Use youtube-dl as a backend
Integrate youtube-dl tool to download videos from numerous supported sites (https://github.com/rg3/youtube-dl/blob/master/docs/supportedsites.md)
This is certainly an interesting idea, but ClipGrab has its own extraction code for all supported video sites. Are there any particular sites you feel are missing from ClipGrab?
I was missing rutube.ru at the moment of writing, but it is low priority for me now.
As Anonymous has commented, youtube-dl includes (almost) everything, but it is missing a GUI. Combination of ClipGrab and youtube-dl would be a really powerful tool. Maybe yt-dl can be used as an optional component if you'd like to keep current extraction methods.
Good idea! There are many sites I miss in Clipgrab and youtube-dl includes everything. It's an incredible list of supported websites there.