If you have ever watched the inlaid videos in the BBCi service, as shown below, have you ever wondered how the images got there? And have you ever wondered how come Sky News' videos could be full-screen but BBC's couldn't?
A little bit of experimentation is called for.
The first thing we need to do is scan through the BBC transponders.
After some delving around, I stumbled across the transponder shown above.
The tuning has changed from that shown. At this time (November 2006), you will want to tune to 11954 H 27500 2/3; the transport stream will say 07dd.
The channels we are interested in are T4 STRM-0 and T4 STRM-1. Select these and add them.
Go to Services and Other channels and choose T4 STRM-0...
Let's see this bigger...
What BBC has done here is actually pretty damn clever. There are two 'channels' (the other is T4 STRM-1) which carry six audio channels and the frame split into six. When you choose a video to watch, the Digibox is directed to take one part of the screen and show it in the box, discarding the rest (it would be masked out by the interactive service background and/or content).
Sky's method looks much the same, but since they use separate channels they can make it full-screen. Actually, it appears that Sky broadcast two feeds on each 'channel', they are full height and half width - when called full-screen the width is stretched out to the width of the screen. So eight feeds (four channels) and the mosaic, Sky's service requires five channels.
On the other hand, careful masking in the interactive service means that the BBC can use the actual content channel as the mosaic. And the BBC can offer twelve different feeds with only two channels. Rather a stroke of genius, no?
There is only one itty-bitty flaw with the BBC service. It cannot be made full-screen (which is a shame, as things like weather maps would be really useful in full-screen). Below is what happens if you take a screen section and try to full-screen it...
If you look around you'll see numerous other channels, such as T4 DEV-# and ETV#. These, as far as I am aware, are intended for use by additional 'interactive' services. For example, the Live8 broadcast - within BBCi - offered a choice of which concert (from those around the world) that you would like to view. After the Christmas Doctor Who, viewers with an interactive box (terrestrial or satellite) could play a game in which they helped the new Doctor save the earth - your choices in the various tests selected which response you were shown.
<cliché>At the end of the day...</cliché> It is six of one, half a dozen of the other. The BBCi mosaic options cannot be brought full-screen, Sky News' can. On the other hand, as needs dictate, the BBC has six or so channels available for providing additional content full-screen. Sky News can't do that!
So perhaps it isn't so bad that the weather forecast is an itty-bitty picture. Because, from time to time, you can watch a selection of other programming. Now all we need is to get the BBC to put, somewhere, a schedule of what they plan to broadcast in this way!