[MPlayer-users] Changing aspect ratio within DVD title

[Adam Nielsen]

I've also seen DVDs that do this.  It should in theory be possible, because 
the aspect ratio is encoded into the video, but I imagine it would require 
extensive modifications, which are probably not worth it for the small number 
of titles that make use of it.

Have you instead tried finding the exact locations of the aspect ratio switch?  
Then you could just encode each section manually, e.g. encode the first 
minute as 4:3, then encode the next minute as 16:9, etc. then just join all 
the files together at the end.

Cheers,
Adam.