Record the audio from Device itself

[rsZWang]

I need to analyze the audio played by device itself
That means I play and record simultaneously

So I set audioSession like this:
try audioSession.setCategory(.playAndRecord, mode: .videoChat, options: .defaultToSpeaker)

But there is always a warning from this:
assert(remainderf(sizeFloat, powf(2.0, lg2)) == 0, "size must be a power of 2")
It seems that the buffer will be effect when the audioSession set

I can modify the buffer size by try audioSession.setPreferredIOBufferDuration(0.1)
But the size always can not be power of 2

How can I fix this problem?
Thanks