Actually I link all the videos from Youtube. Is there any options to view all the videos in one gallery. Suppose if it possible what kind of extension to be installed and how. Now I currently installed Allvideos Joomla k2 extensions. But it asks the video path.

Hi. AllVideos will not give you a list of all videos of your site. You can use a tag like "video" for example to tag all items that contain video and then create a menu link to this tag.