Few months ago I collecting some free PHP scripts to create social networking site, yes maybe with common social networking feature the video sharing must be included there, but all this scripts that I mention from the start focusing just for video sharing site.
The community edition of Vimp available for free download and free just for personal and non-commercial use. The ViMP flash player can also be integrated into other webpages without the slightest effort, due to the automatically generated embed code
Clip bucket is one of the most popular video sharing script based on PHP, you can see on the clipbucket showcase page to see many live sites running on clipbucket.
PHPmotion start as video sharing script, but when I see the features, there are more features that can be used as common social network like image gallery, blogs, audio,
VidiScript is a video sharing site that is packed with features that you can only find on major media sharing communities like YouTube, Meta Cafe, Daily Motion and Break.
Dentro Video is a joomla CMS plugin, so you need joomla running to install this script.