Retrieves the current position and value of an envelope on a mixer source channel.
|handle||The channel handle.
|type||The envelope to get the position/value of. One of the following.
|value||Pointer to a variable to receive the envelope value at the current position... NULL = do not retrieve it.
If successful, the current position of the envelope is returned, else -1 is returned. Use BASS_ErrorGetCode to get the error code.
|BASS_ERROR_HANDLE||handle is not a mixer source.
|BASS_ERROR_ILLTYPE||type is not valid.
|BASS_ERROR_NOTAVAIL||There is no envelope of the requested type on the channel.
During playback, the envelope's current position is not necessarily what is currently being heard, due to buffering.