This extension for Google Chrome will add a button next to your URL bar where you can easily download videos from most of the websites. Unfortunately it doesn't work on Youtube, but it works on Dailymotion, Vimeo etc.
To change a file format just edit the file extension when the download dialog appears. For example, change the ".mp4" video extension to ".mp3" for audio only format.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.