Position cursors, expressed as a byte offset, are maintained on sound and capture buffers indicating where it is safe to write or read data and the data currently being played or captured.
The read cursor is used in capture buffers, following the capture cursor and indicating the beginning of the block currently being captured. The buffer area between the read and capture cursors is currently recieving sound data and as such cannot be read safely.
Data may be safely retrieved from the buffer up to the current position of the read cursor.
The read cursor moves with the capture cursor, not with any data being retrieved from the buffer. Thus it is neccessary for your application to maintain its own pointer for the purpose of reading data from the buffer.