I've often wondered how to glom the image that's shown at the start of a YouTube vid. Here's the template.
http://img.youtube.com/vi/VIDEOID/0.jpg
Just substitute the video id for VIDEOID in the url template above. For example, for this vid:
http://www.youtube.com/watch?v=9HQZ_t1MSWk
...the url of the top image is:
http://img.youtube.com/vi/9HQZ_t1MSWk/0.jpg

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