Ask HN: What would be involved in building your own YouTube clone?

I don't exactly want to clone youtube. But let's say I wanted to make a website where people can upload videos and others can play them in their browser. What would be actually involved in doing this?

I know quite a bit about backend and devops, but I have to admit I have no idea how to do this, if I was tasked to do this.

Also would this even be possible without flash or third party video players? I know youtube used to have an html5 version, but I can't recall what happened to that.

My question is more on the programming level of what you would use to build the actual video player and the how the video player would connect to the backend.

Not so much an infrastructure question.