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0 pointsmarta_morena_285y ago0 comments

TCP doesn't take care of packet loss. What TCP does is make sure your packets are not lost, even if you have 99% packet loss. On the flip-side, that means that if TCP can't deliver a single packet (say out of a billion), the whole stream stops at this one packet...

Which is why TCP is a horrible choice for any streaming service and a horrible choice for lossy connections, and I would be quite surprised if Netflix relied on it. UDP is the perfect choice for streaming, since video decoders can handle packet loss pretty well. The rest you can achieve with good tradeoff between Reed-Solomon codes and key framing.

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ReactiveJelly5y ago

I can't find any solid source for it, but I think most web video streams are TCP:

https://news.ycombinator.com/item?id=8638946

Even the live ones like Twitch.

Because they all want to run through HTML5 web browsers, re-use the same TLS as everyone else, and not write a ton of new code.

When QUIC gets big, they'll probably switch to UDP - Not cause it's better on every connection, but because it will be popular and it will be better on lossy connections. But for now TCP does work fine.

That's why youtube-dl can rip video without implementing tons of weird proprietary protocols - It's just HTTPS. Otherwise these video sites wouldn't run at all in Firefox.

alaties5y ago

I'm not sure this statement is generally true for Netflix's use case.

UDP provides no out of order packet handling which _needs_ to be handled for video streaming. UDP is by default unbuffered throughout transport and tends to cause greater stress to client systems since they need to respond per packet rather than per traffic stream (IP+port combo). As a client developer, you end up reimplementing 90-95% of what TCP gives you out of the box at great development and QA cost. You also drain battery on mobile devices with all the interrupts your causing doing UDP. The upside with a UDP-based implementation is the latency from server to client display is usually much less (tens of milliseconds vs hundreds to thousands), but the trade-offs involved are almost never worth it for a static media streaming site like Netflix.

Even dynamic media streaming sites like Twitch rarely dip into UDP server-client implementations unless there are some unusual requirements.

petzen5y ago

You'd only allow packet loss without re-transmission (e.g. pure UDP) if you really need low latency, like for a video call.

Netflix is pure TCP I'm sure - look up HLS and DASH.

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