BBC HD Response Regarding Picture Quality (BBC HD Blog)
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Now on Danielle's BBC HD Blog.
http://www.bbc.co.uk/blogs/bbcinternet/2009/09/picture_quality_on_hd_a_respon.html
Just sharing , as i know a lot of viewers were waiting for a response from them.
Still not really saying anything has changed quality wise though are they ? We clearly know it has. :rolleyes:
http://www.bbc.co.uk/blogs/bbcinternet/2009/09/picture_quality_on_hd_a_respon.html
Just sharing , as i know a lot of viewers were waiting for a response from them.
Still not really saying anything has changed quality wise though are they ? We clearly know it has. :rolleyes:
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People think the pictures is frequently soft, lacking in detail, noisy and with compression artefacts.
The bottom line is it is primarily a bitrate problem as far as I'm concerned. They are running the channel at a bitrate that is lower than comparible channels. It must have an impact.
BBC HD now has the lowest bitrate out of all 'live' HD channels in the UK (i.e. excluding Luxe)- I believe somebody has clearly made the mistake of setting the level at what will be the average of rates on Freeview HD - this completely misses the point of stat muxing that when the channel needs more bitrate, it can increase and when it doesn't need it (i.e. at an a extreme a black screen with a white block in the middle) it drops so the Freeview HD BBC HD will have access to 3-4 more Mbps when needed in more difficult material and the picture will be significantly better.
The channel that is used a case study for the encoder the BBC are using (the Thomson GrassValley) is Eurosport HD. I quote from the Thomson GrassValley case study:
"The Thomson ViBE MPEG-4 HD encoder is equipped with a unique embedded Mustang chipset that allows Eurosport to broadcast HD video in an unrivalled quality in a bandwidth as low as 4 Mb/s."
That may make you think wow 4Mbps - that's amazing! But it isn't actually amazing at all- if you look at the bitrates of Eurosport HD at 19.2, 23.5 and 28.2 satellite positions 4Mbps is the lowest the rate ever drops to- 28.2 rises to 20Mbps, 19.2 and 23.5 to 15Mbps.
So, the case study on the channel for the encoder the BBC is using can climb at least 5Mbps higher than the current level of BBC HD- how can the BBC continue to argue that they have set the correct bitrate level for this encoder?
That's very interesting. Because in Danielle's blog she argues that the same World Athletics Championships broadcast was better PQ on BBC HD to Eurosport. So if they are using the same encoder how could that be?
http://www.bbc.co.uk/blogs/bbcinternet/2009/09/picture_quality_on_hd_a_respon.html
Would you be prepared to post this to Dannielle's latest blog and ask them to respond? I notice Andy Quested is answering questions on there tonight, so you could direct this as a question to him maybe
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I agree its a waste of time posting to their blog
But the information you have here could be useful to the BBC Trust complaint that is being prepared.
It was in part the threat of a BBC Trust complaint that triggered Dannielle's response.
Are you sure the encoders are the same for Eurosport and BBC HD? The exact same model? Because if they are , then as you say it sort of tears a hole through her defense of picture quality.
Perhaps you could ask Andy/Danielle this simple question:
"Why have BBC reduced the bitrate when they already pay for a whole transponder of bandwidth? The BBC are essentially now paying for 7Mbps of unused bandwidth-- why?"
EDIT: I notice Andy Quested has now posted
"There are sites that say the quality is good and there are sites that would prefer we used no compression at all"
Which sites? Where has anyone stated no compression should be used:rolleyes:? Hmm perhaps I should go and post on there myself:D.
While what she says about improving encoder technology is all correct it certainly looks to me that their bit-rate cut has been too drastic and has exceeded the capabilities of the improved encoders.
Maybe someone registered on there should ask him to name those sites. Im certainly not aware of anywhere currently complimenting the BBC HD output.
Is not BBC HD stated to be platform neutral?
I can only imagine that if they have reduced bandwidth then that is a purely financial decision.
And they should be asked to clarify if that is the case, because I doubt they will want to undermine their case for increased licence funds.
Although it could be argued that cutting costs for BBC HD alongside cost cutting with other BBC channels is good business in a recession.
This argument always intrgues me as its used outside this debate. The BBC is on a fixed income compared to most businesses. Not that they shouldn't cut costs, I do agree with that, but the recession surely doesn't impact their income. In fact, the population is increasing in the UK, as is the number of households, so I'd expect their income is increasing.
I accept I'm going on topic here though.
Well non of this is proven but I think its arisen because Freeview has known bandwidth problems that mean that it simply (allegedly) can't support the same bit rates as are currently on Freesat. So the BBC have a choice leave Freesat as better quality or reduce quality to match that of Freeview. Some of us have long since argued the 2nd option is fundamentally wrong, to deliberately reduce a picture to match the lowest common denominator. I personally believe that in a situation where Freeview's plight is only going go get worse, the way to go is to let Freesat stand as a stand alone platform and provide the quality option with max HD channel choice and let Freeview stand on its ease of installation.
