iOS has various audio frameworks from the higher-level that lets you simply play a specified file, to the lower level that lets you get at the raw PCM data, and everything in between. For our app, we just need to play external files (WAV, AIFF, MP3) but we need to do so in response to pressing a button and we need that latency to be as small as possible. (It's for queueing in live productions.)
Now the AVAudioPlayer and such work to play simple file assets (via their URL), but its latency in actually starting the sound is too great. With larger files of more than five minutes in length, the delay to start the sound can be over a second long which renders it all but useless for timing in a live performance.
Now I know things like openAL can be used for a very-low-latency playback, but then you're waist-deep into audio buffers, audio sources, listeners, etc.
That said, does anyone know of any frameworks that work at a higher-level (i.e. play 'MyBeddingTrack.mp3') with a very low latency? Pre-buffering is fine. It's just the trigger has to be fast.
Bonus if we can do things like set the start and end points of the playback within the file, or to change the volume or even to perform ducking, etc.
The following SO question contains working code that plays a file using Audio Units, and specifically the AudioFilePlayer. Even though the question states that it is not working, it worked out of the box for me - only add a AUGraphStart(_graph) at the end.
The 'ScheduledFilePrime' property of the AudioFilePlayer states how much of the file to load before starting to play. You may want to play around with that.
But as the others note, Audio Units have a steep learning curve.