The next version of YouTube video player will have one very useful feature – you can hover your mouse to any point in the video, without actually moving the playhead, and the YouTube player will show you an image thumbnail of the video frame at the position. Thus you can easily get a visual gist of the whole video while the clip is still buffering.
I recorded a screencast video and that should give you a better idea of this new feature.

YouTube Storyboards

YouTube, as you know, generates three thumbnail images to represent a video and these images are captured using the frames at around 1/4, 1/2, and 3/4 points in the video. For instance, if a YouTube video clip is 60 seconds long, the image thumbnails would be generated around frames at the 15s, 30s and 45s mark respectively.
For the new video player, YouTube generates one big Storyboard of 100 thumbnails per video and these thumbnail images are arranged in the Storyboard like a 10×10 grid. As you move your mouse to different points in the video player, it quickly grabs the corresponding thumbnail for that position from the storyboard.
This should save time as you can quickly jump to the most interesting portions of a video based on the scenes shown in the thumbnails. Alternatively, you can skip the video completely if the description doesn’t match the inner thumbnails.
Here are some sample storyboard images that I downloaded from the YouTube website. The new YouTube player was available with quite a few popular videos but not all.