How to generate a thumbnail for a YouTube video. 

In order to generate a thumbnail for a YouTube video follow the steps below…….. Well The good news is that you don’t actually have to generate a thumbnail, YouTube actually has several waiting for you:

For eg  if you want to see thethumbnails for :- http://www.youtube.com/watch?v=aq9YSBlo0A8 OR http://www.youtube.com/embed/aq9YSBlo0A8

Here are the images in a couple sizes and frames, note the video id is embedded in the URL:

An easy way to embed the thumbnails in your sidebar would be to enter the image URL manually as a custom field, then customize your theme to display the custom field if it exists.

There is a YouTube thumbnail plugin for WordPress, but I don’t believe it does what I described above. There’s also a jQuery plugin to do the same.