I'll not talk about the platform they provide instead I'll talk about the technical superiority they have which other platforms will have a hard time to reach.
YouTube keeps multiple resolutions of your video. Note that the audio is kept separately from the video which means that if you decide to switch resolution it does not necessarily have to switch the audio too even though the audio is usually also provided in multiple resolutions.
With automatic resolution settings YouTube is able to optimize your video on-the-fly based on the network conditions and if either audio or video is still buffered it can be reused.
There are usually 6 different video and 4 different audio resolutions available.
To watch a video it has to be streamed to your computer. In the web we usually use HTTPS for that.
HTTPS is a protocol build on top of TCP and is therefore reliable so it's made sure that no frame of the video is lost.
But in a video you usually don't care about frames being lost and therefore you'd prefer a protocol that is based on UDP for video. This kind of protocol did already exist for the web before WebRTC and is called QUIC. Is seems to much effort to use QUIC for the average popular video hosting platform but YouTube uses it. Which means that you won't notice packet loss in an acceptable amount.
By the way QUIC uses 0-RTT TLS.
To support browsers every video has to be converted into multiple resolutions with multiple codecs. To do this quickly you need a lot of computing power. YouTube is literally done in no time in regards to the amount of effort that is spend on converting the uploaded video.
Usually 22 seperate files will be created from one video.
A note on browser support
- QUIC is only supported by Chromium-based browsers and Opera as far as I know.
- There're usually not multiple audio "resolutions" available if you use < IE14 or Safari.
- The video is usually around 15% larger in size if you use < IE14 or Safari.
- Audio may not be transferred separately from the video. Probably if you have an old browser (most likely one that has to fallback to flash)
A note on other video platforms
- Some have a couple different resolutions but it's hard to get to where YouTube is with their way of handling this.
- QUIC shouldn't be hard to use but I don't know of any platform apart from YouTube which makes use of it.
- Remember that the video player is hard to implement correctly with all those different codecs, flash fallback, jumping around in time, buffering, etc.