. Avidemux generally requires external audio tracks to be in raw or specific formats like WAV, MP3, or AC3 to properly mux them with video. Common Causes Unsupported Containers : You are trying to load an
ffmpeg -i video.mp4 -i audio.m4a -c:v copy -map 0:v:0 -map 1:a:0 output.mp4 avidemux.org Best Practices for Importing New user getting "Cannot use that file as audio track"