Get the current position of the source associated with this playing ID, obtained from PostEvent(). Notes:
You need to pass AK_EnableGetSourcePlayPosition to PostEvent() in order to use this function, otherwise it returns AK_Fail, even if the playing ID is valid.
The source's position is updated at every audio frame, and the time at which this occurs is stored. When you call this function from your thread, you therefore query the position that was updated in the previous audio frame. If in_bExtrapolate is true (default), the returned position is extrapolated using the elapsed time since last sound engine update and the source's playback rate.
AK_Success if successful. It returns AK_InvalidParameter if the provided pointer is not valid. It returns AK_Fail if the playing ID is invalid (not playing yet, or finished playing).