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Near Video on Demand
If you are anything like me, the one thing you can bank on is that BBC, ITV, Channel 4 and 5 for that matter, will start their feature films at an inconvenient time (to me). For example, Channel 4 features are a lost cause, because my mum told me most severely before I left home that I must be in bed by eleven. I try to use the video but I either forget to program it or it gets lost with all the others that I failed to label! So, if Saturday night viewing looks awful, we call by the video store on the way home from shopping. Thats good, because we can press the play button when we want to.
Now, all this is not lost on broadcasters fighting for every percentage point rating and digital compression offers the tools to fight back ... near-video-on-demand or NVOD for short. The principle is simple. If you've got more channels than you know what to do with, why not use a block of, say, six of them to play the film with staggered start times. That way your viewer is never more that 20 mins away from the start of the film whenever he (or she) sits down. And that is the way you'll see it on Sky Movies or Front Row on cable.
But not, unfortunately, on DTT - alas, poor dears, they don't have enough bandwidth for NVOD. But, maybe I'll be eating my words in a year or two for the following reason. Nowadays, broadcasters don't play their movie channels from banks of videotape machines - they use a computer fileserver which can output several channels from the same file on hard disk store.
Using statistical multiplexing, it is possible to vary the datarate share between channels so that difficult pictures are given more bandwidth instantaneously and easy ones less.
And if, as is the case with NVOD, the file or files are pre-recorded, then it is possible to do some pretty sophisticated (and lengthy) 'robbing Peter to pay Paul' calculations before transmission to achieve acceptable pictures at average datarates as low as 2Mb/sec or even less. We shall see!