This is where many folk discover that re-encoding video often solves it.

But Xvid has far too many settings and options. To figure this out we have to compare that Xvid codec settings to what's in the HDTV's supported codecs.

And no, Samsung has been known to drop stuff like that back to what's in the manual so "it worked before" falls flat. Let's see if that Xvid encoding was in the manual.
Bob