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• Extracting frame out of video based on time in seconds

  20 avril 2024, par Vicky

  I'm developing a web-based video editing tool where users can pause a video and draw circles or lines on it using canvas. When a user pauses the video, I retrieve the current playback time in seconds using the HTML5 video.currentTime property. I then send this time value along with the shape details to the server. On the server-side, we use FFmpeg to extract the specific paused frame from the video. The issue I'm encountering is a frame mismatch between the one displayed in the browser and the one generated in the backend using FFmpeg.

  


  I've experimented with various approaches for this process.

  


  Extracting frame based on time. Example : in this case time is 3.360 second.

  


  


  ffmpeg -i input.mp4 -ss 00:00:03.360 -frames:v 1 frame.jpg

  


  


  Converting time to frame number using the following logic : Math.round(video.currentTime * fps)

  


  


  ffmpeg -i input.mp4 -vf "select=eq(n,101)" -vsync vfr frame.jpg

  


  


  


  ffmpeg -i input .mp4 -vf "select='lt(t,3.360)lt(3.360-t,1/31.019)',setpts=N/(31.019TB)" -vsync 0 frame.jpg

  


  


  The challenge I'm facing is that sometimes the frame I see in the browser at the pause time doesn't match the one generated in the backend using FFmpeg. How can I solve this problem ? If it's an issue with currentTime, are there any other approaches I can try ?

  


• FFMPEG Incompatible sprop-parameter-sets with libstagefright on Android 4.0 for H264

  7 août 2012, par user1582384

  I am having an issue with the RTSP SDP generated by FFMPEG in Android.
  I have the FFMPEG 0.11.1 compiled with NDK and running on Android. I use the FFSERVER to stream an mp4 file locally to the MediaPlayer.

  Here is the generated SDP description :

  08-07 14:04:04.034 : V/rtsp_server(20161) : o=- 0 0 IN IP4 127.0.0.1

  08-07 14:04:04.034 : V/rtsp_server(20161) : s=No Title

  08-07 14:04:04.034 : V/rtsp_server(20161) : c=IN IP4 0.0.0.0

  08-07 14:04:04.034 : V/rtsp_server(20161) : t=0 0

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=tool:libavformat 54.6.100

  08-07 14:04:04.034 : V/rtsp_server(20161) : m=video 0 RTP/AVP 96

  08-07 14:04:04.034 : V/rtsp_server(20161) : b=AS:312

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=x-dimensions:512,384

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=rtpmap:96 H264/90000

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=fmtp:96
  packetization-mode=0 ;profile-level-id=640015 ;sprop-parameter-sets=J2QAH62ECSZuIzSQgSTNxGaSECSZuIzSQgSTNxGaSECSZuIzSQgSTNxGaSEFWuvX1+T+vyfXrrVQgq116+vyf1+T69daq0BAGMg=,KO48sA==

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=control:streamid=0

  08-07 14:04:04.034 : V/rtsp_server(20161) : m=audio 0 RTP/AVP 97

  08-07 14:04:04.034 : V/rtsp_server(20161) : b=AS:29

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=rtpmap:97
  MPEG4-GENERIC/44100/1

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=fmtp:97
  profile-level-id=1 ;mode=AAC-hbr ;sizelength=13 ;indexlength=3 ;indexdeltalength=3 ;
  config=1208

  08-07 14:04:04.034 : V/rtsp_server(20161) : a=control:streamid=1

  Running the same application on Galaxy S2 works since it uses libopencore. But on newer devices it crashes while trying to extract the width and height from the extradata.

  So the problem is with the sprop-parameter-sets.

  My question is why does libstagefright parse the sprop-parameter-sets differently and how could the existing string be converted for compatibility ?

