Apple has removed that features in Snow Leopard and QuickTime X has no preferences panel to enable this. So you need to go through the command line to get it back...

In Terminal, copy/paste:

defaults write MGPlayMovieOnOpen 1

Now movies will autploay when you double click them.

Comments from long ago:

Comment from: Bredbånd

This actually worked for me, so thanks a lot for the info :)

2010-08-09 12-10

Comment from: Isaiah

WOW. THANKS for the the post. I was looking for a solution to this for a long time. It works.

2010-08-29 05-56