I usually don't like to rag on bad but highlight good, but in reddit's video player they are obviously doing too much tracking in it or it was rushed because it is not responsive many times even on a fast connection on a massive desktop machine. It is hard to seek, hard to play/stop/pause, half the time half way through it goes to down version that is compression glitched and blurry, on and on.
If so much of the site is video, why not make that the slickest player of all time? Youtube has always known how to do this. Streaming services do as well. Open source tools are better than this. What is going on reddit with the video player? It probably has lots to do with tracking, cost savings and more but it is unwieldy right now.