to embed a video you should just be able to put in the videos youtube url like so
http://www.youtube.com/watch?v=w1AKbUkzgXE
at the moment the feature is only turned on for youtube, dailymotion, google, and vimeo.
The full list of available sites that can be added is
YouTube* YouTube (Playlists) Dailymotion
Google Video Google Maps MetaCafe
Veoh Vimeo Apple Trailers*
Archive.org* Break* Brightcove network
ESPN Facebook* Flickr*
GameSpot Hulu (Usa Only)* IGN
ImageShack JustinTV Kewego network*
Last.fm (Audio) MegaVideo* MSN Live/Soapbox
MySpace Photobucket TinyPic
Yahoo Video*
Video Sites (145) - Select All
123video 5min Life Videopedia 9You
ABC News* AdultSwim AlloCiné
AniBoom Atom* BBC iPlayer (UK)
Bebo* Blip* BoFunk*
BombayTV Broadcaster* CarPix Tv
CBS Sports Cellfish Clarin
Clip.vn ClipFish (Old) ClipFish (New)
ClipJunkie ClipLife ClipMoon
Clipser ClipShack Cold-Link
CollegeHumor ComedyCentral/TDS Crackle
CrunchyRoll* Culture Pub* Current*
Dailyhaha Demoscene.tv* DotSub (w/o Captions)
DoubleViking* dropshots.com Dv.ouou
EASportsWorld* EbaumsWorld Videos* Excessif (DVDrama)
ExposureRoom FunnyOrDie G4TV
GameKyo GameTrailers Gametube.org
GameVideos.1up GarageTv* Gloria
Glumbert GotGame* GrassRoots ItvLocal
GrindTv* Guba TheHub
Humour* Video.i.ua* IMDB*
IndyaRocks Izlesene Jokeroo
Joost JujuNation Video JumpCut
Kaltura network* Koreus Last.fm (Video)
Last.fm (YouTube) Libero LiveLeak
LiveVideo Machinima (Old) Machinima (New)
Video.mail.ru Milliyet* MoFile
Mogulus (Livestream) MotionBox Mpora
Mpora TV MtvU (Usa Only) Multiply
MyNet MySoccerMedia* MyShows.cn*
MyTaratata MyVideo MyVi*
M Thai NhacCuaTui OffUHuge
The Onion* OnSmash PikNikTube
Putfile Rambler RawVegas
Revver RuTube SevenLoad
ShareView Sharkle* Sina Podcast
Smotri Snotr SouthPark Studios
Space.tv.cctv.com Spike Streetfire*
StupidVideos* TagTélé Tangle
Tm-Tube* TrailerAddict* TrTube*
Trilulilu* Truveo* Tu.tv*
Tudou UOL VideoLog UUME
Ustream* u-Tube vbox7
VideoJug* videos.sapo Vidiac
Viddler* Vholdr* Videa
VideoNuz* VidiLife* VidMax
Vidivodo* VSocial (Type1) VSocial (Type2)
Wat.tv* WeGame Wipido*
Yahoo Video HK Yahoo Music Videos Yandex*
YouKu
