My understanding is that the AudioTrack provides basic audio playback support of actual sound files only. JetPlayer supports MIDI files which is not an actual audio file but a reference file that instructs the software how to play the sound and what sound processes to use. No encoded sound in the MIDI file itself.
By utilizing typical MIDI file support, you can load and access 16 or more MIDI tracks which references individual sound files for playback in each track. Audiotrack handles only one audio source.
Also, JetPlayer itself has more flexibility on how the output is manipulated. For example, selecting a section of the sound as a clip allows you to play the clip once or looped.
Bob
Jetplayer also includes a virtual instrument, so sound-design developers like myself can use it to create a sound library for Android. Known as a rompler, the Jetplayer will allow you to load in samples and then convert that to a Android-readable file, complete with definitions of how and when to use the sounds.
I have a large library of sounds that I have created over the years and I would love to port them and new sounds to a sound app for Android to compete with iPhone apps with similar functionality.
I do plan to also create some virtual instruments/apps that will allow for sound and perhaps even image synthesis.
This is all very exciting.
My take is that the more audio possibilities you build into basic4android, the better. In the end, the most important thing is latency and memory management - the least amount of latency possible so sounds play immediately and memory management so you can add more sounds and play them simultaneously without causing distortion due to buffer errors (or the buffer being to small/large).
Audiotrack sounds perfect for building an app like Acid where you playback multiple tracks of audio.
JetPlayer sounds perfect for creating virtual instruments and sample playback apps (that I would also add synthesis to).
Mike