Audio is showing up in mediainfo and plays in VLC
- Most likely this is a MPEG TS file and does not contain PAT/PTM so brute force is used to detect the tracks. Brute force is not very good at detecting audio
- Use mkvmerge to convert it to a mkv (it's very fast, no quality loss at all)
the resulting mkv can be opened without troubles
source: No audio tracks showing up (but audio plays in VLC) (http://avidemux.org/smif/index.php/topic,17614.msg79956.html#msg79956)
Pass video through mkvtoolnix (https://mkvtoolnix.download/), then loading the newly saved .mkv has avidemux detecting the audio track.