I had some troubles getting some client youtube videos to work with the video filter. This was my approach without reading the filters description:
The original video link was embedded in a blog, (e.g.: http://www.youtube.com/embed/S7_MsY2IJz4)
My first approach was to use the /embedd/XXX url with video filter. That didn't work.
So I clicked on the title within the embedded video, which leads to the site http://www.youtube.com/watch?feature=player_embedded&v=S7_MsY2IJz4. Then I used this link which didn't work either, because youtube prepends feature=player_embedded.
If there is a reason/policy why those url format's should not be supported, please let me know. Otherwise i've prepared a patch to allow the embed-syntax and some arguments before the v=-atttribute.