The previous version checked for 14-bit streams and did not properly
work across buffer boundaries.

Use the 64-bit parser state to make extended sync word detection work
across buffer boundary and check the extended sync word for 16-bit LE
and BE core streams to reduce probability of alias sync detection.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>