap.defrect.left;
		crop.top = cropcap.defrect.top;
		crop.width = cropcap.defrect.width;
		crop.height = cropcap.defrect.height;

		/* Crucial: only set crop if the device actually supports it */
		if (xioctl(fd, VIDIOC_S_CROP, &crop) == -1) {
			/* Errors ignored */
		}
	}

	/* Initialize video capture format */
	CLEAR(fmt);
	fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	fmt.fmt.pix.width = 640; /* Desired capture width */
	fmt.fmt.pix.height = 480; /* Desired capture height */
	fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; /* Pixel format */
	fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; /* Field order */

	/* Check if the format is supported, and adjust if necessary */
	if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) {
		perror("VIDIOC_S_FMT");
		return errno;
	}

	/* Buggy driver paranoia. Check if the framerate is valid */
	{
		struct v4l2_streamparm s;
		CLEAR(s);
		s.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		s.parm.capture.timeperframe.numerator = 1;
		s.parm.capture.timeperframe.denominator = 30;
		if (-1 == xioctl(fd, VIDIOC_S_PARM, &s)) {
			perror("VIDIOC_S_PARM");
			return errno;
		}
	}

	/* Allocate video memory */
	CLEAR(req);
	req.count = 2;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_MMAP;

	if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
		perror("VIDIOC_REQBUFS");
		return errno;
	}

	/* Map the buffers */
	buffers = calloc(1, sizeof(*buffers));
	if (!buffers) {
		fprintf(stderr, "Out of memory\n");
		return ENOMEM;
	}

	n_buffers = req.count;
	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		CLEAR(buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;

		if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf)) {
			perror("VIDIOC_QUERYBUF");
			return errno;
		}

		buffers[n_buffers].length = buf.length;
		buffers[n_buffers].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);

		if (MAP_FAILED == buffers[n_buffers].start) {
			perror("mmap");
			return errno;
		}
	}

	/* Setup data location */
	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		CLEAR(buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;

		/* Queue the buffers */
		if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
			perror("VIDIOC_QBUF");
			return errno;
		}
	}

	/* Start capturing */
	if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)) {
		perror("VIDIOC_STREAMON");
		return errno;
	}

	/* Capture one frame */
	do {
		fd_set fds;
		timeval tv;
		
		FD_ZERO(&fds);
		FD_SET(fd, &fds);
		tv.tv_sec = 2;
		tv.tv_usec = 0;

		int r = select(fd + 1, &fds, NULL, NULL, &tv);

		if (-1 == r) {
			if (EINTR == errno)
				continue;
			perror("select");
			return errno;
		}

		if (0 == r) {
			fprintf(stderr, "Timeout waiting for data\n");
			return 1;
		}

		CLEAR(buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;

		/* Dequeue buffer */
		if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
			perror("VIDIOC_DQBUF");
			return errno;
		}

		/* Process the buffer (e.g., save to file) */
		printf("Captured frame with length: %d\n", buf.bytesused);

		/* Re-queue the buffer */
		if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
			perror("VIDIOC_QBUF");
			return errno;
		}

		break;
	} while (1);

	/* Stop capturing */
	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type)) {
		perror("VIDIOC_STREAMOFF");
		return errno;
	}

	/* Unmap and free buffers */
	for (n_buffers = 0; n_buffers < req.count; ++n_buffers)
		munmap(buffers[n_buffers].start, buffers[n_buffers].length);
	free(buffers);

	close(fd);
	return 0;
}

```

--------------------------------

### ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets the current audio output parameters.

```APIDOC
## ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT

### Description
These ioctls are used to get (`G_AUDOUT`) or set (`S_AUDOUT`) the current audio output parameters, such as the audio standard and channel.

