I understand YT counts it as a view if I watch a video for 30sec or more. But what I'm curious about is how YT can tell what I actually watched versus the amount of video YT sent me & was spooled up on my PC?

E.g., I'm using a Windows laptop & Chrome browser. I click on a video & let it play for 11secs & then paused it. By that point, YT had sent about 1min worth of video data as shown by the play progress bar at the bottom of the video window. Within a few seconds, YT sent additional data while I was paused to total 7m33s of video. I then pulled my ethernet cable out, turned off the channel & reconnected ethernet.

I believe YT thinks I saw 7m33s tho I only watched 11s. Because how can YT see what I actually did with the video data?