[mythtv] mythtranscode -> avi

[Chris Petersen]

> Not quite true, with my windows filters it's posibel to convert a nuv file
> to avi without any kind of recompression.
> There's no fancy gui for it (yet) so you have to use graphedit and build the
> filter graph manualy.
> But maybe you were refering to a linux solution.

Yes, I need a linux solution in order for this to be useful for nuvexport.

avidemux2 seems like it might work, but it's HORRIBLY slow, and I'd much 
rather have something within myth, in case the format changes again.

-Chris