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Video

The video driver API offers a generic interface to video devices.

Basic Operation

Video Device

A video device is the abstraction of a hardware or software video function, which can produce, process, consume or transform video data. The video API is designed to offer flexible way to create, handle and combine various video devices.

Endpoint

Each video device can have one or more endpoints. Output endpoints configure video output function and generate data. Input endpoints configure video input function and consume data.

Video Buffer

A video buffer provides the transport mechanism for the data. There is no particular requirement on the content. The requirement for the content is defined by the endpoint format. A video buffer can be queued to a device endpoint for filling (input ep) or consuming (output ep) operation, once the operation is achieved, buffer can be dequeued for post-processing, release or reuse.

Controls

A video control is accessed and identified by a CID (control identifier). It represents a video control property. Different devices will have different controls available which can be generic, related to a device class or vendor specific. The set/get control functions provide a generic scalable interface to handle and create controls.

Configuration Options

Related configuration options:

API Reference

group video_interface

Video Interface.

Defines

video_fourcc(a, b, c, d)
VIDEO_PIX_FMT_BGGR8
VIDEO_PIX_FMT_GBRG8
VIDEO_PIX_FMT_GRBG8
VIDEO_PIX_FMT_RGGB8
VIDEO_PIX_FMT_RGB565

Typedefs

typedef video_api_set_format_t

Set video format See video_set_format() for argument descriptions.

typedef video_api_get_format_t

get current video format See video_get_format() for argument descriptions.

typedef video_api_enqueue_t

Enqueue a buffer in the driver’s incoming queue. See video_enqueue() for argument descriptions.

typedef video_api_dequeue_t

Dequeue a buffer from the driver’s outgoing queue. See video_dequeue() for argument descriptions.

typedef video_api_flush_t

Flush endpoint buffers, buffer are moved from incoming queue to outgoing queue. See video_flush() for argument descriptions.

typedef video_api_stream_start_t

Start the capture or output process. See video_stream_start() for argument descriptions.

typedef video_api_stream_stop_t

Stop the capture or output process. See video_stream_stop() for argument descriptions.

typedef video_api_set_ctrl_t

set a video control value. See video_set_ctrl() for argument descriptions.

typedef video_api_get_ctrl_t

get a video control value. See video_get_ctrl() for argument descriptions.

typedef video_api_get_caps_t

Get capabilities of a video endpoint. See video_get_caps() for argument descriptions.

typedef video_api_set_signal_t

Register/Unregister poll signal for buffer events. See video_set_signal() for argument descriptions.

Enums

enum video_endpoint_id

video_endpoint_id enum Identify the video device endpoint.

Values:

VIDEO_EP_NONE
VIDEO_EP_ANY
VIDEO_EP_IN
VIDEO_EP_OUT
enum video_signal_result

video_event enum Identify video event.

Values:

VIDEO_BUF_DONE
VIDEO_BUF_ABORTED
VIDEO_BUF_ERROR

Functions

static int video_set_format(struct device *dev, enum video_endpoint_id ep, struct video_format *fmt)

Set video format.

Configure video device with a specific format.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • fmt: Pointer to a video format struct.

Return Value
  • 0: Is successful.

  • -EINVAL: If parameters are invalid.

  • -ENOTSUP: If format is not supported.

  • -EIO: General input / output error.

static int video_get_format(struct device *dev, enum video_endpoint_id ep, struct video_format *fmt)

Get video format.

Get video device current video format.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • fmt: Pointer to video format struct.

Return Value
  • pointer: to video format

static int video_enqueue(struct device *dev, enum video_endpoint_id ep, struct video_buffer *buf)

Enqueue a video buffer.

Enqueue an empty (capturing) or filled (output) video buffer in the driver’s endpoint incoming queue.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • buf: Pointer to the video buffer.

Return Value
  • 0: Is successful.

  • -EINVAL: If parameters are invalid.

  • -EIO: General input / output error.

static int video_dequeue(struct device *dev, enum video_endpoint_id ep, struct video_buffer **buf, k_timeout_t timeout)

Dequeue a video buffer.

Dequeue a filled (capturing) or displayed (output) buffer from the driver’s enpoint outgoing queue.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • buf: Pointer a video buffer pointer.

  • timeout: Timeout

Return Value
  • 0: Is successful.

  • -EINVAL: If parameters are invalid.

  • -EIO: General input / output error.

static int video_flush(struct device *dev, enum video_endpoint_id ep, bool cancel)

Flush endpoint buffers.

A call to flush finishes when all endpoint buffers have been moved from incoming queue to outgoing queue. Either because canceled or fully processed through the video function.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • cancel: If true, cancel buffer processing instead of waiting for completion.

