Why anyone needs raw AAC
For most listening, M4A is the better format: it holds AAC audio plus tags, artwork and an index for seeking. Raw .aac files strip all of that away and keep only the audio frames. Still, some situations call for exactly that bare stream:
- Streaming servers and broadcast tools that take ADTS input.
- Car head units, set-top boxes and cheap players that list .aac but not .m4a.
- Developers who need raw frames for an app, a test or a hardware decoder.
- Video tools that ask for a separate AAC audio track to combine with a picture stream.
If you only want a file that plays everywhere, M4A to MP3 is usually the better choice.
What happens to the audio
This converter decodes the M4A and encodes it again as AAC with the bitrate you choose. That allows you to change the bitrate, sample rate or channels, but it is a second lossy generation for AAC-based M4A files. Choose a bitrate at least as high as the original to avoid an audible loss. For M4A files with Apple Lossless (ALAC) inside, this is a first encode, and any bitrate from 192 kbps up gives excellent results.
| Source M4A | Suggested AAC bitrate |
|---|---|
| Voice memo, about 64 kbps mono | 64 to 96 kbps mono |
| Music, 128 kbps | 128 to 160 kbps |
| iTunes song, 256 kbps | 256 kbps |
| Apple Lossless | 192 to 256 kbps |
What you lose by going raw
Title, artist, album, cover art and chapter markers do not survive, because ADTS has no place for them. Some players show an estimated duration for raw AAC and seek slowly through long files. Gapless information is also lost, so continuous albums may get tiny gaps between tracks. File size stays almost the same at equal bitrate; the container only adds a few kilobytes. Rename the files clearly before converting, since the name will be the only information left. To shorten or edit the audio first, use Cut audio.