[mythtv] Nuvexport file sizes

[Chris Petersen]

> If i encode something to xvid and it becomes 767 mb, i can't use a
> 80min cd to save it and an 99min would have alot of space free. If i
> could specify that i wanted a file like "870 mb" as a target, i'd get
> the best quailty possible while still getting it onto the same cd.

I can do it for multipass (and it's sort of on the todo list), but not 
for single pass.  you can do it with single pass CBR (constant bitrate), 
but xvid is all VBR (variable bitrate), and thus you need the second 
pass if you want to pick a target filesize.

Once I (or someone else) gets the mpeg (vcd/svcd/etc) modules ported to 
ffmpeg (which seemingly supports multipass mpeg encoding), then it would 
be possible there, too.

-Chris