CameraFrameSourceOpenCV Class Reference

VideoFrameSource that pulls frames from an OpenCV cv::VideoCapture (e.g. a USB/CSI webcam via V4L2 on Linux/Raspberry Pi, or any other OpenCV-supported backend) - the desktop/Linux counterpart to CameraFrameSource, which targets the ESP32 esp_camera.h driver instead. More...

#include <CameraFrameSourceOpenCV.h>

Inheritance diagram for CameraFrameSourceOpenCV:

Public Member Functions
	CameraFrameSourceOpenCV ()=default
	CameraFrameSourceOpenCV (int device)
bool	begin ()
void	end ()
	Releases the capture device.
const uint8_t *	nextFrame (size_t &len) override
void	setApiPreference (int api)
void	setDevice (const char *device)
void	setJpegQuality (int quality)
void	setVideoInfo (VideoInfo info)
VideoInfo	videoInfo () override
bool	writeTo (Print &out)
	Write the frame to the indicated destination.

Protected Attributes
int	api_preference = cv::CAP_ANY
cv::VideoCapture	cap
int	device_index = 0
const char *	device_string = nullptr
cv::Mat	frame
VideoInfo	info
std::vector< uint8_t >	jpeg_buffer
int	jpeg_quality = 90

Detailed Description

VideoFrameSource that pulls frames from an OpenCV cv::VideoCapture (e.g. a USB/CSI webcam via V4L2 on Linux/Raspberry Pi, or any other OpenCV-supported backend) - the desktop/Linux counterpart to CameraFrameSource, which targets the ESP32 esp_camera.h driver instead.

nextFrame() grabs a picture with cv::VideoCapture::read() and, by default (videoInfo().format == VideoFormat::MJPEG), JPEG-encodes it via cv::imencode() so the result matches CameraFrameSource's own already-encoded-JPEG contract. setVideoInfo() with VideoFormat::RAW instead returns the picture as captured - OpenCV's native 3 bytes/pixel BGR layout, which is what VideoFormat::RAW itself denotes - with no re-encoding, e.g. to feed a VideoEncoder (H264Encoder) directly. As with any VideoFrameSource, the returned pointer is only valid until the next nextFrame() call.

width/height/fps are read back from the capture device in begin() - set them beforehand via setVideoInfo()/the constructor to request specific values from cv::VideoCapture (best effort; not all backends/devices honor every value, so the actually-applied values are what ends up in videoInfo() afterwards).

Author

Phil Schatzmann

Copyright

GPLv3

Constructor & Destructor Documentation

CameraFrameSourceOpenCV() [1/2]

CameraFrameSourceOpenCV ( )

default

CameraFrameSourceOpenCV() [2/2]

CameraFrameSourceOpenCV ( int  device )

inline

Parameters

device

cv::VideoCapture index (e.g. 0 for /dev/video0)

Member Function Documentation

begin()

bool begin ( )

inline

Opens the capture device (cv::VideoCapture::open()), applies any width/height/fps requested via setVideoInfo(), then reads back the values actually in effect.

end()

void end ( )

inline

Releases the capture device.

nextFrame()

const uint8_t * nextFrame ( size_t &  len )

inlineoverridevirtual

Captures a new picture and, unless videoInfo().format is VideoFormat::RAW, JPEG-encodes it - nullptr (len 0) if the capture failed.

Implements VideoFrameSource.

setApiPreference()

void setApiPreference ( int  api )

inline

Selects the capture backend (e.g. cv::CAP_V4L2) - default cv::CAP_ANY lets OpenCV pick. Call before begin().

setDevice()

void setDevice ( const char *  device )

inline

Use a device path/URL/GStreamer pipeline (cv::VideoCapture(const String&)) instead of a numeric index - call before begin().

setJpegQuality()

void setJpegQuality ( int  quality )

inline

JPEG quality (0-100) used to encode frames when videoInfo().format is VideoFormat::MJPEG (the default) - see cv::IMWRITE_JPEG_QUALITY.

setVideoInfo()

void setVideoInfo ( VideoInfo  info )

inline

Requests width/height/fps/format from the capture device - all optional (0/UNKNOWN = leave the device's own default); actually applied on a best-effort basis in begin() via cv::VideoCapture::set(). format only selects nextFrame()'s own output (see class comment), it is not passed to OpenCV. Call before begin().

videoInfo()

VideoInfo videoInfo ( )

inlineoverridevirtual

Provides the width/height/fps/format determined in begin() (or requested explicitly beforehand via setVideoInfo() - see there).

Implements VideoFrameSource.

writeTo()

bool writeTo ( Print &  out )

inlineinherited

Write the frame to the indicated destination.

Member Data Documentation

api_preference

int api_preference = cv::CAP_ANY

protected

cap

cv::VideoCapture cap

protected

device_index

int device_index = 0

protected

device_string

const char* device_string = nullptr

protected

frame

cv::Mat frame

protected

info

VideoInfo info

protected

jpeg_buffer

std::vector<uint8_t> jpeg_buffer

protected

jpeg_quality

int jpeg_quality = 90

protected

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The documentation for this class was generated from the following file:

• src/AudioTools/Video/Camera/CameraFrameSourceOpenCV.h