dialog object freezes movies?

You might be asking two different questions.

Caution in reading my response -- These are solutions based on lots of trial/error from a while ago (as far back as v4). There might be more up-to-date solutions.

Regarding the Dialog:

I'm not sure what the right answer is for using [dialog]. I wrote a surrogate dialog patch many years ago that I still use with no problems. You'll have to adjust it for your purposes.

http://www.hellbender.org/ikehmope.html and download ike.dialoger

It's Max v4, so hasn't been tested in a while, but I'm using its descendent in v5 with no problems.

You can alos pre-populate [ubumenu] objects with path/file information and use it to load movies. Means you need to know your directories in advance (though there are ways to use [ubumenu] to first select a path, then populate another [ubumenu] based on that path). I can't post an example, the patches I've written aren't self-contained enough.

Regarding the momentary freeze:

In my experience, this is unavoiable the first time a movie is loaded (maybe other people know how to resolve the issue).

If I reload the movie later (e.g., load movie 1, then movie 2, then go back to movie 1), it won't stall the patch because enough of it has been cached somewhere.

Consider loading/unloading all movies prior to actually working with the patch. You can write a patch that will do that if you know all your target movies in advance. Doing it manually has worked for me.