### Method
```
VIDIOC_G_AUDOUT
VIDIOC_S_AUDOUT
```

### Parameters
#### Request Structure (struct v4l2_audout)
- **index** (int) - The index of the audio output device.
- **name** (char[32]) - The name of the audio output device.
- **capability** (int) - Capabilities of the audio output device.
```

--------------------------------

### V4L2 Video Grabber Example

Source: http://linuxtv.org/downloads/v4l-dvb-apis

This C code demonstrates how to grab video frames using the libv4l2 library. It provides a higher-level interface compared to direct ioctl calls.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <linux/videodev2.h>
#include <libv4l2.h>

#define CLEAR(x) memset(&(x), 0, sizeof(x))

struct buffer {
	void *start;
	size_t length;
};

static int xioctl(int fd, unsigned long request, void *arg)
{
	int r;

	do {
		r = v4l2_ioctl(fd, request, arg);
	} while (r == -1 && errno == EINTR);

	return r;
}

int main(int argc, char **argv)
{
	struct v4l2_capability cap;
	struct v4l2_cropcap cropcap;
	struct v4l2_crop crop;
	struct v4l2_format fmt;
	struct v4l2_buffer buf;
	struct v4l2_requestbuffers req;
	enum v4l2_buf_type type;
	struct buffer *buffers;
	unsigned int n_buffers;
	int fd;

	fd = open("/dev/video0", O_RDWR | O_NONBLOCK, 0);
	if (fd == -1) {
		perror("Failed to open video device");
		return errno;
	}

	/* Check device capabilities */
	if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
		if (EINVAL == errno)
			fprintf(stderr, "%s is not a V4L2 device\n", argv[0]);
		else
			perror("VIDIOC_QUERYCAP");

		return errno;
	}

	if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE))
	{
		fprintf(stderr, "The device does not handle real time video capture.\n");
		return errno;
	}

	/* Select video input, if present */
	if (cap.capabilities & V4L2_CAP_INPUT) {
		int i, selected_input = 0;

		for (i = 0; ; i++) {
			struct v4l2_input input;

			input.index = i;
			if (-1 == xioctl(fd, VIDIOC_ENUMINPUT, &input)) {
				break;
			}

			if (input.type == V4L2_INPUT_TYPE_CAMERA) {
				selected_input = i;
				break;
			}
		}
		
		struct v4l2_control ctrl;
		ctrl.id = V4L2_CID_INPUT_PRIORITY;
		if (0 == xioctl(fd, VIDIOC_G_CTRL, &ctrl)) {
			selected_input = ctrl.value;
		}

		CLEAR(input);
		input.index = selected_input;
		if (-1 == xioctl(fd, VIDIOC_S_INPUT, &input)) {
			perror("VIDIOC_S_INPUT");
		}
	}

	/* IMPORTANT: In this example we find that the device can not do */
	/* anything useful, so we simply exit. Later examples will     */
	/* show how to do more useful things.                        */

	CLEAR(cropcap);
	cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
		CLEAR(crop);
		crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		crop.left = cropcap.defrect.left;
		crop.top = cropcap.defrect.top;
		crop.width = cropcap.defrect.width;
		crop.height = cropcap.defrect.height;

		/* Crucial: only set crop if the device actually supports it */
		if (xioctl(fd, VIDIOC_S_CROP, &crop) == -1) {
			/* Errors ignored */
		}
	}

	/* Initialize video capture format */
	CLEAR(fmt);
	fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	fmt.fmt.pix.width = 640; /* Desired capture width */
	fmt.fmt.pix.height = 480; /* Desired capture height */
	fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; /* Pixel format */
	fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; /* Field order */

	/* Check if the format is supported, and adjust if necessary */
	if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) {
		perror("VIDIOC_S_FMT");
		return errno;
	}

	/* Buggy driver paranoia. Check if the framerate is valid */
	{
		struct v4l2_streamparm s;
		CLEAR(s);
		s.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		s.parm.capture.timeperframe.numerator = 1;
		s.parm.capture.timeperframe.denominator = 30;
		if (-1 == xioctl(fd, VIDIOC_S_PARM, &s)) {
			perror("VIDIOC_S_PARM");
			return errno;
		}
	}

	/* Allocate video memory */
	CLEAR(req);
	req.count = 2;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_MMAP;

	if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
		perror("VIDIOC_REQBUFS");
		return errno;
	}

	/* Map the buffers */
	buffers = calloc(1, sizeof(*buffers));
	if (!buffers) {
		fprintf(stderr, "Out of memory\n");
		return ENOMEM;
	}

	n_buffers = req.count;
	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		CLEAR(buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;

		if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf)) {
			perror("VIDIOC_QUERYBUF");
			return errno;
		}

		buffers[n_buffers].length = buf.length;
		buffers[n_buffers].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);

		if (MAP_FAILED == buffers[n_buffers].start) {
			perror("mmap");
			return errno;
		}
	}

	/* Setup data location */
	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		CLEAR(buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;

		/* Queue the buffers */
		if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
			perror("VIDIOC_QBUF");
			return errno;
		}
	}

	/* Start capturing */
	if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)) {
		perror("VIDIOC_STREAMON");
		return errno;
	}

	/* Capture one frame */
	do {
		fd_set fds;
		timeval tv;
		
		FD_ZERO(&fds);
		FD_SET(fd, &fds);
		tv.tv_sec = 2;
		tv.tv_usec = 0;

		int r = select(fd + 1, &fds, NULL, NULL, &tv);

		if (-1 == r) {
			if (EINTR == errno)
				continue;
			perror("select");
			return errno;
		}

		if (0 == r) {
			fprintf(stderr, "Timeout waiting for data\n");
			return 1;
		}

		CLEAR(buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;

		/* Dequeue buffer */
		if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
			perror("VIDIOC_DQBUF");
			return errno;
		}

		/* Process the buffer (e.g., save to file) */
		printf("Captured frame with length: %d\n", buf.bytesused);

		/* Re-queue the buffer */
		if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
			perror("VIDIOC_QBUF");
			return errno;
		}

		break;
	} while (1);

	/* Stop capturing */
	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type)) {
		perror("VIDIOC_STREAMOFF");
		return errno;
	}

	/* Unmap and free buffers */
	for (n_buffers = 0; n_buffers < req.count; ++n_buffers)
		munmap(buffers[n_buffers].start, buffers[n_buffers].length);
	free(buffers);

	close(fd);
	return 0;
}

