What are these UI elements for viewing videos called?

YouTube has this nice functionality, where if you hover over the controls, you can see a preview frame of the time you're hovering above:

Is there a specific name for this kind of preview?

Also, somewhat related: Elgato's Game Capture HD software displays the controls of the video like this:

Where the controls over the video's time are displayed using different frames from the video. Is there a name for this?