I have a sorenson compressed quicktime movie with a black
background. The black turns dark gray. If I leave DTS (direct to
stage) turned on the black turns gray. If I turn DTS off the black
stays black. Of course the movie runs too slow with DTS off.
Have you tried other computers. What is your target
environment? This is likely to be caused by the video card -
because DTS uses hardware accelleration. Updating the drivers can
help or some custom setting - this is only helpful however if you
have control over the playback environment.