```

--------------------------------

### ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets the current audio input or output parameters.

```APIDOC
## ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO

### Description
These ioctls are used to get (`G_AUDIO`) or set (`S_AUDIO`) the current audio input or output parameters, such as the audio standard and channel.

### Method
```
VIDIOC_G_AUDIO
VIDIOC_S_AUDIO
```

### Parameters
#### Request Structure (struct v4l2_audio)
- **index** (int) - The index of the audio device.
- **type** (int) - The type of audio device (input or output).
- **capability** (int) - Capabilities of the audio device.
- **fmt** (struct v4l2_audiofmt) - Audio format.
```

--------------------------------

### ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets the value of a control on the video device.

```APIDOC
## ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL

### Description
These ioctls are used to get (`G_CTRL`) or set (`S_CTRL`) the value of a specific control on the video device. Controls can include brightness, contrast, saturation, etc.

### Method
```
VIDIOC_G_CTRL
VIDIOC_S_CTRL
```

### Parameters
#### Request Structure (struct v4l2_control)
- **id** (int) - The identifier of the control.
- **value** (int) - The value of the control (for S_CTRL).
```

--------------------------------

### ioctl VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets the Digital Video (DV) timings for a device.

```APIDOC
## ioctl VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS

### Description
These ioctls are used to get (`G_DV_TIMINGS`) or set (`S_DV_TIMINGS`) the Digital Video (DV) timings for a device. DV timings define the timing parameters for digital video signals.

### Method
```
VIDIOC_G_DV_TIMINGS
VIDIOC_S_DV_TIMINGS
```

### Parameters
#### Request Structure (struct v4l2_dv_timings)
- **type** (int) - The type of the DV timings.
- **bt** (struct v4l2_dv_timings_bt) - BT.656/BT.1120 timings.
- **h_total** (int) - Horizontal total.
- **v_total** (int) - Vertical total.
```