In case your wondering what I mean by going to get worse - picture this, Freeview only has room for 4 HD channels and even thats a squeeze. So you're going to see BBC HD, ITV HD, CH4HD and 5HD when they arrive. However, more and more channels are going over to HD because thats what the demand is for and figures show where the growth is. So what happens when eg. FIVE US goes HD on the back of FIVE HD's success? - Most of its content is already HD so such a change is likely. Same with FILM 4, all films are already above HD resolution so its highly likely if 4HD is popular that FILM 4 will follow suit. What is Freeview going to do with insufficient space to host these? Let them be lost to Sky? Remember, there's always the risk with some of these second channels that they might go exclusively HD to save costs as simulcasting SD cost more money.
My argument to save them as FTA is host them on Freesat which has room for 6 or more HD channels and even more if a deal to move the Sky encrypted content off 2D can be struck. That way at least they stay FTA and people then have a choice of platforms, Freeview for ease of installation or Freesat for Max HD and Max quality. Kind of a normal vs enthusiasts platform choice. Those who are in no reception areas for Freeview still get the benefits of Freesat, in fact more benefits than currently so Freesat satisfies the BBC brief on that one and people with Freeview get a choice of staying with Freeview with 4xHD channels or going for the option of Freesat with more, rather than the current potential to lose access to several of the most popular channels, altogether so with this plan everyone comes out a winner.
The original film stock has a greater resolution than HD, but it's still an expensive job converting it for HD broadcast.
It is still my opinion that the error they made was to think it would be sufficient to set the level at the average of the Freeview HD stat muxed rate, this was completely wrong as it doesn't matter what the average is, it matters what the maximum rate is if you are going to compare to a fixed rate channel.
That is not much of a problem for the encoders with spotlights on the dancers. Movement and complex patterning in shadow is harder to compress.
I think that might be a little over simplified. You have to remember that there are other components fighting for space on the mux.
At a mux level there is the actual and cross-carried SI data and PSI, around 600kbit/s. The final multiplexer needs some headroom to work in, lets say 1%, 360kbit/s.
At a service level AC3 audio 425kbit/s, audio description, 67kbit/s, HD DVB subtitles - 200kbit/s. You also need some space for the red button applications and given that these services are from different providers then it can't be shared across the services. Looking at a current BBC Mux suggests around 1.5Mbit/s which here will be needed on each service.
So at a mux level:
Mux overhead - 360kbit/s
SI/PSI - 600kbit/s
leaving 35.14mbit/s for services
And at a service level:
AC3 sound - 425kbits/s
Audio Description - 67kbits/s
HD DVB subtitles - 200kbits/s
Red button - 1500kbits/s
Giving a total of 2.19Mbits/s
For 3 services this leaves a video pool size of 28.57Mbits/s giving an average per service of 9.52Mbits/s which sounds close to the constant bit rate of 9 that is creating the complaints :rolleyes:
I don't have experience of any HD stat-muxes but assuming it is similar to an SD stat-mux then you have to define a pool size, then for each service a minimum & maximum bitrate and some sort of priority or quality setting.
The best a stat-mux can allocate is one service at max and the others at min. I have no feel for what the minimum for HD should be. If it was, say, 6Mbits/s then for 3 services this would allow a max of 16.57Mbits/s.
I guess there is some scope for squeezing the mux overhead with modern multiplexers and possibly reducing the red-button allocation but really what I'm trying to point out is that there are lots of small components as well as the HD video that add up to something significant.
Glyn
My understanding is that they never intended Freeview to host any HD as HD wasn't even in mind when they allocated spectrum and standards for Terrestrial Freeview. However they have managed it but only because of the advent of DVB-T2 compression. However, once that new space created by the greater compression is filled, Freeview has no where else to turn to for bandwidth which means no more HD and probably no more (or not many) SD channels either.
Its only when you consider that, that you realise where I'm coming from when I say Freesat needs to be a standalone platform unconstrained by the problems with Freeview.
You could ask why does the satellite version need to be reduced to match the Freeview, when iplayer certainly is not also equal? If the satellite BBC HD did end up having a better picture it's not as if people would be forced to use a propriety subscription platform to get it - that is the whole point of Freesat!
But DVB subtitles are a digital stream of the the bitmap of the displayed words (I think an original objective was to be able to include graphic objects) and HD DVB subtitles require twice the bandwidth of SD DVB subtitles.
I think this HD stat-mux is going to struggle. Stat-muxes need help to be efficient. This includes a diverse set of services to provide a mix of easy and difficult to code material. Alternatively prioritisation is applied, where premium services are given more bitrate. This can be done at the stat-mux or by adjusting the video resolution.
However none of this applies in this case. All the services are probably going to be of similar content and I'm sure that the mux operator is going to be obliged to demonstrate fair and equal allocation of resources across the different service providers. I suspect, and I would love to be proved wrong, that this stat-mux will be struggling to peak beyond half way between the average and theoretical maximum, say around 12.5Mbit/s in my example.
Glyn
The picture for Strictly certainly was stunning last night again, however the sound was a big problem. For the first two thirds of the show we had intermittent breaks in the sound, a couple of times per minute, gradually becoming less frequent as the show went on, but continuing the entire duration of the show.