How To Start An HD Channel From Scratch
It's been a mad mad time for High Definition TV over the last two years!
At the start of May 2006, there was no UK HD and by the World Cup two months later, BSkyB and BBC HD channels were up and running. Now there are 18 HD channels in the UK, with Freesat offering two free-to-air HD Channels with no need for a subscription.
Now I think the time is right to talk about the history of the BBC HD channel (technically, that is) by winding back to 2005 and sharing some of the stories of the unsung heroes who put together the technology. For anyone who wants to know more about the nuts and bolts of the HD standards have a look at the EBU document Tech 329E. I can recommend it as bedtime reading!
At the end of 2005, the BBC had just announced its intention to run an HD trial on the three broadcast platforms which was an interesting technical challenge to say the least. Sky was working on its HD satellite set-top box and Virgin had its V+ box option, but for digital terrestrial we had to start from scratch. DTT spectrum is very tight and a national trial was out of the question, but we did manage to negotiate permission to use one of the channels reserved for use after analogue switchoff in the London area from the Crystal Palace transmitter. The BBC HD channel was allowed to use channel 31 that sits between the C4 and BBC2 analogue services. It had to use relatively low power and it was monitored carefully to make sure there was no interference.
So, now we had the ability to transmit HD - but what was going to receive it?
There weren't really any off-the-shelf HD terrestrial set-top boxes around that we could use if HD was ever going to be possible on DTT. Conversations were started with all the key manufactures to see if they could develop a prototype box and deliver the number we needed for a very limited trial - and do it in the six months before the World Cup.
I can only image the conversations John Zubrzycki (BBC Research) had with set-top box manufactures in late December:
John: We are going to do a trial of HD on digital terrestrial and need to develop a set top box.
Manufacturer: Great, we can get our development team across it. What's your timescale and how many units do you need?
John: Well... it would be good to have. say. 500 for a trial in June.
Manufacturer: June, that's June 2008?
John: No, this June - in time for the World Cup.
That was probably followed by the sound of the phone going down!
Picture: Richard Salmon testing set top boxes and televisions
However, two manufactures rose to the challenge and by May, BBC R&D Kingswood Warren was overrun with HD boxes and televisions being tested. Richard Salmon reckons he watched nearly a week's worth of television and test signals every time there was a software update - and there were many, many updates.
The boxes were finally delivered to the trial participants in time for kickoff of the World Cup.
Picture: Just a few of the HD Ready TVs under test!
Picture: The Humax and ADB Terrestrial HD set-top boxes under test
Moving on to programmes, one of my jobs before we had an HD service was to help production teams deliver their programmes in HD to some of our major co-producers. Very early on, we discovered that no-one would accept Super 16mm film as an HD format. I did a lot of work with post-production facilities to try to come up with a way to make it possible, but there was no compromise: Super 16 was just not HD.
So when our own channel came up, I thought we should have another go. After all, we would be using MPEG4 not MPEG2 (like our US co-producers), we would have a high enough bit rate and we could look at drama as well as documentaries.
I think I spent two solid weeks looking at different trials, transfer routes and transmission simulations before I had to tell Seetha Kumar (Head HDTV) that about 25% of the programmes we thought we could transmit couldn't be called HD. The problem was that the MPEG4 transmission system did a very good job of removing all the grain from the film but after that the picture looked soft and there was no way we could call them high definition. It was a tough time and we are still working on the problem.
Still, the HD Channel would have the World Cup and Wimbledon to open, followed closely by the Proms - and though they were themselves major challenges, if we could get the pictures back, they would be a great launch for HD.
That brings me to the engineering planning for Wimbledon (2006). We could not cover the whole Wimbledon site in HD but we could do Centre and No.1 courts - and, even better, we could do it with surround sound. Everything was going well until we discovered that the fibre which carried the 100Mbs link from site back to Television Centre popped up in a room on the wrong side of a wall! There was plenty of standard definition connectivity between the room and the main switching matrix - but no HD.
Someone suggested that we could down convert the pictures to standard definition and route them through the up convert for transmission - I'm not sure what his job is now! The discussion went round and round for a while trying to resolve the problem until the OB Engineering Manager suggested their solution would be a power drill and a large hammer! I'm not sure that everyone around the table appreciated it, but it did focus minds to come up with a reasonable solution!
The guys in the central apparatus area are always innovative when it comes to providing a quick and temporary solution. I found out exactly what "quick and temporary" meant when I went to see the first test pictures arriving from the World Cup site. All the original World Cup planning had been done when there were no thought of HD transmission and everyone had worked incredibly hard to move the whole operation to HD.
For the BBC coverage, this was made more complex because we had the main studio in Berlin while the International Broadcast Centre (IBC) was in Munich. The first shot we saw was a rather stunning view of the Brandenburg Gate through the glass wall of the studio and it was really good to see everything working. After a while, I was shown some of the equipment recently installed to route HD to Red Bee for transmission and, as you would expect, it was all neat and shiny with plenty of blue lights - except when I asked what the rather dirty video cable hanging from the ceiling was for. I was told it was the main (and at that time only) HD feed coming in from Germany. I wished I hadn't asked.
So, other than the "odd" bit of routing, all seemed well three days before the World Cup: the channel had launched and the promo loop was playing and getting a big audience! I had even managed to get away early on a sunny afternoon, then I had a call from an old editing colleague - "did you know your channel was out of sync and it looks like it looks like it's getting worse?".
Okay - don't panic - just call Red Bee to see what's happening.
They checked and told me that all seemed fine but that they would keep an eye. I trusted my source and needed to know more and as my Sky HD box had arrived the day before and I spent the evening watching the promo as it cycled and yes, by about 10pm it was defiantly out of sync.
The next morning it was still out when I checked just before I left for work. The previous night, I had e-mailed Seetha to say that we may have a problem - I could just imagine her reaction when Gary Lineker started to speak at the opening of the World Cup and a second or so later his mouth moved.
The more we checked the more confusing it got. The promo was definitely in sync on the original tape and on the server original server file and there was no point in the chain that could put the signal out of sync. We needed to see some live pictures through the chain and they needed to see sync on and we needed to do it quickly. So for all those people who contacted the BBC audience helpline (and me), the reason the London news went out on the HD channel in two short bursts one afternoon was so that three guys at Kingswood Warren could stare at the newsreader's mouth!
To the relief of everyone, the news was in sync - so the footie was safe.
But that didn't explain why the promo was going out over a period of time, would it do the same when we started transmitting real programmes from the server? Mike Taylor from Red Bee did some sterling work and tracked it to an "oddity" in the playout software. It's quite unusual to play out a programme again and again (and again and again) from a broadcast server and after a few days a very small error had built up, enough to see. Simple to fix once you knew what it was - but for 24 hours it wasn't an experience I want to have again!
Two days later, the World Cup kicked off and then the "fun" really started...
Andy Quested is Principal Technologist, BBC Future Media & Technology.