--------------------------------

### ioctl VIDIOC_G_CROP, VIDIOC_S_CROP

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets the current cropping rectangle for video capture or output.

```APIDOC
## ioctl VIDIOC_G_CROP, VIDIOC_S_CROP

### Description
These ioctls are used to get (`G_CROP`) or set (`S_CROP`) the current cropping rectangle for video capture or output. The cropping rectangle defines the portion of the image to be processed.

### Method
```
VIDIOC_G_CROP
VIDIOC_S_CROP
```

### Parameters
#### Request Structure (struct v4l2_crop)
- **type** (int) - The type of the image (e.g., V4L2_BUF_TYPE_VIDEO_CAPTURE).
- **c** (struct v4l2_rect) - The cropping rectangle (left, top, width, height).
```

--------------------------------

### ioctl VIDIOC_ENUMINPUT

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Enumerates video input devices.

```APIDOC
## ioctl VIDIOC_ENUMINPUT

### Description
Enumerates the video input devices available on the V4L2 device. This ioctl allows applications to discover and select different video sources.

### Method
```
VIDIOC_ENUMINPUT
```

### Parameters
#### Request Structure (struct v4l2_input)
- **index** (int) - The index of the input to enumerate.
- **name** (char[32]) - The name of the input.
- **type** (int) - The type of input (e.g., camera, tuner).
- **audioset** (int) - Associated audio inputs.
```

--------------------------------

### ioctl VIDIOC_ENUMAUDIO

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Enumerates audio input or output devices.

```APIDOC
## ioctl VIDIOC_ENUMAUDIO

### Description
Enumerates audio input or output devices associated with the video device. This ioctl can be used to get information about available audio channels.

### Method
```
VIDIOC_ENUMAUDIO
```

### Parameters
#### Request Structure (struct v4l2_audio)
- **index** (int) - The index of the audio device to enumerate.
- **type** (int) - The type of audio device (input or output).
- **name** (char[32]) - The name of the audio device.
- **capability** (int) - Capabilities of the audio device.
```

--------------------------------

### ioctl VIDIOC_ENUMAUDOUT

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Enumerates audio output devices.

```APIDOC
## ioctl VIDIOC_ENUMAUDOUT

### Description
Enumerates audio output devices. This ioctl is used to query information about available audio output devices connected to the system.

### Method
```
VIDIOC_ENUMAUDOUT
```

### Parameters
#### Request Structure (struct v4l2_audout)
- **index** (int) - The index of the audio output device.
- **name** (char[32]) - The name of the audio output device.
- **capability** (int) - Capabilities of the audio output device.
```

--------------------------------

### ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Gets or sets a debug register value on the video chip.

```APIDOC
## ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER

### Description
These ioctls allow reading from and writing to debug registers on the video chip. Use with caution as incorrect values can cause instability.

### Method
```
VIDIOC_DBG_G_REGISTER
VIDIOC_DBG_S_REGISTER
```

### Parameters
#### Request Structure (struct v4l2_dbg_register)
- **entity** (int) - The entity identifier.
- **reg** (unsigned int) - The register address.
- **val** (unsigned int) - The register value (for S_REGISTER).
```

--------------------------------

### ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Sends a command to the video decoder or tries to set a decoder command.

```APIDOC
## ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD

### Description
These ioctls are used to control the video decoder. `VIDIOC_DECODER_CMD` sends a command, while `VIDIOC_TRY_DECODER_CMD` checks if a command is supported.

### Method
```
VIDIOC_DECODER_CMD
VIDIOC_TRY_DECODER_CMD
```

### Parameters
#### Request Structure (struct v4l2_decoder_cmd)
- **type** (int) - The type of decoder command (e.g., V4L2_DECODER_CMD_START, V4L2_DECODER_CMD_STOP).
- **flags** (int) - Flags associated with the command.
- **value** (int) - Additional value for the command.
```

