// move all the buffers on the track's fifo to our internal
// fifo so that (a) we don't deadlock in the reader and
// (b) we can control how data from multiple tracks is
// interleaved in the output file.
// move all the buffers on the track's fifo to our internal
// fifo so that (a) we don't deadlock in the reader and
// (b) we can control how data from multiple tracks is
// interleaved in the output file.