Strictly in 3D – bandwidth

I posted a couple of weeks ago about the impending broadcast of Strictly Come Dancing in 3D, and I thought a few readers might be interested to know how it all worked out.

The 3D broadcast on BBC HD was preceded by a screen explaining to viewers how to set their TV to the appropriate ‘side by side’ mode, which should have been fairly simple for most – on the Samsung set I was using, it’s the first option that appeared when I pressed the 3D button on the remote control. And on the whole – at least until my guest sat on the glasses and broke them – it worked pretty well.

But what about bandwidth? Well, I’ve checked the recording sizes and durations for the 2D and 3D broadcasts on Freeview HD, as reported by the Digital Stream box that I’m currently using for HD viewing.

The 3D recording of the results show lasted 1h 4m 19s, and took up 4.5GB of disk space

The 2D recording from BBC One HD lasted 1h 4m 28s, and took up 4.8GB.

The difference in timing is probably a combination of the response time of the recorder, and slight differences between the flags being updated on the two channels; at any rate, nine seconds over an hour is negligible and we can, broadly speaking, consider each recording to be about the same length.

So, that leaves us with 4.5GB for 3D and 4.8GB for 2D, and I think that’s more or less in line with what I’d have expected, though there would need to be a lot more 3D around to be entirely sure.

The bandwidth on Freeview HD is shared between the four channels, and the BBC ones at least are ‘statistically multiplexed’, which means that if one channel is showing fast changing information, compared to something more static on the other, then the channel that needs more bandwidth can get it – think, for example, Match of the Day vs Great Expectations. Match of the Day will very likely get more bandwidth.

But, of course, for Strictly, it was essentially the same programme on two channels, and so the end result was always going to be pretty similar, and for the short to medium term at least, I think it’s pretty much inconceivable that any 3D broadcast won’t also be accompanied by a 2D simulcast, certainly on the BBC.

Why is the 3D broadcast slightly smaller, though? My suspicion here is simply that it will compress a bit better; 3D using the ‘side by side’ format has two almost identical pictures making up each frame – and in doing so, incidentally, halves the horizontal resolution of the 3D picture, compared to the 2D one – and that means more repetition.

Repetition is what compressors look out for, so that they can save space, so my gut feeling – and if you know more about the intricate innards of broadcast compression feel free to comment – is that the side by side format will tend to compress slightly better than a comparable full-frame HD picture.

As to what it looked like? Well, for the bits that I could see, the lovely Harry Judd looked even lovelier in 3D, but like quite a few people, I do find watching 3D a bit wearying, and the standard HD picture was, overall, crisper and a lot easier on the eye.

iPlayer on the TVonics DVRs, IPTV on Freeview

I’ve been meaning to blog about this for a while, since the PR people for TVonics kindly send me one of their DTR-HD500 units to play with (I’ve previously looked at the Z500HD for RegHardware.)

Both units have essentially the same software and UI; the difference with the HD500 is that it’s in a rather more stylish case, which you’ll either appreciate or think “That’s just bonkers!”

TVonics DTR-HD500 - unconventional styling

Both models include a two port HDMI switch, so you can connect a games console and DVD player, for example, as well as the DVR, even if you only have the one HDMI port on your TV; unlikely as it may seem to the more techy amongst us, there are still a lot of people out there who will have a shortage of HDMI ports on older TVs.

I won’t go over the main points of the TVonics kit in too much detail – read my review on RegHardware for that – but it’s a fairly straightforward interface that perhaps verges on the bland, but certainly won’t frighten people who are not used to digital TV.

The latest updates to the products add support for IPTV services, including the BBC iPlayer, thanks to support for the latest D-Book version, including the MHEG Interaction Channel.

That means that, essentially, when you’re watching a BBC channel on Freeview, you can press the red button on the remote, and you’ll get iPlayer as one of the options on the menu.

iPlayer on Freeview HD - just press Red

As you can see, it’s much the same implementation as you’ll get on a Freesat box; easy enough to find your way around with the remote control, but lacking some of the fancier touches found on the dedicated apps used by some manufactuers, like the one on Panasonic’s VieraCast, which I talked about recently over on RegHardware. However, this is what the BBC provides, not TVonics themselves, so it’ll be common across a lot of Freeview HD boxes over the coming months.

