MP3 vs M4A (AAC): what is the audio codec for portable devices which gives maximum independence?
If you plan to use your audio files on more than one portable player, especially if you want to use them on future players that you haven't bought yet (so you don't know what formats they will support), MP3 is more or less your only option. Even for players with support for other formats, that support is often incomplete and buggy.
Unless you make sure to only buy Rockbox-compatible players. Then you can use pretty much any format you like.
Of course, the only truly future-proof solution is keeping lossless copies of everything and transcoding to lossy formats for mobile players.
AAC is in very widespread use today. For example, Internet video streams are usually encoded in H.264, and usually uses AAC for its audio. Almost any modern portable media player is able to play back both MP3 and AAC.
However, there are two things to take into account:
- AAC is the more efficient codec, meaning that it takes less storage space (=bitrate) for the same audio quality (or the same bitrate for better audio quality). So, from a purely quality-oriented point of view, AAC is plain better and support is widespread enough to give it a go.
- AAC is slightly more complex than MP3, which may lead to a slightly higher computational load and hence, slightly decreased battery life especially on older devices. However, higher bitrates generally decrease battery life, too, so this is only a valid argument for MP3 files and AAC files of similar bitrates.
Overall, I would use AAC without hesitation.
(If you want to know more, I posted something about audio quality of MP3s and AAC files a while ago.)
MP4/M4A (both are AAC based files) render much better at lower compressions. A 128kB range AAC file stomps mp3 in the dirt in sound quality. Above 220, a little less so, but still way better. If you are trying to cram thousands of songs into a limited storage space, AAC will put a smile on your face. If you have a huge mp3 collection and most of it is above 260kB, don't waste your time converting them; just go with what you already have for now. If you are starting from scratch or are working on a new database (taste in music changed over the years) go AAC. More devices will support them in the future. Several major music hardware manufacturers already include AAC decoding on their devices. AAC -IS- a better compression engine than mp3. There were lots of cassette tapes around at one time; where are they now? In museums. Bye bye mp3.