GET OFF YOUR SOAP BOX!

So why have the BBC decided to reduce the bitrate of the BBC HD? Well, trying to squeeze more out of less is linked to HD becoming available on Freeview from 2010. There is simply not enough space to fit in four HD channels on Freeview without sacrificing video and audio quality. Instead on striving for the best digital TV we, here in the UK, will end up with the existing poor quality standard definition and diluted High Definition. You can cut the cake in as many ways as you like but the Freeview cake isn’t big enough. Of course, there is also the issue of the amount of space on Astra satellite and how this space is carved up between broadcasters and then between the channels.

So the introduction of new encoders and the current BBC HD bitrate of 9Mbps is a direct result, and indeed a fine example, of debasing quality for quantity. The BBC HD Blog has a fine post by fireyab9. I have copied it below because, although very detailed and lengthy, captures my layman’s view but with a lot more detail. Have a read.

And it’s not just the BBC Trust or the wealth of executives below them who are letting us down here. OFCOM are accountable for the lamentable mismanagement of Digital Terrestrial Television. They have given the Broadcasters so little to play with. The whole industry seems to be structured around short sighted planning with no foresight or desire to deliver the ‘best’. Instead a typical british mediocre service. SKY’s HD service has demonstrated what a commercially orientated body can deliver to the customer. Not the sort of thing our public servants seem very good at!

So why did we all buy those HD Ready televisions?

fireyab9’s BBC HD blog post…

767. At  on 25 Oct 2009, fireyab9 wrote:

Right here goes. I’ve been lurking here for weeks but now that Paul’s documents are available I really can’t not comment any longer. First of all, I’m not in the profession, but nor am I some “noob” when it comes to MPEG2/MPEG4 video compression, and I know exactly what bandwidth starvation looks like. For the past several weeks, BBC-HD has been a combination of : 1. Massive blocking / smearing artefacts upon movement, 2. Increased halo / ringing artefacts on sharp edges, and 3. Sporadically looking like someone is running the footage through a light pre-encoding softening filter to try and make it easier to encode to hide 1 & 2 artefacts but at the expense of ending up just looking blurry and destroying the prime advantage of higher spatial resolution in the first place. The fact that a Canon *STILLS* (non-camcorder, just a £900 SLR camera in video mode) can produce sharper clearer footage at a lower resolution vs the flagship product of the UK’s (arguably) prime broadcaster is utterly appalling. If I were responsible for that, I’d feel embarrassed to go to work as a professional broadcaster without the intention of fixing it rather than engage in another round of “pass the political parcel” mixed with a Public Relations strategy that can accurately be described as the same “perpetual caring indifference” as years worth of complaints of the “metallic underwater telephone” digital “quality” of DAB have clearly demonstrated.

To me the crux of the whole argument and the oft near deafening silence to the +1,000 complaints spread over 2 blogs have been fully explained in the following two of the “disclosure 1″ document:-

“It will be possible to launch a fourth HD service from mid-2010, for which slot Ofcom has received two applications – one from Five and the other jointly from Channel 4 and S4C”, Sec 1.1

“From the end of switchover, which broadly coincides with the time when we expect the mux to be able to carry five HD services…”, Sec 1.2

First of all the above two sentences are an admission by the BBC that they fully intend to force between 4-5 HD channels onto one transponder. Given that DVB-T2 provides at best approx 36Mb/s (over 24Mb/s of DVB-T), and allowing approx 0.5Mb/s per channel for audio, subtitles, other light data overhead, etc, the BBC basically admits above that their long term goal is to lower the bitrate of BBC-HD even further down to an average 6.7Mb/s per channel… If I’m wrong then please explain with maths (not fuzzy wuzzy PR attempted copouts) how else can you squeeze “5 HD services” into a single 36Mb/s mux. You cannot. Even with “only” 4 channels, it still works out to around 8.5Mb/s video bitrate per chan (another 15% quality drop on top of the already disastrous picture). UK HDTV is fast heading the way of “White Elephant” DAB with exactly the same “bait & switch” strategy of high teaser demo rates followed by a permanent “race to the bottom” sub 3rd world bitrates as soon as take-up starts.

