[Mp4-tech][Video] Removing macroblocks from the encoded bitstream

[Steve]

Hi all,
I'm working with JM96 encoder and am trying to remove certain macroblocks so
that they don't get added to the bitstream that gets created.
I've got no problems with selecting which ones are removed but am having
trouble finding a nice place in the encoder to remove them. I was thinking
it could probably be done as the stream was written but I can't even find
where this is done despite a lot of searching through the code.
I'm hoping this is one of those cases where it's easy when you know how, any
pointers in the right direction would be very much appreciated!
Thanks in advance,
Steve Beesley,
MEng Hons. DIS