--------------------------------

### V4L2 ioctl Commands

Source: http://linuxtv.org/downloads/v4l-dvb-apis

This section lists various ioctl commands available in the V4L2 API for controlling video capture devices and sub-devices.

```APIDOC
## ioctl VIDIOC_G_EDID, VIDIOC_S_EDID, VIDIOC_SUBDEV_G_EDID, VIDIOC_SUBDEV_S_EDID

### Description
Get or set the Extended Display Identification Data (EDID) for a video device or sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_ENC_INDEX

### Description
Get the encoding index for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS

### Description
Get, set, or try extended controls for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF

### Description
Get or set the frame buffer information for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT

### Description
Get, set, or try the pixel format for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY

### Description
Get or set the frequency for a tuner device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_INPUT, VIDIOC_S_INPUT

### Description
Get or set the current input for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP

### Description
Get or set JPEG compression parameters.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR

### Description
Get or set modulator parameters.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_OUTPUT, VIDIOC_S_OUTPUT

### Description
Get or set the current output for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_PARM, VIDIOC_S_PARM

### Description
Get or set general parameters for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY

### Description
Get or set the priority of a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION

### Description
Get or set the selection rectangle for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_SLICED_VBI_CAP

### Description
Get sliced Vertical Blanking Interval (VBI) capabilities.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_STD, VIDIOC_S_STD, VIDIOC_SUBDEV_G_STD, VIDIOC_SUBDEV_S_STD

### Description
Get or set the standard for a video device or sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER

### Description
Get or set tuner parameters.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_LOG_STATUS

### Description
Log the status of a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_OVERLAY

### Description
Control overlay for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_PREPARE_BUF

### Description
Prepare a buffer for I/O.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_QBUF, VIDIOC_DQBUF

### Description
Queue or dequeue a buffer for video capture or output.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_QUERYBUF

### Description
Query information about a buffer.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_QUERYCAP

### Description
Query the capabilities of a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU

### Description
Query available controls, extended controls, and menu items for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_QUERY_DV_TIMINGS

### Description
Query Digital Video (DV) timings.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD

### Description
Query the standard supported by a video device or sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_REQBUFS

### Description
Request buffers for video capture or output.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_REMOVE_BUFS

### Description
Remove buffers from a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_S_HW_FREQ_SEEK

### Description
Set hardware frequency seek parameters.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF

### Description
Enable or disable streaming for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL

### Description
Enumerate supported frame intervals for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_ENUM_FRAME_SIZE

### Description
Enumerate supported frame sizes for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_ENUM_MBUS_CODE

### Description
Enumerate Media Bus (MBUS) codes supported by a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_CROP, VIDIOC_SUBDEV_S_CROP

### Description
Get or set the cropping rectangle for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT

### Description
Get or set the pixel format for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL

### Description
Get or set the frame interval for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_ROUTING, VIDIOC_SUBDEV_S_ROUTING

### Description
Get or set the routing information for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION

### Description
Get or set the selection rectangle for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_G_CLIENT_CAP, VIDIOC_SUBDEV_S_CLIENT_CAP

### Description
Get or set client capabilities for a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBDEV_QUERYCAP

### Description
Query the capabilities of a sub-device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

```APIDOC
## ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT

### Description
Subscribe to or unsubscribe from events for a video device.

### Method
ioctl

### Endpoint
N/A (ioctl command)

### Parameters
None explicitly defined in this snippet.

### Request Example
N/A

### Response
N/A
```

--------------------------------

### ioctl VIDIOC_ENUMOUTPUT

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Enumerates video output devices.

```APIDOC
## ioctl VIDIOC_ENUMOUTPUT

### Description
Enumerates the video output devices available on the V4L2 device. This ioctl allows applications to discover and select different video sinks.

### Method
```
VIDIOC_ENUMOUTPUT
```

### Parameters
#### Request Structure (struct v4l2_output)
- **index** (int) - The index of the output to enumerate.
- **name** (char[32]) - The name of the output.
- **type** (int) - The type of output (e.g., display, VBI).
```

--------------------------------

### ioctl VIDIOC_CREATE_BUFS

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Creates buffers for streaming I/O operations.

```APIDOC
## ioctl VIDIOC_CREATE_BUFS

### Description
Creates buffers for streaming I/O. This ioctl is used to allocate and manage buffers that will be used for capturing or outputting video data.

