Comment by hristov | Hacker News Reader

Comment by hristov | Hacker News Reader

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I have an unrelated question for the Justin TV folks. Do you guys use TCP or UDP for your videos? Do you use multicast?

I have been wondering about this lately. TCP ensures all packets are delivered, but it may cause delays retransmitting packets, so I am not sure it would work with live TV. Also TCP cannot do multicast. Youtube uses TCP (AFAIK) but you tube is usually not live.

UDP does not waste time retransmitting packets but UDP does not guarantee all packets will arrive. Thus, with UDP you may have dropped packets. In the old times you would just use UDP and accept that there will be occasional quality degradations due to dropped packets, but in the old times streaming video and audio over the internet was really bad.

Nowadays the expectations are so high and the video codecs are so complex, few dropped packets could cause noticeable artifacts.

Anyways, sorry for going off on a tangent. I was just curious.

We use TCP because Flash mostly doesn't support UDP.

Thanks for the quick response. That makes sense.

Anyways I did not mean to hijack your thread :). We should talk about how cool Justin TV is.

I really like what you guys are doing with live esports. I am hooked on a couple of the starcraft streams. I wish you were around 10 years ago, I might have realized my dream of being a professional SC player.

People are making a living playing SC2 on our site now, by building a huge viewership. There are more and more older players in the SC2 scene -- you might still have a shot!

As mentioned, they have to use TCP because of Flash.

But as a general rule: the higher the loss and the lower the target latency, the worse TCP is. For higher-latency applications, TCP is typically good enough on any typical connection.

How would you do multicast over the internet? That seems like a disaster/not possible.

There actually is a multicast standard on the internet. It uses UDP. Basically, instead of sending out multiple streams of packets for each viewer you send only one stream and the routers copy the packets into new streams as needed along the way.

http://en.wikipedia.org/wiki/Multicast

I am not sure how often it is used and whether the newer routers still support it even.

I have a huge dream about multicast, but on the public internet, it doesn't happen.

Most of the time it happens on private IP networks (think FiOS TV, Uverse, etc., though i'm not sure if they use it.)

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