When opening recent replays such as in http://bwreplays.com/ I cannot see any 78 9C magic numbers.
What I have in common when comparing header of two replays is :
a77e 7e2b 0100 0000 0400 0000 7265 5253
or in other terms:
b'\xa7~~+\x01\x00\x00\x00\x04\x00\x00\x00reRS'
Does anyone can help tell what compression it is?