I’m on the beta, but have noticed this issue for almost a year.
I like to put a cam image of my driveway up on my phone when I’m expecting someone, but my phone (Essential PH-1 - pretty close to a Pixel 2 and on Android Pie) heats up and goes from 100% battery to 32% in 2 hours, while I can play netflix or youtube videos for many hours.
I’ll go out on a limb and suggest the video is being software decoded and not hardware decoded? That would be a nice feature. When I view the video with tinycam, no battery/warming up but that has options to use HW and HW+ hardware acceleration.