### Method
```
VIDIOC_CREATE_BUFS
```

### Parameters
#### Request Structure (struct v4l2_create_buffers)
- **count** (int) - The number of buffers to create.
- **index** (int) - The index of the buffer to create.
- **type** (int) - The type of buffer (e.g., V4L2_BUF_TYPE_VIDEO_CAPTURE).
- **memory** (int) - The memory type (e.g., V4L2_MEMORY_MMAP).
```

--------------------------------

### Digital TV Frontend API

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Documentation for the Digital TV Frontend API, covering querying information, status, properties, and function calls.

```APIDOC
## Digital TV Frontend API

### Description
Provides interfaces for querying frontend information, status, and statistics, and defines property types and function calls for digital TV frontend devices.

### Method
API functions and ioctl commands

### Endpoint
N/A

### Parameters
Details on specific parameters are not provided in this overview.

### Request Example
N/A

### Response
N/A
```

--------------------------------

### ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Sends a command to the video encoder or tries to set an encoder command.

```APIDOC
## ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD

### Description
These ioctls are used to control the video encoder. `VIDIOC_ENCODER_CMD` sends a command, while `VIDIOC_TRY_ENCODER_CMD` checks if a command is supported.

### Method
```
VIDIOC_ENCODER_CMD
VIDIOC_TRY_ENCODER_CMD
```

### Parameters
#### Request Structure (struct v4l2_encoder_cmd)
- **type** (int) - The type of encoder command (e.g., V4L2_ENCODER_CMD_START, V4L2_ENCODER_CMD_STOP).
- **flags** (int) - Flags associated with the command.
- **value** (int) - Additional value for the command.
```

--------------------------------

### Media Controller API - Function Reference

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Reference for core functions within the Media Controller API, used for managing media devices and their topology.

```APIDOC
## media open()

### Description
Opens a media device.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## media close()

### Description
Closes a media device.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## media ioctl()

### Description
Performs control operations on a media device.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_DEVICE_INFO

### Description
Retrieves information about a media device.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_G_TOPOLOGY

### Description
Retrieves the topology of the media device.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_ENUM_ENTITIES

### Description
Enumerates entities within the media device.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_ENUM_LINKS

### Description
Enumerates links within the media device.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_SETUP_LINK

### Description
Sets up a link within the media device.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_IOC_REQUEST_ALLOC

### Description
Allocates a request for media operations.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## request close()

### Description
Closes a media request.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## request ioctl()

### Description
Performs control operations on a media request.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## request poll()

### Description
Polls a media request for events.

### Method
N/A (System Call)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_REQUEST_IOC_QUEUE

### Description
Queues a media request for execution.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.

## ioctl MEDIA_REQUEST_IOC_REINIT

### Description
Reinitializes a media request.

### Method
N/A (ioctl command)

### Endpoint
N/A

### Parameters
None explicitly documented.

### Request Example
None provided.

### Response
None explicitly documented.
```

--------------------------------

### V4L2 close()

Source: http://linuxtv.org/downloads/v4l-dvb-apis

The `close()` function is used to close a video device, releasing associated resources.

```APIDOC
## V4L2 close()

### Description
Closes a video device file descriptor.

### Function Signature
```c
int close(int fd);
```

### Parameters
- **fd** (int) - The file descriptor of the video device to close.
```

--------------------------------

### ioctl VIDIOC_EXPBUF

Source: http://linuxtv.org/downloads/v4l-dvb-apis

Exports a buffer for use with other devices or systems.

```APIDOC
## ioctl VIDIOC_EXPBUF

### Description
Exports a buffer, making it accessible to other devices or systems, typically for DMA operations or inter-process communication.

### Method
```
VIDIOC_EXPBUF
```

### Parameters
#### Request Structure (struct v4l2_exportbuffer)
- **type** (int) - The type of buffer.
- **index** (int) - The index of the buffer to export.
- **fd** (int) - File descriptor for the exported buffer.
```
Tokens:
Raw