On-demand video streaming

Question

I'm currently researching different streaming methods both for live and on-demand streaming.

I've read about both multicast and unicast, and now I got the following question, which I can not find an answer to.

"Is it possible to make on-demand streaming with multicast?"

The way I understand it is, that when using multicast, the media server creates a stream of the video, which only is played once, which users can connect to and watch.

It it because multicast only allows live streaming? If not can someone please explain to me how it works?

Answer 1

"Is it possible to make on-demand streaming with multicast?"

Technically, yes. Practically, no.

The way I understand it is, that when using multicast, the media server creates a stream of the video, which only is played once, which users can connect to and watch.

You understand it correctly. And that is that.

Answer 2

Yes, it can be done, but there are caveats. If you take a flight on an old plane you may see an old entertainment system that offers say 20 channels with a movie on each. The channels are all rolling and once the programmes have finished they restart. This is better than having just one channel broadcast on a projector as it gives the user choice of what to watch but doesn't give them the freedom of when to watch.

Modern flight entertainment systems are all on-demand, every passenger can watch any film at any time. So how can multicast help there is the question? If you detect that multiple users are watching the same film, and the caveat being at the same time, you can replace the streams to each user with just one multicast channel. Which is technically savvy but you have to ask why would you do this? This only makes sense if the communication medium is feeliable or insufficient to serve every user simultaneously.

Designing a flight entertainment system that does not scale to every passenger actually using it is a bit short sighted. Therefore the system can handle the worst case of a stream for each user, meaning there is no benefit for multicasting anything.

Some cable/satellite networks implement multicast streaming and use time windows to group as many viewers together as possible. For example wait up to 5 minutes to watch a video whilst displaying the infamous phrase "buffering".

Answer 3

Well, you can do it, but the bigger question is why would you want it?

On-demand suggests that you start the broadcast at the time that a single viewer wants to see that particular piece of content. If a single user chooses the content and the time it is started, why would you want to multicast it?