When you open the video page, you'll see a new button on your screen that says "Copy Share Link."
When you click this button, this copies the link to a page that embeds your video from Drive and allows you to track who has signed in to watch your video.
On your video page, you can now also click a button that says "Viewers" and you can see who has signed in to watch your video, how many times they've signed in to watch your video, and the last time they signed in.
Basically, you can get an answer to the question "Who has watched my video?"