Here's some content related to the error "Avidemux: Cannot use that file as audio track":
To fix the "Cannot use that file as audio track" error in Avidemux, you typically need to convert your audio into a raw format or a simpler container. Avidemux often fails to import audio tracks that are already muxed into modern containers like avidemux.org 1. Unsupported File Containers avidemux+cannot+use+that+file+as+audio+track
The Fix: If you are trying to use a FLAC or Opus file as an external track, you must change your output format to MKV. MP4 does not support FLAC natively. Here's some content related to the error "Avidemux:
If MKVToolNix rejects your audio file, your file is truly corrupted. If MKVToolNix accepts it but Avidemux doesn’t, then Avidemux is the bottleneck. then Avidemux is the bottleneck.