If the file is already MP3 but VBR, try:
You’ve selected an external audio file (like an MP3, WAV, or AAC) to replace or merge with your video’s audio, but Avidemux refuses to cooperate. Why? And more importantly, how do you fix it? avidemux+cannot+use+that+file+as+audio+track
For quickly swapping audio tracks without re-encoding, MKVToolNix is often more flexible than Avidemux for handling various audio containers. How to Properly Add the Track If the file is already MP3 but VBR,
Sometimes, Avidemux simply cannot handle a specific file. It is not a professional audio engineer. If you have spent 20 minutes troubleshooting, consider these alternatives for muxing external audio: If you have spent 20 minutes troubleshooting, consider
If these steps fail, provide:
Once you have this new file, open it in Avidemux to do your final edits.
If none of the above works, your issue is likely with the video track itself, not the audio.