In the documentation I see several frameworks for audio. All of them seem to be targeted at playing and recording audio. So I wonder what the big differences are between these?
Audio Toolbox, Audio Unit, AV Foundation, and Core Audio. Or did I miss a guide that gives a good overview of all these?
Check out the "Playing Audio" section of this guide, which gives a good overview of what's what:
Core Audio is the lowest-level of all the frameworks and also the oldest.
Audio Toolbox is just above Core Audio and provides many different APIs that make it easier to deal with sound but still gives you a lot of control. There's ExtAudioFile, AudioConverter, and several other useful APIs.
Audio Unit is a framework for working with audio processing chains for both sampled audio data and MIDI. It's where the mixer and the various filters and effects such as reverb live.
AV Foundation is a new and fairly high-level API for recording and playing audio on the iPhone OS. The first three frameworks are found on both Mac OS and iPhone OS, but AV Foundation is only on the iPhone.