AVI and M4A explained
AVI is a Microsoft container from 1992. It predates modern video compression and lacks features taken for granted today, such as proper support for variable frame rates and modern codec metadata.
M4A is an MP4 container holding only audio — usually AAC, sometimes Apple Lossless. The extension exists mainly so players know not to look for a video track.
- Where AVI files come from
- Old camcorders, legacy Windows software and archived downloads.
- Where M4A is used
- iTunes purchases, Apple Music downloads, voice memos and audiobooks.