Streaming pre-recorded video and streaming realtime video are almost entirely different use cases. Pre-recorded video streaming is, under the hood, really just

Streaming pre-recorded video and streaming realtime video are almost entirely different use cases. Pre-recorded video streaming is, under the hood, really just a high-volume variant of serving up static web pages. You have a few gigabytes of file to send from the server its stored on to the device that wants to play back the video. As this presentation demonstrates that isn't trivial at scale, but the core functionality of sending files over the internet is what it was designed to do from day one. Because you can generally download video across the internet faster than it can be played back its possible to build up a decent sized buffer which allows you to paper over temporary variance in network performance without the customer noticing. Realtime video streaming has two variants. One to many Twitch style video streaming is relatively simple, since you can encode video into files and upload them to a server for people watching to download those files. This is how HLS streaming works, and most of the techniques Netflix use to optimise video delivery can also be applied here at the cost of adding latency between the event being streamed and people consuming it. That latency will often sit at about 30 seconds, and people generally find that acceptable. Skype style realtime video streaming is much harder. You're taking video from one person's camera, and then sending it over the internet to one or more people's device. You can't do any sort of pre-processing on that, or stage the video on servers closer to the consuming users, because you have no way of generating that video until the point your users decide to start talking to each other. Because you can't pre-stage that video you need to be able to establish a network route between the people on a call, potentially in an environment where none of the participants have any open connection from the internet directly to the device they're streaming from. Slight fluctuations in network performance can potentially degrade video delivery to the point of it being unusable. The most common route to deal with that is systems that attempt to establish a direct connection (ideally over a local network) between participants, and if that doesn't work going via relay servers operated by the software provider. These servers provide a single point on the internet all parties can connect to, and then allow passing packets as if they were all on the same network.