Video Download Mode

Sorry, this might get a bit technical. On-demand stream or podcast is the question.

On-demand streaming means that when you want to watch something, you request a stream from the provider and (after a few seconds delay) it starts arriving. Youtube and SeeSaw among others are users of this approach. The problem with streaming is that if the link is not fast enough then the stream will not keep up with the display and the picture will freeze for a few seconds. This was apparent during our recent attempt to watch the Dubai Grand Prix on iPlayer. The limiting factor here is often not the local loop but the network and server constraints. Watching the Grand Prix on iPlayer is very popular and currently causes the biggest peaks in network traffic seen by BT.

Podcasting means that you subscribe to a channel and the latest issue is downloaded to your machine when available. The existing protocol relies on the subscriber checking periodically for updates. Miro is an example of a podcast reciever. Once completely downloaded the video becomes available for you to watch. As the complete file is available locally the picture will not freeze while replay is running. It is also possible to use this technique to provide very high quality video over slow connections; the download time may be longer than the running time length of the video. A disadvantage of podcasting is that users tend to download more than they watch. Sky News provide an update of the headlines 4 times every day, however it is unlikely that the typical subscriber will watch more than one a day. Clearly this increases the overall load on the network.

Given a fast enough link, on demand streaming has the advantage of (almost) immediate provision regardless of whether the video has already been downloaded. The further advantage is that the overall network load is reduced because users only download what they actually watch. With increasing link speed as FTTC is rolled out across the country these look to be winning attributes. The caveat about FTTC has to be whether the capacity of the backhaul network is increased fast enough to keep pace.

In conclusion it seems that on-demand stream is likely to emerge as the winner as link speeds increase. In the meantime podcasting has a role to play in providing good quality video over slower connections. This is good news if you already have a fast broadband connection or are about to get one. It is not so good if you face a long wait for FTTC to be wired on your exchange.

Why have the network providers not considered a point to multipoint 'push' version of podcasting. This would be extremely efficient at offloading the backhaul network and would provide better quality than on demand streaming. It seems obvious to us, but who knows?