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How video stream relay works or we are building our own CDN

To make a satellite signal receiver and signal transcoder in a format understandable to flash player - this is still not enough, because we have to study to relay video stream. As a rule, all broadcasting systems are constructed in such a way that one part of the system deals with reception and signal coding, and other part deals with it’s relay. Similarly did I, with one exception – I combined relay and transcoder. I.e. if you have a small number of viewers, you can send a stream to them directly from the same server, which is transcoding. And this does not affect performance, because transcoding is realized by certain program threads, and http server is working in asynchronous way. I.e. I have built broadcasting http part in a modular principle and it has no difference, from where to get data for broadcasting - from the transcoding satellite signal module or from another relay.

However, one pitfall is waiting for us here. As I have discussed in the note “Technology of adaptive HTTP streaming from Adobe”, flash player during video stream playing consistently requests server fragments’ files, with time interval equal to duration of these fragments. If to build relay on the same principle, i.e. the relay will send a request to broadcaster periodically, and broadcaster, upon this request, will give a data, then each relay will make a delay. With increase of number of relays, total delay will increase as well, that is not good. So here we will need to swap the server with the client. Relay will be constantly expecting data receipt, and, as soon as the data will be ready, broadcaster immediately will send it to the relay. In this case, the delay will be determined only by time of physical data transfer across the network.

This is how I built the system. Thus, now it doesn't matter, how many relays we will use and by what routes the data will follow between them. The data will appear on all relays with its readiness on the broadcaster simultaneously. Also this fact opens great opportunities to organize our own CDN for video stream delivery, with the rules of work, which can only be taken into head. Besides, our ready-built system opens all opportunities for building peer-to-peer television. This issue I discuss in the next note - Does peer-to-peer television has the future?

Igor, October 2012.

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