title: How to convert AC3 to AAC on Windows from the CLI
body: <p>I have a large number of MKV files with AC3 tracks that I want to re-encode to include an AAC track using a script. My current approach has been to extract the AC3 track (mkvextract) and attempt to re-encode that as AAC and then merge that back in (mkvmerge). Thus far I've been able to script the extraction (MKVTools and Powershell helped there) but I cannot find a way to convert AC3 to AAC.</p>
  
  <p>I've tried creating a fake MP4 file with mp4box and an "empty.h264" file (from code.google.com) but when that's presented to handbrake_cli, the short video input causes handbrake to barf. I tried a similar thing with avidemux (2.6.9) (both from the CLI with avidemux2 and GUI) but again, the very short video track causes it to fail in creating a proper new target.</p>
  
  <p>If Handbrake had a "pass-through" mode for video, I'd just use that and add a second audio track that was converted from AC3 to AAC but alas handbrake doesn't do pass-through video.</p>
  
  <p>What am I missing? Is there a solution to this problem?</p>