B-MAC HACK

Heres a basic rundown. BMAC consists of three time multiplexed
components. First is the luminance which occupies 2/3 of what would be
the active video portion of a PAL signal. The other 1/3 is used to
convey the chromance component. The blanking portion of the line (where
the sync signal would normally be) carries the data stream at just over
20 Mhz bit rate. Scrambled BMAC varies the length of this data burst in
a pseudo random manner giving rise to the zig zag pattern you see on the
screen. SBS on the otherhand is a non-scrambled BMAC signal and the
picture is easily obtainable using a sync generator.   The scrambled
video can be obtained by first digitising the video signal and passing
it through a variable length FIFO register. The active video is
recognised as beginning at the end of the data burst, therefore
detecting the length of the data burst gives you the delay required to
restore the video, along with a sync inserter.There are a couple of
things to be wary of in this technique, such as periods of no data burst
and gaps after the burst. With a bit of imagination these are simple to
overcome also. A simple way to test these techniques is to use a
digitiser and haul the data into your computer, where you can implement
ideas in software. Works a charm. Once you have it sussed, you can
duplicate the software in hardware.