Unexpected behavior with AudioQueueServices callback while recording audio

Question

I'm recording a continuous stream of data using AudioQueueServices. It is my understanding that the callback will only be called when the buffer fills with data. In practice, the first callback has a full buffer, the 2nd callback is 3/4 full, the 3rd callback is full, the 4th is 3/4 full, and so on. These buffers are 8000 packets (recording 8khz audio) - so I should be getting back 1s of audio to the callback each time. I've confirmed that my audio queue buffer size is correct (and is somewhat confirmed by the behavior). What am I doing wrong? Should I be doing something in the AudioQueueNewInput with a different RunLoop? I tried but this didn't seem to make a difference...

By the way, if I run in the debugger, each callback is full with 8000 samples - making me think this is a threading / timing thing.

Answer 1

Apparently, from discussing with others — and the lack of responses, this behavior is as designed (or broken but not likely to be fixed), even if improperly documented. The work around is to buffer your samples appropriately in the callback if necessary and not expect the buffer to be full. This isn't an issue at all if you are just writing the data to a file, but if you expect to operate on consistently sized blocks of audio data in the callback, you will have to assure this consistency yourself.