Playback analytics show you which students watched a video, how much of the video they watched, and when they first and last watched the video.
From the video's Analytics page, click the MORE button at the bottom
This will provide you with an overview of the video's views. To see who viewed a video, when they watched it and for how long, select PLAYBACK at the top of the screen.
This will show you a list of the folks who have viewed the video, their total number of views, how much they watched (both in time and percentage), and when they first and last watched the video.