Google is adding Instant Previews for Videos. Instant Previews for videos have the same appearance as regular Instant Previews -- the selected clip is highlighted in blue and a clickable magnifying glass appears next to the title of the video. But rather than see a preview page of a website, you'll see four short playable clips from a video.
By default, there is no sound, so you'll have to enable it by clicking the small blue x next to the volume icon in the top left. You can either let the clips play by themselves, or mouse over a clip you want to preview. Clicking on the preview will take you directly to the full video.
Instant Previews appear in universal search results, or under Google Videos. Video providers must opt to make previews available, so not all videos will have this option yet.
Google also added Instant Previews for mobile last week.