I'd imagine you're thinking about #ensureCloseSema in QuickTimeAudio>>#openMovieFromURI:? It's a rather conspicuous #critical: block.
If you remove that and then delete SophieQuickTimeMovieViaPlugin, then the player you've created in Morphic will play find. I've done it.
Execute this in your image:
and tell me if you see the QuickTime plugin? Hmmm... QuickTime.framework, Carbon.framework, SurfacePlugin...nope, not here. You'll see it listed in the Sophie Dev image, though.
I think the QuickTime plugin signals that Semaphore in #ensureCloseSema for the sake of timing. All the QT plugin does is signal when a frame is complete and ready to go.
In SqueakMovieMorph you set the frame rate automatically to 30 ms. It seems to me the answer to your question depends on what kind of timing mechanism you want for your movie player.
Sophie is a ****ing layered creation. It's extremely professional. I'd be happy if you ripped everything out that you can to distill a simple player, so that I can take that and compare it with Sophie to better understand its onion skins.