Dear lazyweb...
What's the best way to rotate an MPEG movie through 90˚?
My understanding is that JPEGs can be rotated through 90˚ losslessly, so I assume that this can be done losslessly for MPEGs too, and I hope with a command-line tool.
mencoder -vf rotate=1 -o out.mpg -oac copy -ovc lavc in.mpg