Return Value
  • 0: Is successful, -ERRNO code otherwise.

static int video_stream_start(struct device *dev)

Start the video device function.

video_stream_start is called to enter ‘streaming’ state (capture, output…). The driver may receive buffers with video_enqueue() before video_stream_start is called. If driver/device needs a minimum number of buffers before being able to start streaming, then driver set the min_vbuf_count to the related endpoint capabilities.

Return Value
  • 0: Is successful.

  • -EIO: General input / output error.

static int video_stream_stop(struct device *dev)

Stop the video device function.

On video_stream_stop, driver must stop any transactions or wait until they finish.

Return Value
  • 0: Is successful.

  • -EIO: General input / output error.

static int video_get_caps(struct device *dev, enum video_endpoint_id ep, struct video_caps *caps)

Get the capabilities of a video endpoint.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • caps: Pointer to the video_caps struct to fill.

Return Value
  • 0: Is successful, -ERRNO code otherwise.

static int video_set_ctrl(struct device *dev, unsigned int cid, void *value)

Set the value of a control.

This set the value of a video control, value type depends on control ID, and must be interpreted accordingly.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • cid: Control ID.

  • value: Pointer to the control value.

Return Value
  • 0: Is successful.

  • -EINVAL: If parameters are invalid.

  • -ENOTSUP: If format is not supported.

  • -EIO: General input / output error.

static int video_get_ctrl(struct device *dev, unsigned int cid, void *value)

Get the current value of a control.

This retrieve the value of a video control, value type depends on control ID, and must be interpreted accordingly.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • cid: Control ID.

  • value: Pointer to the control value.

Return Value
  • 0: Is successful.

  • -EINVAL: If parameters are invalid.

  • -ENOTSUP: If format is not supported.

  • -EIO: General input / output error.

static int video_set_signal(struct device *dev, enum video_endpoint_id ep, struct k_poll_signal *signal)

Register/Unregister k_poll signal for a video endpoint.

Register a poll signal to the endpoint, which will be signaled on frame completion (done, aborted, error). Registering a NULL poll signal unregisters any previously registered signal.

Parameters
  • dev: Pointer to the device structure for the driver instance.

  • ep: Endpoint ID.

  • signal: Pointer to k_poll_signal

Return Value
  • 0: Is successful, -ERRNO code otherwise.

struct video_buffer *video_buffer_alloc(size_t size)

Allocate video buffer.

Parameters
  • size: Size of the video buffer.

Return Value
  • pointer: to allocated video buffer

void video_buffer_release(struct video_buffer *buf)

Release a video buffer.

Parameters
  • buf: Pointer to the video buffer to release.

struct video_format
#include <video.h>

video format structure

Used to configure frame format.

Parameters
  • pixelformat: is the fourcc pixel format value.

  • width: is the frame width in pixels.

  • height: is the frame height in pixels.

  • pitch: is the line stride, the number of bytes that needs to be added to the address in the first pixel of a row in order to go to the address of the first pixel of the next row (>=width).

struct video_format_cap
#include <video.h>

video format capability

Used to describe a video endpoint format capability.

Parameters
  • pixelformat: is a list of supported pixel formats (0 terminated).

  • width_min: is the minimum supported frame width.

  • width_max: is the maximum supported frame width.

  • height_min: is the minimum supported frame width.

  • height_max: is the maximum supported frame width.

  • width_step: is the width step size.

  • height_step: is the height step size.

struct video_caps
#include <video.h>

video capabilities

Used to describe video endpoint capabilities.

Parameters
  • format_caps: is a list of video format capabilities (zero terminated).

  • min_vbuf_count: is the minimal count of video buffers to enqueue before being able to start the stream.

struct video_buffer
#include <video.h>

video buffer structure

Represent a video frame.

Parameters
  • driver_data: is a pointer to driver specific data.

  • buffer: is a pointer to the start of the buffer.

  • size: is the size in bytes of the buffer.

  • bytesused: is the number of bytes occupied by the valid data in the buffer.

  • timestamp: is a time reference in milliseconds at which the last data byte was actually received for input endpoints or to be consumed for output endpoints.

group video_controls

Video controls.

Defines

VIDEO_CTRL_CLASS_GENERIC
VIDEO_CTRL_CLASS_CAMERA
VIDEO_CTRL_CLASS_MPEG
VIDEO_CTRL_CLASS_JPEG
VIDEO_CTRL_CLASS_VENDOR
VIDEO_CID_HFLIP
VIDEO_CID_VFLIP
VIDEO_CID_CAMERA_EXPOSURE
VIDEO_CID_CAMERA_GAIN
VIDEO_CID_CAMERA_ZOOM