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• Stream to youtube from xvfb using ffmpeg and x11grab

  13 décembre 2017, par Ivan Sergeev

  I want to make stream from virtual display to youtube via ffmpeg.
  I’m using this code :

  #! /bin/bash
  
  
  
  BITRATE="2500k"                                    
  
  FPS="30"                                       
  
  
  
  YOUTUBE_URL="rtmp://a.rtmp.youtube.com/live2"  
  
  YOUTUBE_KEY="..."                                     
  
  
  
  SOURCE="./test.mp4"
  
  
  
  export DISPLAY=44
  
  sudo xvfb-run -a -n 44 -l -s "-screen 0, 1280x720x24" google-chrome -start-maximized https://upload.wikimedia.org/wikipedia/commons/2/2c/Rotating_earth_%28large%29.gif --no-sandbox >/dev/null &
  
  
  
  ffmpeg -threads 0 -y -v verbose -re \
  
   -f x11grab -video_size 1280x720 -i :44 \
  
   -vcodec libx264 -pix_fmt yuv420p -preset ultrafast -r $FPS -g $(($FPS * 2)) -b:v $BITRATE -bufsize 512k \
  
   -acodec libmp3lame -ar 44100 -threads 0 -crf 25 -b:a 712000 -bufsize 512k \
  
   -f flv "$YOUTUBE_URL/$YOUTUBE_KEY"

  And I don’t receive any errors, but youtube cannot start stream(

  In my log :

  Stream mapping:
  
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  frame=    4 fps=0.0 q=17.0 size=      72kB time=00:00:00.50 bitrate=1186.9kbits/s
  
  frame=    6 fps=5.9 q=17.0 size=     106kB time=00:00:00.93 bitrate= 931.2kbits
  
  frame=    8 fps=5.3 q=17.0 size=     141kB time=00:00:01.36 bitrate= 846.4kbits/s
  
  frame=   11 fps=5.4 q=16.0 size=     188kB time=00:00:02.00 bitrate= 771.9kbits/s
  
  frame=   13 fps=5.2 q=15.0 size=     217kB time=00:00:02.43 bitrate= 730.5kbits/s
  
  frame=   15 fps=5.0 q=14.0 size=     241kB time=00:00:02.86 bitrate= 687.2kbits/s
  
  frame=   18 fps=5.1 q=14.0 size=     270kB time=00:00:03.53 bitrate= 625.2kbits/s
  
  frame=   20 fps=4.9 q=15.0 size=     294kB time=00:00:03.96 bitrate= 608.3kbits/s

  etc.

  However, if I do stream from file, but not x11grab stream is starting normal.

  What I’m doing wrong ?
  Any ideas, guys, please)

• simple way te to compute rgb buffer from I420 frame ffmpeg

  9 mars 2023, par hacenesh

  I'm trying to compute directly rgb buffer from avframe. Something is going wrong since the obtained image is wrong. Extracting grey image from AVFrame->data[0] is working fine. However I'm not able to extract colored image

  


  inline void YCrCb_to_RGB8(int Y, int Cr, int Cb, int& R, int& G, int& B){

   R = (int)(Y + 1.402 *(Cr - 128));
   G = (int)(Y - 0.344136*(Cb-128) -0.71414*(Cr-128));
   B = (int)(Y + 1.772 *(Cb-128));

   if (R < 0) R = 0; else if (R > 255) R = 255;
   if (G < 0) G = 0; else if (G > 255) G = 255;
   if (B < 0) B = 0; else if (B > 255) B = 255;
}

int getRGB8buffer(AVFrame* pFrame, byte* buffer){

   const int width = pFrame->width, height = pFrame->height;
   int Y, Cr, Cb;
   int R, G, B;

   int pixel = 0;
   for (int y = 0; y < height; y++)
   {
    for (int x = 0; x < width; x++)
    {

        Y = pFrame->data[0][x + y * width];
        Cr = pFrame->data[1][x / 2 + ((int)(y / 2)) * pFrame->linesize[1]];
        Cb = pFrame->data[2][x / 2 + ((int)(y / 2)) * pFrame->linesize[2]];

        YCrCb_to_RGB8(Y, Cr, Cb, R, G, B);
        buffer[pixel * 3 + 0] = R;
        buffer[pixel * 3 + 1] = G;
        buffer[pixel * 3 + 2] = B;
        pixel++;
    }
   }
   return 0;
}


  


  When I save the obtained image as ppm using

  


  int save_RGB_frame(unsigned char* buf, int wrap, int xsize,int ysize, const char* filename){

   FILE* f;
   int i;
   f = fopen(filename, "w");
   // portable ppm format -> https://en.wikipedia.org/wiki/Netpbm#PPM_example
   fprintf(f, "P6\n%d %d\n%d\n", xsize, ysize, 255);

   // writing line by line
   for (i = 0; i < ysize; i++)
      fwrite(buf + i * wrap, 1, xsize*3, f);
   fclose(f);

   return 0;
 }


  


  The resulting image is wrong
link the the resulting image https://github.com/hacenesh/ffmpeg_question/blob/main/img_2028144.ppm

  


• Get Total number of frames and FPS faster than with OpenCV library in C++

  20 juillet 2018, par daniels_pa

  I need to check which video can be analyzed and which cannot given the total number of frames in a video and the fps of the video. I created a c++ program to do the checking. Analyzing each video is not an option since analyzing is time consuming.

  I used the OpenCV library for starters :

      cv::VideoCapture vid_to_analyze;
  
      vid_to_analyze.open( me_vid.vid_path.string() );
  
      me_vid.total_frames= static_cast<int>(vid_to_analyze.get(CV_CAP_PROP_FRAME_COUNT));
  
      me_vid.fps=vid_to_analyze.get(CV_CAP_PROP_FPS);
  
  
  
      if (!vid_to_analyze.isOpened())
  
      {
  
          std::cout &lt;&lt; "Skipping vid: "&lt;&lt; me_vid.vid_path.string()&lt;&lt;", couldn't open it" &lt;&lt; std::endl;
  
      }
  
      if (me_vid.fps != me_vid.fps || me_vid.fps &lt;= 0)
  
      {
  
          std::cout &lt;&lt; "For video " &lt;&lt; me_vid.vid_path.string() &lt;&lt; std::endl;
  
          std::cout &lt;&lt; "FPS of the video file cannot be determined, assuming 30"&lt;&lt; std::endl;
  
          me_vid.fps = 30;
  
      }
  
  
  
      vid_to_analyze.release();
  
  </int>

  However when debugging it becomes painfully slow (the program is faster running without the debugger attached but still very slow given the number of videos it needs to cover). I think that has something to do with 4 threads being created and deleted each time a video is opened (released).

  How to get total number of frames and fps in a faster manner ( without actually creating 4 threads !!) if i am not interested in actually grabbing frames from the video just the number of frames and fps.

  Is there a way to use ffmpeg library from c++, would that be faster and where to start ?

  EDIT : Valgrind seems to agree since (Ir=)91.66% of time spend in the vid_to_analyze.open phase