[mythtv] Another commercial flagging method

[Liam]

I've been experimenting with commercial detection some more and I think I have a pretty good method now. It looks for suspicious events in the form of blackframe scenes of a standard length and scenechanges at ten second boundries. Then it tries all combinations of blackscene-bordered intervals and gives them a rating based on their length and the number of events they capture. After a bit of tidying of unusually long or short intervals the rest are used for the cutscenes. It can be foxed when a show starts with "here's what happened last week ... blackframe" but apart from that it seems pretty good. I don't know how well it would cope with NTSC as it wants to be within two frames for the ten-second test and the framrate doesn't fit well with integers. Any thrashing is appreciated, the patch needs to be applied to fresh cvs.

Liam