Avidemux Cannot Use That | File As Audio Track

In the main Avidemux window, look at the (Muxer) dropdown on the left.

Avidemux is not a full-fledged audio workstation. It has strict expectations for audio formats, codecs, and container structures when adding external tracks. avidemux cannot use that file as audio track

When you point Avidemux to an MP4 file with a .m4a extension, you are giving it a box. It doesn't have the built-in tools to open that box to get to the audio inside. The official documentation and moderators on the Avidemux forum have repeatedly confirmed this: Avidemux can only use raw streams as external audio tracks and cannot use audio-only MP4 (M4A) containers, as its demuxer plugins do not support files without a video track. In the main Avidemux window, look at the