SFM Videos in Portal 2 Maps
Logic_playmovie should automatically do that. A BIK is really the best choice for showing a video, unless you want to painstakingly rebuild your SFM setup in Hammer with tracktrains and func_rotatings.
But, Felix, I was told logic_playmovie's can't be included in maps exported to the workshop...
No, they can't. But it's really your only option, other than using a script to pop up an overlay with a YouTube link.
...YouTube link. 
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."
If you really want to do it that way, I can explain it. But it won't look nearly as nice and will be limited to about 1/4 of the player's screen space (I have no idea what would happen if you used fullscreen mode on the video).
Ya, I'd really rather not do the youtube idea 
I'd either have to find some other way or abandon it completely
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."
Well as long as I have the approval of the great iWork925, then I suppose I can give up. 
1
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."