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• Mix PCM data from two decoded FFmpeg AVFrame* objects

  15 juin 2016, par williamtroup

  I’m currently using the FFMpeg AutoGen project (in C# of course) to decode frames from an audio file and add them to a new stream that is being written to a video. This all works correctly, but I was wondering how one would go about mixing two AVFrame* objects together (after they are decoded).

  I’ve mixed PCM data before, but was wondering if FFmpeg had a built in API to do the work more effectively.

  This is how I’m currently doing it :

  short* baseFrameBuffer1 = (short*)baseFrame->data_0;
  
  short* baseFrameBuffer2 = (short*)baseFrame->data_1;
  
  
  
  short* readFrameBuffer1 = (short*)readFrame->data_0;
  
  short* readFrameBuffer2 = (short*)readFrame->data_1;
  
  
  
  for (int frameIndex = 0; frameIndex< 1024; frameIndex++)
  
  {
  
      int dataSample1 = GetInRangeSample(baseFrameBuffer1[frameIndex] + readFrameBuffer1[frameIndex]);
  
      int dataSample2 = GetInRangeSample(baseFrameBuffer2[frameIndex] + readFrameBuffer2[frameIndex]);
  
  
  
      baseFrame->data_0[frameIndex] = (byte)dataSample1;
  
      baseFrame->data_1[frameIndex] = (byte)dataSample2;
  
  }
  
  
  
  private static int GetInRangeSample(int sample)
  
  {
  
      if (sample > short.MaxValue)
  
      {
  
          sample = short.MaxValue;
  
      }
  
  
  
      if (sample < short.MinValue)
  
      {
  
          sample = short.MinValue;
  
      }
  
  
  
      return sample;
  
  }

• lavc/huffyuvenc : Move a variable declaration up.

  10 décembre 2017, par Carl Eugen Hoyos

  lavc/huffyuvenc : Move a variable declaration up.
  Fixes a warning with gcc-6.3 :
  
  libavcodec/huffyuvenc.c:93:5 : warning : ISO C90 forbids mixed declarations and code
  

  • [DH] libavcodec/huffyuvenc.c

• FFmpeg : Combine video files with different start times

  18 mai 2016, par Fabian

  I have two webm files with audio and video recordings of a video conference session. Both files only contain one side of the conversation. They are not of the same length (someone has joined before the other one), but I have the unix timestamp in milliseconds of the start time of each video file.

  On a timeline they look like this :

  webm 1:   -----------------------------------------------
  
  webm 2:                 -----------------------------

  or like this :

  webm 1:   -----------------------------------------------
  
  webm 2:                          -----------------------------

  I would like to combine these two video files into one file so that :

  1. They appear next to each other (using the hstack option), and
  2. That they are mixed with taking the time stamps of the start times
     into account. The final video should then look like this :

  Target result : --------------===========================----

  The beginning and the end of the new video would show a black placeholder for the video file that has no data at this time of the mixed stream.

  At the moment I use this command :

  ffmpeg -i 1463408731413703.webm -i 1463408880317860.webm -filter_complex \
  
  "[0:v][1:v]hstack=inputs=2[v]; \
  
   [0:a][1:a]amerge[a]" \
  
  -map "[v]" -map "[a]" -ac 2  -c:v libvpx output.webm

  This creates a video like this :

  Not good result : =====================------------------

  i.e. the conversation is out of sync.

  How can I combine two video streams with different length and different start times using ffmpeg so that I will end up with "Target result" above ?

  Thanks a lot !