That’s not all that’s added by the latest software update, however. If you’ve browsed the upper reaches of the Freeview HD programme guide recently, you’ll have seen that, past the porn section, starting at channel 110, there are several new channels listed.

These are IPTV channels, which work using the MHEG-IC functionality on Freeview HD boxes. You can tune in to them on any box, but you’ll see a screen something like this if you do:

If your receiver doesn't support the IPTV channels, you'll probably see a message a little like this

On the TVonics – assuming it’s connected to the network, which is pretty much plug-and-play using an ethernet cable (a wireless adaptor is also available, but I’ve not had one to play with) – then you’ll see the station logo (‘Sports Tonight’ on channel 112, for instance) followed by message ‘Attempting to start video’ and then the picture will appear.

Sports Tonight, on Freeview channel 112

If I had to describe the picture quality, I’d say “VHS”; it’s hard to know if it could be better or not – certainly my broadband connection is more than fast enough, so the limitations are to do with the channel itself, and how much bandwidth it wants to pay for. Also, in the screenshot above, the programme was doing an interview via Skype, so it’s not exactly a fair example of what’s possible.

Some may, no doubt, be wondering why Freeview bandwidth is being taken up by minority channels, but the good news is that these channels really aren’t having much impact. All that has to be arranged is a slot in the EPG, and a very small amount of data, which essentially just provides the loading screen and the logo. The channel then points to the IPTV stream, if your box understands it, and all the programme content is delivered over the internet.

It’s obviously a lot cheaper for channels to get on air like this, and as more TVs come with Freeview HD and D-Book 6.2.1 support, we can expect to see more of this sort of content, including paid events and subscription services, helping Freeview fight its corner against other TV services.

For those who are curious, there’s a reasonable amount of buffering, it seems – it took five seconds from unplugging the network cable in the back of the TVonics before the channel was affected.

Dolby transcoding for Icecrypt T2400

Owners of the Icecrypt T2400 will be pleased to hear that a new firmware update is being tested at the moment, which will add Dolby digital transcoding to the unit.

In my original review, that was one of the main points against it, so if this works well, it will be very good news for users.

I hope to start testing the update in the next couple of days, and will post more about it next week.

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.

Technology to watch out for: DTCP-IP

I’ve been meaning to explain this acronym for a while, and a recent announcement from the DLNA (who create some of the standards that are supposed to make home streaming simpler) is probably as good a reason as any.

Regular readers will recall that I’ve seen various recorders over recent months that have fairly advanced functionality, allowing you to record programmes on the hard disk and then watch it over the home network, and predicted we’ll see more of them.

For example, last year’s Panasonic FreeviewHD recorder could do the trick, and it’s due to come to the Humax FreeviewHD boxes too. But, right now, it’s a little limited, because of content control issues – that’s the rules that say, for instance, that some material broadcast on FreeviewHD can only be copied to disc once.

Now, I know that to some, the very idea of content controls is horrific, but I think for now at least we have to accept that they’re here, and take organisations like the BBC at their word when they say that without them, they probably wouldn’t be able to broadcast some of the material from big Hollywood studios in HD, unencrypted. Whether that’s really the case is an argument for another day; for now, we have to live with this technology.

Streaming content

One of the consequences of content controls is that it can make home streaming fiddly (and, to be frank, DLNA can be quirky at best of times, as it is). With the Panasonic recorder I looked at last summer, for example, I could access both SD and HD content remotely on a 2010 Panasonic TV set, but I couldn’t access anything at all on my 2009 Panasonic; a Sony set with DLNA support could access only the SD material from the recorder.

At a Humax presentation where in-home streaming was discussed, we were told that, initially at least, streaming would be from the Humax recorders to other Humax set top boxes.

Essentially, a bit like the early days of WiFi, if you want a painless experience making it all work together, and all your TV programmes available to watch on any set, you’re best to stick to one brand. Go with a Panasonic recorder, and make sure you have recent Panasonic TVs on which to watch over the network. Or go with a Humax recorder, and put one of their set top boxes underneath each telly.

If you’re starting from scratch, that’s simple enough, but of course many of us aren’t, and we can’t afford to replace everything.

Why does this happen? It’s because of those content controls; if a programme is protected so that it can only be copied to disc once, or perhaps isn’t supposed to be copied at all, sending it over the home network to a random device about which you know nothing is not exactly within the spirit of things, is it? That other device could be a PC with software to record the stream, for instance, or a disc recorder.

