http://www.techsupportalert.com/content ... outube.htm
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Search for the name of a song or band, and the site will bring up the relevant video from Youtube. It'll also automatically analyse the track, work out which chords are being played, and show you them in guitar, ukulele or piano notation.
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http://play.riffstation.com./
I typed in the first thing that came into my head which was 'Black Sabbath Cornucopia', for some reason. It returned a list of youtube vids, I selected the very first one and then hit the 'Get Chords' button. After a few seconds it gave me a list of chords and the option to 'Play' which I did and it played the video and gave a chord chart in real time. WTF?

Here is a list of the chords and another one I analysed -

They got something right coz Tony Iommi tuned his guitars down a Tone and a Half to Csharp for that album I believe. Both of them have the root note correct at least. Very interesting stuff.