ClipGrab is a free software for downloading and converting online videos from many sites like YouTube or Vimeo. ClipGrab can download from the following sites: YouTube, Clipfish, Collegehumor, Dailymotion, MyVideo, MySpass, Sevenload, Tudou, Vimeo. Downloaded videos can be converted to the following file formats: WMV, MPEG4, OGG Theora, MP3 (audio only), OGG Vorbis (audio only).
Visit the official site for more info: http://clipgrab.de/en
To install ClipGrab in Ubuntu Open the terminal and run the following commands:

sudo add-apt-repository ppa:clipgrab-team/ppa
sudo apt-get update
sudo apt-get install clipgrab

Open Clipgrab
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Visit the official site for more info: http://clipgrab.de/en