netbsdnoob As you've introduced me to Vulfpeck, I'll try to help you.
Download the video using
youtube-dl, then play it locally using
mpv. Press I. How many frames are dropped?
Using my lowest CPU frequency, 800 MHz, playing Dean Town, I see 7 output frames dropped at the end of the video with
vo=sdl, and 425 dropped output frames with
vo=xv (the default), but, no noticeable slowdowns in either case.