SFM Videos in Portal 2 Maps
To be honest, I've seen other responses by iWork925 before, and didn't expect anything really different. I do know he has a lot of respect with the higher-ups in the mapping community, and has his hands in great upcoming projects. I'm not really deterred by his lack of manners toward new people in the forum, but I mean, iWork925...If the only thing you're offering is a snarky negative comment, why not just ignore the post? What you're doing there isn't helping anyone, and isn't necessary. But hey, I'm sure you've heard it all before, and probably don't care.
ANYWAY: Felix Griffin, that was a good idea about just linking the .bik file in the description, I might just end up doing that, if all else fails. Thanks for your continued help 
What if someone wants to play the map but neglects to read the description?
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."
Maybe on the cover art it could say, "Read Description." or the title would include something on reading the description.
Musical website Moddb
that's not too elegant and there might be a few people who wouldn't wanna mess with it that much. but of course the mapmaker could decide to not care about those people.
what are the limitations of making the video into an animated texture? like is there a maximum number of frames you can put on one, do they eat your memory if you have too many, or maybe they just look ugly? I also wanted to do something like this - I will probably never finish that project, but it doesn't hurt to know..
The file size of an animated VTF is proportional to the number of frames, which is added on to the size of your BSP file. The workshop has a very strict limit of (IIRC) 200 megs.
It's fairly easy to set up a script to bring up text on map startup if downloaded files are missing. You could try that. Just set up one script (packed in) which displays the text and closes the map when you leave the elevator, and another (in the download with the movie) which blocks the first one before it can have an effect.
24 frames per second though. It would have to be very short... I guess if someone fails to read the description, I would just let them play the maps without the setup... I agree it lacks elegance putting it in so blatantly... :S
Its actually only 100 MB. 
Like I said before felix went all whiteknight on me, I suggest either doing some sort of trailer type deal with youtube or have a point_viewcontrol look at something in the map.
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."
Alright. I guess that's as much as we can pretend it could have worked 
What I think I'll do is upload it only to TWP initially, so that it can be experienced in its intended way.
Maybe this is a bit much, but could your video be done with point_viewcontrols and prop_dynamics?
Musical website Moddb
I have seen this done before in maps and it can be quite a nice effect. Remember that pbody easteregg in the later wheatley levels.
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."