I am a iOS developer from China, and I developed a recording application based on AudioUnit. When I tested it on my iPhone6s using the 3.5 mm plug earphone，it worded well and it collected 1024 bytes per frame. But when I tested it on those iPhone which don't have 3.5mm plug, the AudioUnit collected 940 bytes per frame and it reported error.
I tried to test my app on my iPhone 6s using the lightning plug earphone, and it also worked well.
The Remote iOS Audio Unit can change the size of the data in the callback from the requested duration, depending on OS state and audio hardware used.
The difference between 1024 and 940 samples in the callback buffer usually means the Audio Unit is resampling the data from a sample rate of 48000 to a sample rate of 44100 sps. That can happen because the hardware sample rate is different on different iPhone models (48000 on newer ones, 44100 on early models), and your app might be requesting a sample rate different from the device hardware sample rate.