Introducing DTCP-IP

And this is where DTCP-IP comes in; it’s a mechanism by which devices on a network can establish a secured connection with each other (a bit like using SSL for a browser) and use that connection to transfer not just the content, but also the information about how it has to be protected, such as whether it can be saved, or sent to an analogue output, and so on.

You might think from the name that it’s something to do with the TCP/IP networking protocol, but that’s not wholly accurate; the DTCP part actually stands for Digital Transmission Content Protection, which is the basic encryption and control system. It can be used over a variety of connections, including FireWire, but what we’re interested in here is DTCP-IP, and in this case the IP stands for Internet Protocol.

In other words, DTCP-IP is the variant of the Digital Transmission Content Protection system that works over the internet and home networks. It’s licensed to manufacturers by a group called the DTLA, and the major backers of the standard including Panasonic, Sony and Toshiba.

In late May, the DLNA issued some new guidelines which included the use of DTCP-IP (and much overuse of the word ‘leverage’, but I digress). This will hopefully mean that more manufacturers will include the technology in their products.

What does that mean?

In theory, if DTCP-IP becomes more widespread in devices that can access your home network, such as TVs and media players, as long as those devices that can share it also step up to the plate, then instead of having to stick with a single vendor to ensure compatibility, you’ll be able to pick and choose your equipment, and know that even if you have a Sony TV in the bedroom and a Panasonic recorder in the living room, you’ll be able to watch recorded shows in bed, without any problems, including those in high definition.

There are almost certainly bound to be teething problems; as many people pointed out when RegHardware looked in more detail at DLNA, if two boxes say ‘DLNA certified’ on them, there’s still no real guarantee that one will play content from the other, and right now a lot of consumers could be forgiven for thinking that DLNA certification is a bit of a mess.

If that can be sorted out, however – which means specifying which file formats players and servers should handle – then DTCP-IP will make it simpler to pick the kit you want for home streaming. And potentially, it’s not just streaming from your home recorder to your TV that’s involved here. It can be used over the wider internet too, and that could make it easier for online movie services to be available on a bigger range of streamers – instead of having to restrict, say, LoveFilm to boxes that have done a deal and had their software tested for security, they could be available to any that support DTCP-IP.

DTCP-IP is also – as far as broadcasters and content owners are concerned – a crucial component of the long mooted move to ‘home gateways,’ where a single multi-tuner receiver somewhere in the house is the only thing connected to the cable, satellite, or internet feed, with all the content available on any screen in the home.

One to watch

So, you might not have heard of it yet – and it’s probably unlikely that you’ll see stickers on boxes proudly proclaiming ‘Supports DTCP-IP’ – but I think this is a technology to watch out for, especially if you want to make the most of your home network, and watch your recorded TV wherever you like.

TVonics DTR-Z500HD review update

As I mentioned in my recent piece on choosing a Freeview HD recorder, I’ve been playing with the TVonics DTR-Z500HD; I omitted to update it with the link to my review on RegHardware though.

I confess to one mistake in the review – corrected in the comments – which was not originally noticing the EPG genre browse/search functionality. In fairness, this is partly the way things are labelled on screen, with the colour keys used for some functions, and the |<< and >>| icons at bottom left and bottom right not labelled. It isn’t immediately clear that these provide access to an extra screen of functions for the colour keys, which includes the search option. Still, I shouldn’t have made the mistake, so many apologies.

The TVonics EPG does have search - but it's not immediately obvious where to find it

I think the photo shows the problem – on the left, a quick glance may make you think the |<< button is actually PgUp, and on the right >>| isn’t labelled at all. Perhaps ‘More…’ would be a suitable label.

On the whole, I think the TVonics has a pretty reasonable interface, it’s pretty straightforward, though a little on the sparse side. Mostly that works well, and means menus don’t look too scary, but it sometimes has its downside. For another example, here’s the screen when you set a recording:

Setting a timer on the TVonics

The screen gives you all the information you need, without clutter, but that grey box always covers the whole of the centre of the screen, with options below, right at the bottom. Personally, I think that large space makes things less obvious; while there’s a reminder to press Blue for Series, the Red button for HD is tucked away in the corner.

