Trailer Mash-Ups: From Whence the Trailers?

I may be blind here, but when people produce genius works like this (The Shining as rom-com), I assume they’re working from trailers and not recording or grabbing clips from the actual movie. If so, are they downloading from production house sites (though most seem to only let you watch online)? Grabbing stuff off of DVDs?

Not so inconceivable, I know, but some clips are watchable on full-screen (whereas I have fully seen TV shows that were obviously produced by recording a TV screen with a handheld camera).

So- is there some treasure trove of high-res movie trailers I don’t know about?

I would think that in most cases they are pulling scenes from the movie itself on DVD. It’s easy enough to do. For example there’s one with video from Toy Story and audio from Requiem for a Dream, and it has scenes that aren’t from any trailer as far as I know.

My cable company has a trailers-on-demand feature. It’s high up in the digital channels, but I don’t think it’s high-def, so it would be (relatively) trivial to capture to an MPEG for editing.

Considering the low quality of the typical distribution (i.e. the video compressed down so youtube can carry it), a bit of quality loss in the editing isn’t going to matter.