Reads the voice data and returns the number of bytes written. The compressed data can be transmitted by your application and decoded back into raw audio data using DecompressVoice on the other side. The compressed data provided is in an arbitrary format and is not meant to be played directly. This should be called once per frame, and at worst no more than four times a second to keep the microphone input delay as low as possible. Calling this any less may result in gaps in the returned stream.