What exactly is an audio queue processing tap?

Question

These have been around in OS X for a little while now and just recently became available in ios with ios 6. I am trying to figure what they let you do exactly. So the idea is you can tap into an audio queue and process the data before sending it on. Does this mean you can now intercept raw audio coming from different applications and process that (such as the iOS music player) before it plays? In other words is inter-app audio possible? I have read over the audioQueue.h file and can't quite figure out what to make of it.

Answer 1

Consider it a mid-level entry for your audio custom processing (e.g. insert effect) or reading (e.g. for analysis or display purposes) of the queue's sample data. A basic interface for reading or processing an AQ's data.

Does this mean you can now intercept raw audio coming from different applications and process that (such as the iOS music player) before it plays? In other words is inter-app audio possible?

Nope - it's not inter-process; you have no access to other processes' audio queues. These are for your queues' sample data. They can be used to simplify general audio render or analysis chains (the common case, by app count). My guess is that it was provided because a lot of people wanted an easier entry to access this sample data for processing or analysis. Custom processing entries on iOS can also be more complicated to implement (i.e. AudioUnit availability is restricted).