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• Using FFMPEG to extract audio track from video results in extra samples at beginning

  25 janvier 2017, par jreikes

  If I extract audio from a video using ffmpeg -i video.mp4 -c copy audio.m4a, the resulting audio file is slightly out of sync with the original video file. It’s only a tiny fraction of a second, but it causes problems in my application.

  It looks like the audio file gets a few extra samples at the beginning that are ignored in the original video file (not 100% sure, but I think this is what’s happening). I’ve tried a bunch of different seek parameters, but can’t seem to get the audio file to match up properly yet.

  The top waveform is the audio directly from the video file and the bottom waveform is the audio from the extracted audio file.

  

  One of the end goals here was to do an audio crossfade at the beginning of the file. I suspect I stand a better chance of success by doing the crossfade to the original video file instead of separating audio, then doing the crossfade, then re-combining it with the video. I’m currently using the following :

  ffmpeg -i 01.tail.m4a -i 02.mp4 -filter_complex "[0]asetpts=PTS-STARTPTS[a0]; [1]asetpts=PTS-STARTPTS[a1]; [a0][a1]acrossfade=d=0.5" -vcodec copy -mpegts_copyts 1 02.crossfade.mp4

  But the difference in timing is still coming through with this approach and I can hear a short echo during the crossfade. Any idea how to fix this command so that doesn’t happen ?

• Error -138 returns "Error number -138 occurred"

  29 avril 2016, par bot1131357

  I am trying to create a program that listens for a period of time, and then times out so that it can return to work on other tasks and retry again later. Here is the code I am testing with :

  AVFormatContext *pFormatCtx = NULL;
  
  AVCodecContext *codecCtx = NULL;
  
  AVCodec *codec;
  
  int ret = 0;
  
  
  
  // Register all formats and codecs
  
  av_register_all();
  
  avformat_network_init(); // for network streaming
  
  
  
  AVDictionary *d = NULL;           // "create" an empty dictionary
  
  av_dict_set(&d, "timeout", "5", 0); // add an entry
  
  av_dict_set(&d, "rtsp_flags", "listen", 0); // add an entry
  
  
  
  char filename[100];
  
  sprintf_s(filename, sizeof(filename), "%s", "rtsp://127.0.0.1:8554/demo");
  
  
  
  
  
  //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  
  printf_s("Open video file.\n");
  
  // Open video file
  
  ret = avformat_open_input(&pFormatCtx, filename, NULL, &d);   // Returns -138 here 
  
  if (ret <0)
  
  {
  
      printf_s("Failed: cannot open input.\n");
  
      av_strerror(ret, errbuf, ERRBUFFLEN);
  
      fprintf(stderr, "avformat_open_input() fail: %s\n", errbuf);
  
      continue;
  
      //return -1; // Couldn't find stream information
  
  }

  In the listening mode, avformat_open_input() returns -138. Using av_strerror() gives the following explanation : "Error number -138 occurred"

  Is this an Easter egg ? What does -138 stand for ?

• Merge commit ’8606e881b02bec2ac24943d22c8afe11d641fac8’

  12 juin 2015, par Michael Niedermayer

  Merge commit ’8606e881b02bec2ac24943d22c8afe11d641fac8’
  * commit ’8606e881b02bec2ac24943d22c8afe11d641fac8’ :
  
    mpeg12 : Move the vlc bits to a stand alone file
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/mpeg12.h
  • [DH] libavcodec/mpeg12vlc.h