I know there are design reasons for always having that box the same size, regardless of the name of the programme, but I think from a usability point of view, I’d prefer to see it shrunk to fit, with the colour keys indicated clearly, right below the message about the recording being set.

Of course, once you’ve been using the box for a while, this sort of thing will become second nature, just like on other boxes I’ve learned to press the Record button, then down to select series, and tricks like that. But for the casual user, or someone just coming to a box fresh, it can make it a little less straightforward.

A good performer

None of this is to detract, however, from the fact that the TVonics is a pretty good box; it’s an affordable price, has the all-important Dolby Digital output – and a fix for a bug I found in that while testing appeared very quickly from the guys at TVonics – and isn’t so laden with extra features and complexity that it will confuse the less tech-savvy members of the family.

I still wish it had folders for organising recordings though…

I’ve just written up a review for Computeractive, by the way, which should be published soon.

Q&A: Digital audio formats

Time for another question, from Paul Hunter, who asks

“what is the difference between PCM 2.0 stereo channel and Dolby Digital (DD) 2.0?  I have a brand new amp (Onkyo) which shows that Standard Definition  TV programmes, via my Humax HDR Fox T2 recorder, are transmitted in PCM 2.0, whereas the majority of HD programmes are transmitted in DD 2.0 (although some in DD 5.1).  My amp appears to be capable of converting both the PCM 2.0 and DD 2.0 input formats to 2.1 stereo, or even 5.1 surround outputs.   Please could you explain the difference between PCM 2.0 and DD 2.0 inputs?”

There’s not a massive difference, in terms of what you’ll hear, really. The 2.0 indicates that the signal has just two channels of audio, and no separate channel for the subwoofer. When your amp converts this to 2.1 what it’s really doing is filtering off the low frequencies and directing them to the subwoofer channel.

But stepping back a bit, the real question – what’s the difference between PCM 2.0 an Dolby Digital 2.0, given that they are both stereo signals?

PCM stands for Pulse Code Modulation, which is a pretty simple way of encoding digital audio, without compression. It’s understood by just about every bit of AV kit out there, and you could call it the lingua franca of digital audio, I suppose.

Dolby Digital is a codec, which involves some compression, so theoretically if you were to take the same audio signal and encode it in PCM and Dolby Digital, you might (depending on the bit rates involved) hear a small difference, in favour of PCM.

Both formats can be used for stereo or multi-channel audio, however because of the uncompressed nature of PCM, you can’t really get more than two channels down an S/PDIF link, whether optical or digital, though some kit will support multi-channel PCM via HDMI. But I digress. Back to the 2.0 versions of each:

On Standard Definition Freeview (and most other services) the soundtrack uses MP2 compression. Some kit will support that, but not all, and when you’re using a digital connection, whether HDMI or S/PDIF, the most straightforward thing to do is simply to decode it to PCM audio, and so you get a PCM 2.0 stream from your receiver.

On High Definition channels on Freeview, the sound uses the AAC codec (and can use HE-AAC, which is the High Efficiency version of the same codec). This is used for both stereo and multi-channel programmes, and like the MP2 audio on standard def channels, can be converted to PCM.

However, not all home AV kit has HDMI, so many people will be relying on an S/PDIF connection for their audio. And some kit with HDMI doesn’t support multi-channel PCM, either.

So, for surround broadcasts, the most sensible thing to do for broadest compatibility is to convert the AAC multi-channel audio into Dolby Digital 5.1, and the chipsets in many FreeviewHD products are capable of doing this. Kit connected via HDMI can tell the receiver if it will support multi-channel PCM, but via S/PDIF that’s not possible, as it’s a one way connection. So, creating Dolby Digital is a solution that will work for most kit, and will work whether the programme is in stereo or multi-channel audio.

It would be possible to switch between using Dolby Digital 5.1 and PCM 2.0 when a programme is broadcast in stereo on HD channels, but that’s not generally considered a great idea. Lots of kit will handle it perfectly, but some won’t, and you may get a momentary loss of sound, or some other audible glitch. So, it’s best to stick to the same codec, and simply indicate the number of channels included in the stream.

This is less of a problem when changing between SD and HD channels, of course, because you’ll be expecting to lose sound and vision anyway.

The quick answer to the question, then, is that it’s just a different codec, but the signal is still in stereo. And the details, above, explain why it makes sense to create a Dolby signal even for a stereo programme.