Originally Posted By: Mike Halloran
An m4a contains a video and an audio file.

Mpeg-4 files of the various formats contain video, audio, subtitles, and maybe other data streams within the same single file. A stream is structured data within that file, not a seperate file.

Originally Posted By: Mike Halloran
They are processed separately as others have pointed out.

... or data can simply be discarded if one doesn't want, or cannot allow, that particular data in the output.

Jazz relative beginner, starting at a much older age than was helpful.
AVL:MXE Linux; Windows 11
BIAB2025 Audiophile, a bunch of other software.
Kawai MP6, Ui24R, Focusrite Saffire Pro40 and Scarletts
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