More 3D on BBC HD – Streetdance

If you thought that the final of Strictly Come Dancing in 3D was all you were going to get from the BBC over the holidays, you might have missed an unexpected treat on New Year’s Day, in the form of Streetdance 3D, on the BBC HD channel.

I watched this mostly because it features dance dreamboat Richard Winsor, whom I’ve seen several times at Sadler’s Wells, but also because I was a little curious about it being broadcast in 3D. It was only a few days ago I posted here that it would be inconceivable that 3D broadcasts wouldn’t, for the time being at least, be accompanied by a 2D simulcast for those without a 3D set. Yet the film was scheduled only on the BBC HD channel, so what was happening?

The clue, it turned out, was in the red button. Switching to the channel while the film was on showed the familiar double image of a side-by-side HD broadcast, where the picture is split down the middle, with an image for each eye on one side of the screen.

Repeated on each side was a red button icon labelled ‘Watch in 2D’, and pressing that switched to the 2D version. So far, nothing unusual there. And my first thought was that it was a simulcast, perhaps using one of the interactive streams that wasn’t needed for anything else.

Except that the 2D version looked better quality than standard definition, and I don’t think there’d be the capacity, even on a day when there’s no sports, to manage that. Another give-away was that there wasn’t any break in either picture or sound when switching between the two. Normally, if the box has to tune to another stream, there’ll be at least a momentary break in both.

Technical tricks

So, how was it done? My guess – I’m waiting for the BBC to confirm, but I’m 99% certain – is that it was all done with MHEG, the interactive ‘red button’ service. This was evident when the application was still available during the following programme.

Pressing Red simply turned on or off one of the useful features that MHEG provides, which is video scaling. Taking advantage of the side-by-side format, the application simply took the left side of the screen, and zoomed it to fill the whole screen; obviously there’s a small loss of horizontal resolution in doing that, compared to broadcasting a full screen HD picture, but it still looked better than SD, and meant there was no glitch on switching formats.

How do I know it was the left hand side? ‘A little Later’ was on after the film, and the application was still live for at least a part of that, with the icon appearing twice on screen. Pressing Red during that zoomed the left side of the screen, losing the right.

So, I’d say that on the evidence so far, it looks like it’s perfectly possible to provide a 2D/3D simulcast without using any extra bandwidth. The downsides are that resolution isn’t quite as high as for HD, and 2D viewers have to take a positive action to see the ‘normal’ version, unlike the Strictly simulcast, where they just tuned to a 2D version.

You probably wouldn’t want to use this for a BBC One programme, because it would end up on the standard def channel version of the channel (unless that can be fed separately from the HD version), and a lot of older set top boxes don’t have an up to date MHEG engine which can handle the video scaling, so wouldn’t be able to switch to 2D; all HD boxes should have the necessary software, as long as they are FreeviewHD certified.

Incompatible equipment

That means, incidentally, that users of the 3View box probably wouldn’t have been able to select 2D, as it doesn’t have MHEG built in, and the same would be true of people watching with a generic satellite receiver, rather than a Sky or Freesat branded one.

So, this is also potentially interesting from that point of view; whatever equipment you have, even a generic satellite or HD terrestrial tuner, you would have been able to watch in 3D. But only equipment compliant with one of the UK’s platforms – FreeviewHD, Freesat or Sky – would have given 2D viewers the opportunity to select that version of the broadcast.

This sort of thing is not going to happen very often, but nevertheless it raises interesting questions about exactly what equipment should be supported by the BBC, and might well be seen by some as pushing people towards platform-compliant equipment.

2 thoughts on “More 3D on BBC HD – Streetdance

  1. There is a description in the DVB-3DTV specification for doing this stretch without MHEG using MPEG-4 AVC’s cropping flags. However, this will almost certainly need to be tested on a wide range of boxes and require software updates for some before using it.

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