The time has long passed for a much need dose of honesty. I’m very well aware than bitrates can be lowered without quality drop as encoders improve, but there are realistic limits, and claiming to reduce them by 2/3rds without losing quality certainly is to put it bluntly “snake oil” that lies in the same realm as those infamous £2,000 mains power cables for audiophiles… The first SD MPEG2 test broadcasts were around 7Mb/s – they looked awesome. As MPEG2 encoders improved, the bitrates could be lowered to 4-5Mb/s and still look terrific. But anyone who claims the current 544×576 2-3Mb/s Freeview rates look as good is just plain lying. They look awful, riddled with blocks, smearing, ringing and “more blocks than lego” cross-fades. Same with MP3 – the latest tuned LAME codec at 128kb/s can easily match original 192kb/s Fraunhofer codecs, but anyone who claims a new wonder BBC MP3 encoder at 64kb/s can match it would get laughed at – especially on hydrogenaudio (a professional psychoacoustic community who rigorously double-blind test everything without bias or corporate politics). Same with MP2 audio (used for DTT/DSAT & DAB broadcasting) – 192kb/s on newer codecs can match 256kb/s older ones, but the 128kb/s typical of DAB cannot – and everyone can hear the squelchy / metallic / watery / “boiling mud” / pre-echo artefacts, and everyone knows it is simply not good enough and worse than analog FM.

The above paragraph may sound off-topic, but my point is : bitrate drops through improved coding efficiencies do happen, but with the MPEG series of codecs (and MPEG4 H.264/AVC is not magically different), it’s within the realistic realm of 25-40%, which for a 20Mb/s test 1080i HD channel typically means 12-15Mb/s normal broadcast rates (hence the EBU recommendation and almost universal worldwide adoption of those bitrates for 1080i channels just as an “average” benchmark). You might need more for fast sports involving lots of pans, and you could get away with less for multi-pass pre-encoded movies / low-motion documentaries / weather reports / “stationary sports” (eg, snooker with many overhead table “stills”). But the 20Mb/s->6.7-9Mb/s the BBC are pushing for is an outrageous and totally unsubstantiated 55-67% claimed improvement which absolutely no-one is seeing in practise or swallowing the claims, either amateur viewer nor professionals running HD channels on pay-TV networks. I do not have the facilities to run one, but I’d be more than happy to participate in a double-blind 6.7Mb/s vs 9.9Mb/s vs 14Mb/s vs 20Mb/s viewing test alongside Andy, Danielle and other posters here to find out exactly what the *real* *truthful* improvement of the new codec is, because “same picture quality at 55-67% lower bitrates” it most certainly and unquestionably is not. Just for the record, I’ve taken part in double-blind (ABX) codec tuning tests re: the LAME MP3 codec in the past and I’ve used MPEG2 & MPEG4 software encoding many times (and watched different codecs evolve over time), so I do know the difference between realistic codec evolution and what’s just plain snake oil / corporate politics.

Realistically, there are 4 solutions to this absurd mess:-

1. Swallow a little pride, drop the “we’re never wrong” ego and even more absurd “the Emperor is NOT naked, you’ve all got cataracts instead” attitudes, and change the above policy to something more sane like 2-3 HD chans per mux. Either backup your claims by holding a public double-blind test of the new encoder at 9.7Mb/s vs the old encoder at 16Mb/s or stop patronizing us with “miracle” improvement claims in coding enhancements which only BBC employees seem to be see (placebo). Have the guts to tell management the truth of their “good ideas” that even 3 HD channels on a mux is pushing it once high motion live source material is used (football / motorsports / music videos). 4-5x HD channels at 6.5-8.5Mb/s each is straight out fantasy and is to speak bluntly – “DAB Reloaded”…) and plays stright into the hands of the “cut the licence fee” crowd (which is hardly in your interest as BBC-HD will end up being first in line if viewing figures remain ridiculously low). Even on Freesat, the Astra 2D sat has approx 33Mb/s DVB-S (or 43Mb/s DVB-S2) transponder bandwidth, which is still far too little (works out to 8.1Mb/s for 5 chans or 10.3Mb/s for 4 chans both allowing 500kb/s per chan for audio, subtitles, other mux / frame overhead info, etc).

2. Scrap all concept of HD on Freeview (or at least “hard split” it from Freesat HD) and lobby for the removal of the need to carry regional SD variations on Freesat, then use that freed up bandwidth for a genuine HD service on Freesat. Stop pursuing an absurd “race to the bottom” of watering down everything else on other platforms to match Freeview’s tight bandwidth in the name of “platform neutrality” (translation : “if we can’t give everyone the best of each platform, then we’ll given everyone the worst of all platforms”). Offering Freeview for regional programming and FreeSat for HD gives viewers a far more practical choice than trying and failing to force an abysmal blurred pseudo-HD on both and ending up getting laughed at and mocked all round.

