I use Linux (Kubuntu 16.04), and I have some .MP4 files with audio tracks, which I want to extract, save as .AAC/.M4A files and tag.
Now, I've been doing the extraction using
MP4Box -raw $track_index my_file.mp4
where the track index can be 0, 1, 2 etc. This works, since I can play the result in various media players... but - does it, really?
Someone who looked at my files told me:
the "ftyp" field is missing from the head of the file, which would identify it as an MPEG 4 container. There are also no "mdat" fields, which would indicate individual chunks of data inside an MPEG 4 container.
and this makes it difficult for certain apps to work with my extracted files. Specifically, tagging apps... which refuse to write tags for it.
What can I do to get properly-structures, taggable M4A/AAC files? (I'm looking for a command-line solution naturally.)