How do music service pages retrieve YouTube video URL?

Question

Music sites like Playmoss and Submissionhub manage to retrieve the YouTube video file URL from the standard player watch URL. When a user pasts a YouTube URL like this into their service, the get the video file URL like this and save them in their system. This is necessary to later reproduce the media files with an external audio player like SoundManager2.

I learned that it's possible to retrieve the info from command line but that's impossible to do so from embedded YouTube videos.

Any idea how the mentioned sites manage to do that?

Answer 1

It is impossible (and illegal) to retrieve YouTube video URL. Music sites like the mentioned in the question seem to play YouTube files controlling the embedded videos. This can be done using Javascript as described here.