title: Multiple audio tracks from one source in ffmpeg
body: <p>I'm transcoding my video using ffmpeg but I am unable to figure out how I can get both a 2 channel aac option (downmuxed) and a surround AC3 option in one go.
  My current command is: </p>
  
  <pre><code>ffmpeg -i input.mp4 \
  -c:v libx265 -preset medium -crf 21 -pix_fmt yuv420p10le \
  -tag:v hvc1 \
  -c:a libfdk_aac -b:a 320k \
  -c:a ac3 -b:a 512k \
  movie_10bit.m4v
  </code></pre>
  
  <p>But I only get surround out of this.
  All help is much appreciated.</p>