narfster / v4l2cxx

v4l2 C++ wrapper

Video4Linux2 C++ simple wrapper

• Intro
• How to use
• Examples
  • Pipe to ffplay
• ffmpeg commands

Intro

A simple C++ header library to capture frames from a usb camera into a callback function for image processing.

How to use

Run a simple hello camera to see how easy. no more v4l2 boilrplate code.

// callback function to pipe out image to stdout 
// later pipe to ffplay to display image
void callback_stdout_pipe(uint8_t *p_data, size_t len) {
    uint8_t outBuff[921600];
    util_v4l2::raw_to_rgb(p_data, 0, outBuff, 921600, 640 * 480, 8);
    fwrite(outBuff, 640*480*3, 1, stdout);
}

int main() {
    // a capture instance 
    // device, resolution, pixel format , and callback function this should be known in advance you can use 
    // v4l2-ctl command to figure that out.
    capture cap("/dev/video0", 640,480,pixel_format ::V4L2CXX_PIX_FMT_YUYV,callback_stdout_pipe);
    // start streaming - a blocking function.
    cap.run();
}

Examples

• TODO ; cmake; See example folder

v4l2 Extension unit

• TODO
• TODO example with LI-USB30-V034M

pipe to ffplay

./libv4l2cxx | ffplay -f rawvideo -i pipe:0 -video_size 640x480 -pixel_format rgb24 -framerate 60

ffmpeg commands

Play video device

ffplay -f v4l2 -i /dev/video0 -video_size 640x480 -pixel_format yuyv422 -framerate 30

ffplay -f v4l2 -i /dev/video0 -video_size 640x480 -pixel_format mjpeg

ffplay -f v4l2 -i /dev/video0 -video_size 1280x720 -pixel_format mjpeg -framerate 30

Pipe libv4l2 to ffplay, tell ffplay to use input (-i pipe:0 = stdin standrd input)

./libv4l2cxx | ffplay -f rawvideo -i pipe:0 -video_size 640x480 -pixel_format rgb24 -framerate 60

List formats for device

v4l2-ctl --list-formats

List exdtended formats including resolution info for device

v4l2-ctl --list-formats-ext

v4l2-ctl -L

List controls for device

v4l2-ctl --all

Change control option to value

v4l2-ctl -c <option>=<value>

v4l2-ctl -d /dev/video1 -c exposure_absolute=100