Any kind of text over video you do in QuickTime will require some
compositing, and from the sounds of it QuickTime itself may not be
doing it as fast as it can be done. Another thing that can cause huge
problems is if the text is somewhere else on the disc, and also not
preloaded. The playback would spend a lot of time seeking to get the
next chunk of text.
Normally if you have text tracks in the movie you ought to set the
track preload to true, then do a save as to a new self contained
file. The text will then be at the start of the file and will preload
into memory, leaving the real time playing only having to deal with
the video and sound.
There is another way to go though. Since system 10.3, maybe earlier,
QuickTime performance improved a lot, possibly because of Quartz
Extreme. You can play two full frame rate movies with transparency
changing in Director, with them set to be non direct to stage, and
get away with it. Playing one opaque non-DTS movie is very easy, and
you can then place a Director Text member on top of the video, and
get good playback with anti-aliased text on top of the video.
For getting the text to synchronize you could export the text track
with the time descriptors and then use that time code info in
Director to change the text at the right time. It's fairly easy to do
all of this.
