BBC details of the Streetdance 3D broadcast

Regular readers will recall that at the start of the month, I wrote about the broadcast of Streetdance 3D on the BBC HD channel, and speculated about the method that was being used to provide support for 2D viewers.

In a blog post today, Ant Miller at BBC R&D reveals how it was done.

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.

Wimbledon goes 3D

The Mens’ and Ladies’ Finals of this year’s Wimbledon Championships will be the UK’s first free to air 3D television broadcasts.

The BBC has announced that live 3D coverage of the finals will be provided on Saturday 2nd and Sunday 3rd July, on all the digital TV platforms that carry the BBC HD services. The finals will be broadcast in standard definition on BBC One, in high definition on BBC One HD, and in 3D on the BBC HD channel.

There will also be live 3D screenings in some cinemas around the UK, and I daresay a lot of shopping centres will be getting in extra sets of specs, in the hope of shifting plenty of kit on the day.

The BBC press release puts this firmly in the “editorial experiment” category, so it’s premature to expect any regular service at the moment; this is a test, and also a way to mark the 125th anniversary of the Championships as well.

How it works

The release is a bit short on the technical detail, about which I’ll see if I can find more information (Update: ‘side by side’ format is confirmed; see below). But since no special receivers are required, then my gut feeling is that they’ll be using the ‘side by side’ format to broadcast.

In ‘side by side’ 3D, a single frame actually has two images encoded in it, one for the left and one for the right eye. So it looks a bit weird to an ordinary receiver, but you can still make sense of it, as it’s just a picture, albeit with each half almost the same. A 3D TV, however, will spot the format and zoom each half to full screen, and ensure the left image goes to the left eye and the right image to the right eye, via whatever 3D screen technology it actually uses. The downside is that horizontally, instead of 1920 (or 1440) pixels, since there are two images, each eye only receives half that resolution.

It’s possible to broadcast in other ways, but unlikely, I think.

For example, ‘frame sequential’ 3D requires sending a full HD frame for the left eye, and then one for the right eye. This is Panasonic’s preferred format, because each frame is full HD resolution, but of course that means a lot more bandwidth; you at least have to double the frame rate as you need twice as many images. I suspect, at rates that a receiver understands, this wouldn’t actually break most 2D sets, but you’d get a nasty flickering. It’s really best suited to delivery systems like Blu-Ray.

And, since Freeview HD can only go up to 25p as a frame rate, it’s not possible to use frame sequential, on that platform anyway – you’d effectively be getting only 12.5 frames per second. And I think it’s unlikely the BBC will be using different 3D formats for different platforms, too.

The other way of sending 3D, ‘2D plus depth’ is, unless I’m a bit behind, not an entirely finished standard; it involves sending information about the details for one eye, plus that needed to make the image for the other. Ultimately, some variation of this may be used to create a ‘service compatible’ standard, which is one where someone with a 2D set can tune in and see a decent 2D picture, while a person with a 3D one will see the extra dimension – which will avoid the need to have a separate broadcast stream, as the BBC are doing this year.

So, based on what I know now, I’d say it’s most likely going to be a side by side broadcast; I’ll try to check this when I can, though there wasn’t time between reading the release and the end of the embargo.

Definitely a worthy experiment, I think, and it’ll be interesting to see what people make of it. And how many people moan that three channels were taken up with the same programme.

Update: This BBC blog post confirms that they will indeed be using the side by side format, and increasing the resolution of the stream to the full 1920 pixels.

BBC One HD launches 3rd November, BBC HD changes channel no

The BBC has confirmed that BBC One HD will launch at 7pm on Wednesday 3rd November, across all the digital TV services where the current BBC HD channel is available.

You’ll find the new channel – which will be a simultaneous broadcast of the main BBC One – at Freeview channel 50, Freesat 108, Sky channel 143 and Virgin Media channel 108.

The exisiting BBC HD channel will move to Freeview channel 54, Freesat 109, Sky channel 169, and Virgin Media channel 187.

Eastenders in HD? Not yet!

While the recent burning of the Queen Vic in EastEnders has heralded a new set, ready for HD production, the show won’t actually be in HD until Christmas Day, according to the BBC. So while you’ll get to see the new Vic next week, you won’t see it in all its glory until then.

Wednesday the 3rd will see a raft of programming in HD, starting with The One Show, followed by Wallace and Gromit: World of Inventions. Programmes that aren’t yet made in HD will be upscaled.

The existing BBC HD channel will showcase the best HD material from the BBC’s other TV channels.

Gone Digital’s original announcement is here.

Update: Here’s some comment from the head of BBC HD, regarding the launch.

BBC ONE HD - The Apprentice, part of the launch night line-up. Thanks to the BBC for this image