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BBC HD Response Regarding Picture Quality (BBC HD Blog)


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Old 17-09-2009, 17:30
Snoods
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Now on Danielle's BBC HD Blog.

http://www.bbc.co.uk/blogs/bbcintern..._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.
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Old 17-09-2009, 18:11
alan.w
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Thanks Dad
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Old 17-09-2009, 18:26
mossy2103
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One good point that needs a wider audience (the bolding is mine, not the author's):

While very clear, sharp images have become closely associated with HD, it is important not to confuse "sharpness" with resolution. The use of electronic sharpening on standard definition pictures can make images clearer but does not increase the amount of information in the picture, one of the defining features of HD.

Electronic sharpening is not a characteristic which BBC HD encourages since we prefer images to look more natural, and to allow directors to offer contrasting focus in order to highlight the key features in a scene. Indeed, some of our dramas are now using the latest large image format cameras.These cameras use an image sensor about the same physical size as a 35mm film frame that gives the image a very shallow depth of field. This will put all but the key subject out of focus and allows a director to use focus as a story telling tool.

HD picture quality is not purely about a crispness of image, but about a richness of image which comes from the amount of detailed information included.
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Old 17-09-2009, 19:44
scoobiesnacks
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One good point that needs a wider audience (the bolding is mine, not the author's):
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.
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Old 17-09-2009, 20:11
jzee
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One good point that needs a wider audience (the bolding is mine, not the author's):
Thanks Mossy, all that is essentially waffle and excuses. The fact is THIS

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?
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Old 17-09-2009, 20:22
scoobiesnacks
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Thanks Mossy, all that is essentially waffle and excuses. The fact is THIS

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/bbcintern..._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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Old 17-09-2009, 20:56
jzee
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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/bbcintern..._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
I refuse to post on there because I don't believe it will do any good. A mistake has been made, and neither Danielle or Andy are going to admit it because it would damage their professional standing. The error will be even more serious if they have already leased out the remaining space to another broadcaster. This will leave us in the position where the Freeview HD BBC HD will be superior from the beginning of its transmission in December. One could then ask questions about whether they are deliberately hobbling the quality of the satellite BBC HD in order to give a boost to sales of Freeview HD boxes. That would be a completely unacceptable corruption of public funds if that is the case. Most people on the Sky HD forum disagreed with Danielle about the Athletics by the way (I can't say one way or the other as I don't have Eurosport).

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post 2

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Old 17-09-2009, 20:59
scoobiesnacks
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I refuse to post on there because I don't believe it will do any good. A mistake has been made, and neither Danielle or Andy are going to admit it because it would damage their professional standing. The error will be even more serious if they have already leased out the remaining space to another broadcaster. This will leave us in the position where the Freeview HD BBC HD will be superior from the beginning of its transmission in December. One could then ask questions about whether they are deliberately hobbling the quality of the satellite BBC HD in order to give a boost to sales of Freeview HD boxes. That would be a completely unacceptable corruption of public funds if that is the case. Most people on the Sky HD forum disagreed with Danielle about the Athletics by the way (I can't say one way or the other as I don't have Eurosport).

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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.
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Old 17-09-2009, 21:33
jzee
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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.
Feel free to use any of that information I posted. The information on the encoder was from here originally linked to here. Admittedly the story was from 2006, so we can't be sure but I think it's likely they just received an upgrade to the Vibe encoder not a completely different model. The fact is, as I stated that BBC HD on satellite now has the lowest bitrate in the whole of the UK for a live encoded HD channel- the closest is ITV HD but we don't pay ITV 142 a year! All of the rest go up to at least 13Mbps when needed.

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?"
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Old 17-09-2009, 22:08
Orbitalzone
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Just a thought, is this so they lower HD resolution that'll be on Freeview will compare better to the satellite equivilent?
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Old 17-09-2009, 22:14
jzee
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Just a thought, is this so they lower HD resolution that'll be on Freeview will compare better to the satellite equivilent?
If the Freeview version will be using 720p, it will have an even better picture quality as the bitrate will be able to go up to 12-13Mbps when needed while the 1080i BBC HD on satellite will be stuck at 9.6

