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• What happens if I ffmpeg encode two times successively with the same bitrate

  3 juin 2019, par a a

  I have a original divx video (3500k) which I encode to h.264 in a mp4 container. I choose to encode it with 1000 k for instance so that the quality stays close to the original. What happens if I encode it then one more time with the same bitrate ? Theoretically should the quality stay the same ?

  ffmpeg -i A.divx -an -vcodec h264  -b:v 100k A.mp4

• ffmpeg mod if case in source code

  5 février 2014, par Stephan Pokorny

  I'm working on a specific ffmpeg mod where I have to auto execute an extension within the binary call.

  Specific it is the extension -isync -af aresample=async=1000

  The binary is called by another compiled tool which escapes my input.

  For that reason I wanna rewrite the filter rule to execude in any case.

  if (audio_sync_method > 0) {
  
      char args[256] = {0};
  
  
  
      av_strlcatf(args, sizeof(args), "async=%d", audio_sync_method);
  
      if (audio_drift_threshold != 0.1)
  
          av_strlcatf(args, sizeof(args), ":min_hard_comp=%f", audio_drift_threshold);
  
      if (!fg->reconfiguration)
  
          av_strlcatf(args, sizeof(args), ":first_pts=0");
  
      AUTO_INSERT_FILTER_INPUT("-async", "aresample", args);
  
  }

  Can somebody help me to execute this AUTO_INSERT_FILTER in any case which could happen.

  I already played around to answer any if loop with the AUTO_INSERT_FILTER_INPUT("-async", "aresample", 1000) ;

  When I launch I can see that it is calling the fresh compiled version of ffmpeg but not activating the filter

  Thanks

  Stephan

• Strange performance of avcodec_decode_video2

  26 janvier 2014, par John Simpson

  I am developing an Android video player. I use ffmpeg in native code to decode video frame. In the native code, I have a thread called decode_thread that calls avcodec_decode_video2()

  int decode_thread(void *arg) { 
  
     avcodec_decode_video2(codecCtx, pFrame, &frameFinished,pkt);
  
  }

  I have another thread called display_thread that uses aNativeWindow to display a decoded frame on a SurfaceView.

  The problem is that if I let the decode_thread run continuously without a delay. It significantly reduces the performance of avcodec_decode_video2(). Sometimes it takes about 0.1 seconds to decode a frame. However if I put a delay on the decode_thread. Something likes this.

  int decode_thread(void *arg) { 
  
      avcodec_decode_video2(codecCtx, pFrame, &frameFinished,pkt);
  
      usleep(20*1000);
  
  }

  The performance of avcodec_decode_video2() is really good, about 0.001 seconds. However putting a delay on the decode_thread is not a good solution because it affects the playback. Could anyone explain the behavior of avcodec_decode_video2() and suggest me a solution ?