libfaac is a safe aac default, but aacplus works MUCH better at the the 8 - 16 kbps range, which seams to be a stated goal of this page. It turns on SBR+PS and has ffmpeg support.
If any Dropbox people are reading this, can you comment on what criteria you used to pick the audio codec?
You correctly guessed that we picked libfaac as a safe option for compatibility. I never tried out aacplus and sounds indeed interesting so we'll likely try it out soonish. Our target rate is a bit higher than those you mention though. For audio, we target 32kbps at low quality layers and 96kbps at higher qualities. Couple of questions for you:
- how does aacplus works at these rates?
- what compatibility issues can we expect if we were to try it out?
If any Dropbox people are reading this, can you comment on what criteria you used to pick the audio codec?