3. Change to 720p. In theory it’ll use the same bandwidth, but in practise, due to less movement between (twice as many) frames (and the potential of having a higher percentage of B/P frames vs I frames per second depending on standards), it can often be broadcast at 10-20% less bandwidth vs 1080i given similar quantization errors / SNR’s. What’s more, high action sports will look a lot smoother, any deinterlacing issues will be eliminated, and there would be the option for low motion stuff (eg, news reports) to be broadcast at 25p (making everything actually look much sharper & clearer due to far lower compression artefacts / each macroblock having a higher percentage of the bitrate (and higher SNR ratio). I have seen *MANY* examples where the decrease in spatial resolution to 720 and then upscaled to 1080 only at the end by TV / box can end up looking significantly better than an attempted 1080 throughout over a grossly bandwidth starved system. It won’t cure the problem, but you’d do well to start asking yourself the question “Why does Iplayer’s HD use 720p?” to which the answer is “because they don’t have the bandwidth for 1080 – just like Freeview with 4-5 channels per mux doesn’t”.

Blurred, macroblocked 1080 is not “better” if it is less *visually sharper* and *visually clearer* than a lower resolution picture that has less “noise” (in exactly the same way a 10MP camera whose photo’s were taken at the highest res but on the LOW JPEG quality compression setting (to try and squeeze more on the memory card than is practical) can easily look much worse than a 5MP camera taken at highest JPEG quality setting and resized up to a 10MP res later on). The truth is, the difference between even good 720 & good 1080 is only really apparent on large screen TV’s when viewed up close (under 4ft) whereas rampant blocking, ringing / halo, crossfade artefacts and artificial blurring are perfectly visible at all distances on most sets down to 22″. What’s more, it’s a lot more compatible with many (even most) HD ready (1366 x 768) sets and PC’s (1280 x 800-1024) out there. Will it give the highest picture quality? No, but if that’s what the BBC intended we wouldn’t be arguing on this blog in the first place…

4. Shut down all HD programming, move 2 of the SD channels over to the HD mux, and up all BBC SD bitrates from current 3-5Mb/s to 6-7Mb/s each on all platforms. As “backward” and “outrageous” as this sounds, it will actually allow *ALL* BBC viewers with *ANY* freeview box to upscale them so that they actually look pretty good (like a superbit DVD) on modern large TFT’s without having to have any HD hardware and put an end to the silly ongoing mind games and snake oil marketing. Predicted response : “But it won’t look as good”. Correction : It won’t look as good as a 20Mb/s Blu-Ray, but then neither does the current / planned 6-9Mb/s bandwidth starved macroblocked, fuzzy, smeary, falls-to-pieces-when-anything-moves, blurred pseudo-1080…

Pick one – any one would be an improvement to most people – even drastic option 4 which would radically boost all non-HD picture quality for a majority and not just a minority. But one thing is certain – it is a total joke to seriously believe 20->14->9->6.7Mb/s is going to happen without word getting out that BBC HD (in fact all Freeview HD) is “just like DAB – *at best* not worth the money”, at worst, an appalling bad joke and an industry-wide “elephant in the room” national embarrassment. It is a huge insult to both us and the production teams of series such as Life who spend weeks filming & editing rare events in HD only for their colleagues to throw half their work in the bin at the broadcast stage. It is also mistaken to believe that these plethora of complaints are also just going to “go away” after 10 weeks by ignoring them. It didn’t work over the watery metallic underwater telephone “digital quality” of DAB, and the same is true of “fuzzy HD”.

I apologise for such a lengthy post (far longer than originally intended), but the truth is, whilst no-one expects BBC-HD to match 20-30Mb/s Blu-Ray, and whilst many would grudgingly accept a realistic compromise of 3x 11.5Mb/s channels per mux, no-one is seriously going to accept a drift into la-la-land of “glorified Youtube quality” 6.5Mb/s for a service whose sole justification for its existence is based on superior picture quality over SD.

This entry was posted on Tuesday, December 15th, 2009 at 11:56 am and is filed under BBC HD. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.