Previously only 1:1 bitstream filters were supported, the end of the stream was
not signalled to the bitstream filters and time base changes were ignored.

This change also allows muxers to set up bitstream filters regardless of the
autobsf flag during write_header instead of during check_bitstream and those
bitstream filters will always be executed.
Signed-off-by: Marton Balint <cus@passwd.hu>