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• How to sum audio from two streams in ffmpeg

  9 février 2021, par user3188445

  I have a video file with two audio streams, representing two people talking at different times. The two people never talk at the same time, so there is no danger of clipping by summing the audio. I would like to sum the audio into one stream without reducing the volume. The ffmpeg amix filter has an option that would seem to do what I want, but the option does not seem to work. Here are two minimal non-working examples (the audio tracks are [0:2] and [0:3]) :

  


  ffmpeg -i input.mkv -map 0:0 -c:v copy \
       -filter_complex '[0:2][0:3]amix' \
       output.m4v

ffmpeg -i input.mkv -map 0:0 -c:v copy \
       -filter_complex '[0:2][0:3]amix=sum=sum' \
       output.m4v


  


  The first example diminishes the audio volume. The second example is a syntax error. I tried other variants like amix=sum and amix=sum=1, but despite the documentation I don't think the sum option exists any more. ffmpeg -h filter=amix does not mention the sum option (ffmpeg version n4.3.1).

  


  My questions :

  


  


  1. Can I sum two audio tracks with ffmpeg, without losing resolution. (I'd rather not cut the volume in half and scale it up, but if there's no other way I guess I'd accept and answer that sacrifices a bit.)

     


  


  2. Is there an easy way to adjust the relative delay of one of the tracks by a few milliseconds ?

     


  


  


• Using Node.js module fluent-ffmpeg to convert video but my files end up corrupt

  19 septembre 2013, par El Guapo

  i am writing a node based media encoding tool and have found a few good node packages that will help me to do this, but the output files are either totally corrupt or it only encodes half the video.

  The main node package i am using is fluent-ffmpeg, and i am trying it with the following code :

  var ffmpeg = require('fluent-ffmpeg');
  
  
  
  var proc = new ffmpeg({ source: 'uploads/robocop-tlr1_h480p.mov', nolog: false})
  
    .withVideoCodec('libx264')
  
    .withVideoBitrate(800)
  
    .withAudioCodec('libvo_aacenc')
  
    .withAudioBitrate('128k')
  
    .withAudioChannels(2)
  
    .toFormat('mp4')
  
    .saveToFile('output/robocop.mp4',
  
      function(retcode, error){
  
          console.log('file has been converted succesfully');
  
  });

  There is not a problem with the source video as i encoded it just fine using FFmpeg normally with the following comand line string (i run it from a batch file) :

  "c:\ffmpeg\bin\ffmpeg.exe" -i %1 -acodec libvo_aacenc -b:a 128k -ac 2 -vcodec libx264 -b:v 800k -f mp4 "../output/robocop2.mp4"

  Any ideas what i am doing wrong here ?

• Using Node.js module fluent-ffmpeg to convert video but my files end up corrupt

  28 juin 2017, par El Guapo

  i am writing a node based media encoding tool and have found a few good node packages that will help me to do this, but the output files are either totally corrupt or it only encodes half the video.

  The main node package i am using is fluent-ffmpeg, and i am trying it with the following code :

  var ffmpeg = require('fluent-ffmpeg');
  
  
  
  var proc = new ffmpeg({ source: 'uploads/robocop-tlr1_h480p.mov', nolog: false})
  
    .withVideoCodec('libx264')
  
    .withVideoBitrate(800)
  
    .withAudioCodec('libvo_aacenc')
  
    .withAudioBitrate('128k')
  
    .withAudioChannels(2)
  
    .toFormat('mp4')
  
    .saveToFile('output/robocop.mp4',
  
      function(retcode, error){
  
          console.log('file has been converted succesfully');
  
  });

  There is not a problem with the source video as i encoded it just fine using FFmpeg normally with the following comand line string (i run it from a batch file) :

  "c:\ffmpeg\bin\ffmpeg.exe" -i %1 -acodec libvo_aacenc -b:a 128k -ac 2 -vcodec libx264 -b:v 800k -f mp4 "../output/robocop2.mp4"

  Any ideas what i am doing wrong here ?