If the audio file is in a format that's not supported by Avidemux, try re-encoding it to a supported format. You can use tools like FFmpeg or HandBrake to re-encode the file.
Avidemux cannot use audio that is already muxed into a container like .m4a or .mp4 as an external track. It expects the raw stream (e.g., ADTS-encapsulated AAC). avidemux+cannot+use+that+file+as+audio+track
When you see the "Cannot use that file as audio track" error, it usually means If the audio file is in a format
New user getting "Cannot use that file as audio track" - avidemux.org avidemux+cannot+use+that+file+as+audio+track