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• Multiple frames lost if I use av_read_frame in FFmpeg

  12 juin 2015, par Krishna

  I have an HEVC sequence with 3500 frames and I am writing a decoder for reading it (read frame by frame and dump to yuv). In my main(), I have a for loop that calls a decoder() 3500 times (I am assuming at this stage that the main() knows how many frames there are).

  So, for every call to decoder(), I need a complete frame to be returned. This is what the decoder() looks like..

  bool decode(pFormatCtx, pCodecCtx)
  
  {
  
      int gotaFrame=0;
  
  
  
      while (gotaFrame==0) {
  
  
  
          printf("1\t");
  
  
  
          if ( !av_read_frame(pFormatCtx, &packet) ) { 
  
              if(packet.stream_index==videoStreamIndex) {
  
  
  
                  // try decoding
  
                  avcodec_decode_video2(pCodecCtx, pFrame, &gotaFrame, &packet);
  
  
  
                  if (gotaFrame) {  // decode success.
  
  
  
                      printf("2\t");
  
  
  
                      // dump to yuv ... not shown here. 
  
  
  
                      // cleanup
  
                      av_frame_unref(pFrame);
  
                      av_frame_free(&pFrame);
  
                      av_free_packet(&packet);
  
  
  
                      return true;
  
                  }
  
              }
  
          }
  
      }
  
  }

  The behavior is like this : 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 2 1 2 ...... it looks like it reads several frames before decoding one ? The first frame is an I-frame, so shouldn’t that be decoded right away ?

  With this code, I end up losing the several frames (indicated by the series of 1s). Can someone help me out here ? Is there something I am doing wrong in my code ?

  Update : the test clip is video-only. No audio.

• ffmpeg override output file if exists

  30 septembre 2016, par Muhammad Omer Aslam

  i am creating a clip from a audio file (.FLAC) with a start and end time, here is my command.

  ffmpeg -i /audio/191079007530_1_01.flac -t 51 -ss 69 /clips/44z274v23303t264y2z2s2s2746454t234_clip.mp3 2>&1 >> /ffmpegLogs.log

  i use this command with my php code and my question is that when i run this command on the console it asks me to override the output file if the output file already exists in the destination, what switch or extra command should i use to automatically override if the file exists

• FFMPEG force_keyframes multiple / several times

  10 mai 2016, par Johan Skaneby

  I am looking for the correct way to use ffmpeg argument force_key_frames at multiple times in a transcode job. As an example right now I can us force_key_frames 0:00:22 to force a keyframe at 22 seconds, but I need both more granularity forcing at fram level as well as being able to select more time points in the job to have forced key frames.

  Maybe one at 3 minutes 32 seconds 15 frames and another at 8 minutes 16 seconds 11 frames and so on.