If you're interested I talked to a developer at Mux (they serve billions of video views per month) about their tech stack at https://runninginproduction.com/podcast/31-mux-is-an-api-bas....

Around the 1:14 mark he goes into why you can't just use the html video tag. It was one of the best explanations I've heard around HLS and what it takes to stream video efficiently.