convert FFmpeg AVFrame to OpenCV Mat

avframe_to_cvmat.cpp

#include <opencv2/opencv.hpp>

extern "C" 
{
  #include <libswscale/swscale.h>
  #include <libavutil/imgutils.h>
  #include <libavutil/frame.h>
}
// link libswscale in c++
// ref: https://soledadpenades.com/posts/2009/linking-with-ffmpegs-libav/

void convert(struct AVFrame *frame) {
  int w = frame->width;
  int h = frame->height;

  AVFrame *frameBGR = av_frame_alloc(); // opencv use BGR color space
  av_image_alloc(frameBGR->data, frameBGR->linesize, frame->width, frame->height, AV_PIX_FMT_BGR24, 1);

  struct SwsContext *ctx = sws_getContext(
    w, h, (AVPixelFormat)frame->format, 
    w, h, AV_PIX_FMT_BGR24, 
    SWS_FAST_BILINEAR, NULL, NULL, NULL);
  sws_scale(ctx, frame->data, frame->linesize, 0, h, frameBGR->data, frameBGR->linesize);
  
  // mat type should match pix_fmt param of av_image_alloc, 8 x 3 = 24
  cv::Mat mat = cv::Mat(h, w, CV_8UC3, frameBGR->data[0], frameBGR->linesize[0]);

  sws_freeContext(ctx);
  av_freep(&frameBGR->data);
  av_frame_free(&frameBGR);
  
  //do something with mat
}

avframe_to_cvmat.h

#ifndef FTM_H
#define FTM_H

//using in pure C

#ifdef __cplusplus
extern "C" {
#endif

  // forward declarations
  typedef struct AVFrame AVFrame;

  convert(struct AVFrame *frame);

#ifdef __cplusplus
}
#endif

#endif