The last metadata format in this comparison series will be metadata for AAC audio files,
which are usually included in an MP4 container (see MPEG-4 Part 14).
MP4 audio files can have various file extensions, most commonly m4a, but also mp4 or m4b (for audio books).
So let the confusion continue ...
Podcast Comparison, Part 4: MPEG-4 iTunes-style Metadata (AAC Audio, M4A, MP4)
Written by on in Audio.