The generic extractor will add it.
IE_DESC = u'YouTube.com'
_VALID_URL = r"""(?x)^
(
- (?:https?://|//)? # http(s):// or protocol-independent URL (optional)
+ (?:https?://|//) # http(s):// or protocol-independent URL
(?:(?:(?:(?:\w+\.)?[yY][oO][uU][tT][uU][bB][eE](?:-nocookie)?\.com/|
(?:www\.)?deturl\.com/www\.youtube\.com/|
(?:www\.)?pwnyoutube\.com/|
)
))
|youtu\.be/ # just youtu.be/xxxx
- |https?://(?:www\.)?cleanvideosearch\.com/media/action/yt/watch\?videoId=
+ |(?:www\.)?cleanvideosearch\.com/media/action/yt/watch\?videoId=
)
)? # all until now is optional -> you can pass the naked ID
([0-9A-Za-z_-]{11}) # here is it! the YouTube video ID