If Avidemux refuses to merge the audio and video tracks internally, you can bypass the issue entirely by using an external multiplexer (remuxer). is the best tool for this, as it combines tracks without losing quality or re-encoding. Download and open MKVToolNix GUI .
"cannot use that file as audio track" in Avidemux typically occurs because you are trying to import an audio file that is wrapped in a (like .m4a or .mp4) rather than a raw stream avidemux cannot use that file as audio track
The error is almost always a metadata or bitrate formatting issue. By converting your audio to a Constant Bitrate (CBR) format or forcing Avidemux to re-encode the audio (rather than using "Copy" mode), you can usually resolve the conflict in seconds. If Avidemux refuses to merge the audio and