• Convert ffmpeg frame into array of YUV pixels in C

  9 juin 2016, par loneraver

  I’m using the ffmpeg C libraries and trying to convert an AVFrame into a 2d array of pixels with YUV* components for analysis. I figured out how to convert the Y component for each pixel. :

  uint8_t y_val = pFrame->data[0][pFrame->linesize[0] * y + x]; 

  Since all frames have a Y component this is easy. However most digital video do not have a 4:4:4 chroma subsampling, so getting the UV components is stumping me.

  I’m using straight C for this project. No C++. An ideas ?

  *Note : Yes, I know it’s technically YCbCr and not YUV.

  Edit :

  I’m rather new to C so it might not be the prettiest code out there.

  When I try :

  VisYUVFrame *VisCreateYUVFrame(const AVFrame *pFrame){
  
      VisYUVFrame *tmp = (VisYUVFrame*)malloc(sizeof(VisYUVFrame));
  
      if(tmp == NULL){ return NULL;}
  
      tmp->height = pFrame->height;
  
      tmp->width = pFrame->width;
  
  
  
      tmp->data = (PixelYUV***)malloc(sizeof(PixelYUV**) * pFrame->height);
  
      if(tmp->data == NULL) { return NULL;};
  
  
  
      for(int y = 0; y < pFrame->height; y++){
  
          tmp->data[y] = (PixelYUV**)malloc(sizeof(PixelYUV*) * pFrame->width);
  
          if(tmp->data[y] == NULL) { return NULL;}
  
  
  
          for(int x = 0; x < pFrame->width; x++){
  
              tmp->data[y][x] = (PixelYUV*)malloc(sizeof(PixelYUV*));
  
              if(tmp->data[y][x] == NULL){ return NULL;};
  
              tmp->data[y][x]->Y = pFrame->data[0][pFrame->linesize[0] * y + x];
  
              tmp->data[y][x]->U = pFrame->data[1][pFrame->linesize[1] * y + x];
  
              tmp->data[y][x]->V = pFrame->data[2][pFrame->linesize[2] * y + x];
  
  
  
          }
  
      }
  
  
  
      return tmp;

  Luma works but when I run Valgrind, I get

  0x26
  1
  InvalidRead
  Invalid read of size 1

  0x100003699
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  VisCreateYUVFrame
  /Users/hborcher/ClionProjects/borcherscope/lib
  visualization.c
  145

  0x100006B5B
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  render
  /Users/hborcher/ClionProjects/borcherscope/lib/decoder
  simpleDecoder2.c
  253

  0x100002D24
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  main
  /Users/hborcher/ClionProjects/borcherscope/src
  createvisual2.c
  93

  Address 0x10e9f91ef is 0 bytes after a block of size 92,207 alloc’d

  0x100013EEA
  /usr/local/Cellar/valgrind/3.11.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so
  malloc_zone_memalign

  0x1084B5416
  /usr/lib/system/libsystem_malloc.dylib
  posix_memalign

  0x10135D317
  /usr/local/Cellar/ffmpeg/3.0.2/lib/libavutil.55.17.103.dylib
  av_malloc

  0x27
  1
  InvalidRead
  Invalid read of size 1

  0x1000036BA
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  VisCreateYUVFrame
  /Users/hborcher/ClionProjects/borcherscope/lib
  visualization.c
  147

  0x100006B5B
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  render
  /Users/hborcher/ClionProjects/borcherscope/lib/decoder
  simpleDecoder2.c
  253

  0x100002D24
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  main
  /Users/hborcher/ClionProjects/borcherscope/src
  createvisual2.c
  93

  Address 0x10e9f91ef is 0 bytes after a block of size 92,207 alloc’d

  0x100013EEA
  /usr/local/Cellar/valgrind/3.11.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so
  malloc_zone_memalign

  0x1084B5416
  /usr/lib/system/libsystem_malloc.dylib
  posix_memalign

  0x10135D317
  /usr/local/Cellar/ffmpeg/3.0.2/lib/libavutil.55.17.103.dylib
  av_malloc