QT Pro V VLC

I have just opened a fairly large .avi file (934MB) in QT Pro and it
beachballed for about 15 secs before making it available to watch.
Opening the same file in VLC is almost instantaneous, this behaviour
seems to be the norm. Why the difference ? Is it because QT loads up the
whole file at once and VLC does it " on the fly" so to speak ? I have
noticed that dragging the onscreen timel slider works well in QT but
usually manages to bring up an error in VLC, although this error warning
can just be cancelled and it continues on its merry way. 
-- 
Phil

http://www.philwalters.co.uk