ffmpeg: use actual packet pts when discarding for the copypriorss option

The ist->pts value at this point does not necessarily match the actual packet
pts, which is what should be used to decide whether to discard the packet.
Without this change, some video packets that have pts on or after the start
time are getting discarded when they should not be.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
jpeg2000dec: mct_decode: remove unused return

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
j2kdec:merge mct_decode from jpeg2000

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
j2k/jpeg2000: merge float DWT and related code

the float conditions are largely changed to check the DWT
instead of the bitexact flag, which previously was wrong
(DWT53 is always int)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>