I suggest this Improved that allready has JomSocial:
1. User1 add video link with stream or at video gallery.
2. User1 add the same video link.
Result 1: User can see the mesasge that this video was added before (and link to this video).

But you can make extra option
3. User2 add the same video link.
Result 2: User2 get notice that User1 allready added video with this link (this video allready on the site).

Thanks.