sired positioning of the new stream must occur before the call to
ov_crosslap() as a seek dumps all prior lapping information from a
stream's decode state.  Crosslapping does not introduce or remove any
extraneous samples; positioning works exactly as if ov_crosslap was not
called.

<p>ov_crosslap will lap between streams of differing numbers of
channels. Any extra channels from the old stream are ignored; playback
of these channels simply ends. Extra channels in the new stream are
lapped from silence.  ov_