title: Change volume in only one of the audio channels with FFMPEG
body: <p>I need, in an android application using FFmpeg, to separately adjust the volume of an mp3 file setting two different values for the two channels. 
  This is the command I'm executing:</p>
  
  <pre><code>[-i, 0.mp3, -filter_complex, channelsplit[lpre][rpre];[lpre]volume=0.0[l];
  [rpre]volume=1.0[r];[l][r]amix=inputs=2, 0.wav]
  </code></pre>
  
  <p>In this case for example I'd expect the output to have a mute left channel and the right channel as normal. The result is instead a wave with the same volume on both channels.</p>