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? Hmm perhaps I should go and post on there myself.
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Old 18-09-2009, 08:52
mossy2103
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Thanks Mossy, all that is essentially waffle and excuses.
As you wish. Just pointing out other relevant facts that can affect PQ (I prefer to have discussions based upon facts rather than anything else). If the facts then don't fit the opinion, that's not a problem for me.
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Old 18-09-2009, 11:15
jzee
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As you wish. Just pointing out other relevant facts that can affect PQ (I prefer to have discussions based upon facts rather than anything else). If the facts then don't fit the opinion, that's not a problem for me.
Mossy the point I am making as I hinted on another thread is that they are completely trying to divert people from the main issue which is compression artifacts otherwise known as blocking or pixellation that occur when something is encoded either too fast and/or without access to enough bitrate. The BBC have set the rate too low so in demanding scenes we get these compression artifacts showing up which completely spoils the point of HD.
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Old 18-09-2009, 11:33
BKM
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I refuse to post on there because I don't believe it will do any good. A mistake has been made, and neither Danielle or Andy are going to admit it because it would damage their professional standing. The error will be even more serious if they have already leased out the remaining space to another broadcaster.
I would agree with this totally! Reading Danielle's blog it sounds to me that they have been told to do the best they could in the bit rate they are currently using - and that they thought they had it cracked!

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.
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Old 18-09-2009, 13:05
Widget76
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If the Freeview version will be using 720p, it will have an even better picture quality as the bitrate will be able to go up to 12-13Mbps when needed while the 1080i BBC HD on satellite will be stuck at 9.6

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? Hmm perhaps I should go and post on there myself.
Maybe someone registered on there should ask him to name those sites. Im certainly not aware of anywhere currently complimenting the BBC HD output.
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Old 18-09-2009, 14:26
Jaycee Dove
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I am puzzled as to why there is an argument that the BBC would want Freeview to be of equal or better quality for BBC HD than on satellite?

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.
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Old 18-09-2009, 18:51
scoobiesnacks
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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.
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Old 19-09-2009, 18:52
White-Knight
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I am puzzled as to why there is an argument that the BBC would want Freeview to be of equal or better quality for BBC HD than on satellite?
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.
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Old 19-09-2009, 19:34
derek500
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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.
The original film stock has a greater resolution than HD, but it's still an expensive job converting it for HD broadcast.
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Old 19-09-2009, 20:11
snappysnaps
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Strickly come dancing is stunning tonight in BBC HD
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Old 19-09-2009, 20:20
jzee
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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.
The bandwidth of a DVB-T2 transponder will be 36.1Mbps (source: BBC blog). Therefore at the start with BBC HD, ITV1 HD and C4, the average bitrate will be 12 going up to 15-16Mbps. When Five joins the average will be 9 going up to 12-13Mbps. So the Freeview HD channels will be able to increase their bitrate at least 3-4Mbps above the level that the satellite BBC HD is currently stuck at and will not suffer from the same level of compression blocking on difficult scenes i.e. shadows or large or numerous fast moving or changing subjects, and interlaced more than progressive filmed sources that we are currently seeing on the satellite BBC HD.

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.

Strickly come dancing is stunning tonight in BBC HD
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.
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Old 19-09-2009, 22:38
GlynM
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The bandwidth of a DVB-T2 transponder will be 36.1Mbps (source: BBC blog). Therefore at the start with BBC HD, ITV1 HD and C4, the average bitrate will be 12 going up to 15-16Mbps...
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

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.

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Old 20-09-2009, 00:49
White-Knight
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Sorry for the noob question but when we're talking transponders aren't we still talking satellite and not terrestrial Freeview? Its Freeview where the problem lies and that's because of the governments sell off of the analogue spectrum leaving only the existing digital portion to suddenly host 4 HD channels.

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.
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Old 20-09-2009, 02:08
jzee
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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
The AC3 sound track on BBC HD recently dropped to 192kbps (used to be 384 I think), the MPEG2 track is 256- that means about 0.5Mbps for each channel's audio. Your figure for DVB subtitles seems far too much- 200k for a digital stream of words? As for the red button I have no info on that so cannot agree or disagree. If the average is indeed around 9.6 for 3 channels - the fact is it will still be able to rise to around 13-14Mbps for demanding scenes where the satellite version won't. If they want to make the two channels equal they either need to raise the fixed rate on satellite or switch to S2 and stat mux.

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!
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Old 20-09-2009, 08:43
GlynM
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...Your figure for DVB subtitles seems far too much- 200k for a digital stream of words?

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.

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