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BBC Lowers HDTV Bitrate; Users Notice
aws910 writes "According to an article on the BBC website, BBC HD lowered the bitrate of their broadcasts by almost 50% and are surprised that users noticed. From the article: 'The replacement encoders work at a bitrate of 9.7Mbps (megabits per second), while their predecessors worked at 16Mbps, the standard for other broadcasters.' The BBC claims 'We did extensive testing on the new encoders which showed that they could produce pictures at the same or even better quality than the old encoders ...' I got a good laugh off of this, but is it really possible to get better quality from a lower bitrate?"
They also lowered their math standards. From 16MBps to 9.7 MBps is a 40% reduction, not "almost 50%".
I've abandoned my search for truth; now I'm just looking for some useful delusions.
Sure, if you also switch to a better codec, such as using H.264 instead of MPEG-2. However, I don't think that's what's happening in this case.
Any lossy compression works by throwing away bits of the picture that the viewer might not notice. You can lower the bitrate with better psychovisual and psychoacoustic models. You're still throwing away more information, but you're doing it in a way that the user is less likely to notice. This takes more CPU time on the compressor, a more optimised encoder, or a better algorithm.
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It's not impossible to get better results out of lower bitrates, but you have to pay the penalty elsewhere, typically in encode/decode complexity.
If your decode hardware is fixed (it's generic HDTV hardware), then there is much less room for improvement, and half the bitrate is an enormous drop. It's no surprise that the BBC viewers complained.
I read the internet for the articles.
Nitpick: So 39% is "almost 50%"?? I would have called that "almost 40%". Then again that is a /. summary.
After logging in slashdot still does not take you back to the page you were on. It's been that way for 20 years.
They just remove the naughty bits.
Bitrate is only part of the equation -- the H.264 spec allows for a number of different ways to compress video, and it's up to the encoder to find out which is best for your video. Even in the same encoder, you can tweak dozens of settings in ways that dramatically change output quality -- usually a trade off between time and size.
x264 has beat every commercial encoder out there -- in some cases, on a level that would indeed render higher quality with half the bitrate.
FTA: ""Even my wife can see a reduction in picture quality and she's got cataracts," wrote one. "
You can also get better compression by specifying a more sophisticated compression method within the same codec, for example, since many codecs support various levels of compression.
Generally, "better" compression (fitting a higher resolution and/or framerate into a smaller size) requires a lot more power to encode and often some more power to decode. You can use less bitrate to get a quality signal there, but you need "smarter" coders and decoders at the respective ends of the transmission. So the BBC may have upgraded their compression engine to something that can do "better" compression, thereby fitting the same resolution and framerate into a 40% smaller stream. But their customers' television sets might not have the horsepower to decode it at full quality.
That could easily explain why the BBC's testing went so well but their consumers (with varying brands of TV sets probably mostly tested for British use with the old compression) can't keep up and render an inferior picture.
It's also possible that, by compressing the video stream into a denser compression method, signal loss is having a greater effect than it did with the old compression method. The viewers may be seeing artifacts that are the decoder's attempts to fill in the blanks. The old compression method might have allowed a certain amount of redundancy or error correction that the new one lacks, and the loss of part of the signal has a more visible effect on the new one.
"This post contains words, known to the State of California to cause thought. Wash brain thoroughly after reading."
was the featureless black-screen video to 4'33" from John Cage. Results were far better at the lower bitrate. The absolute darkness was less blurry.
Nullius in verba
Yes, it IS possible to get higher picture quality out of a lower bitrate, but not with all else equal. For example, you can get higher quality with CPU-intensive settings using H.264 5.1 Profile than you can with H.264 4.1 (what Blu-Ray's/HD DVDs use), at the same bitrate. You're giving up CPU cycles in decoding for lower video size. This is why x264 can produce near-transparent encodes of Blu-Ray movies at about half the size. x264 uses much more demanding settings.
x264 at 20 Mbit which high-quality settings is far more demanding than a 40 Mbit H.264 stream from a Blu-Ray.
FTA: ""Even my wife can see a reduction in picture quality and she's got cataracts," wrote one. "
They must have a pretty big screen if she can see that difference from the kitchen.
In other words, lower bitrate can be better, but only if you compare to shitty and inefficient compression.
And by this you mean compression that is state of the art two minutes ago, vs. today. Seriously, this field is moving pretty fast, and what you call shitty and inefficient was not long ago the best people could do. A few years ago when I was messing with the x264-svn libraries, stuff would get tweaked daily.
Not to mention there are other factors at play with regards to compression. A well-engineered system isn't necessarily going to go for the maximum compression rate for video quality. One has to look at other limitations, such as the decoding hardware, the method by which the video is being delievered, and even the viewing devices on the receiving end.
What is disheartening about the article is that it looks like the BBC are just in denial mode, and not really taking the complaints seriously. "Standard viewing equipment"? Seriously, what exactly are they getting at with that comment? On top of that it looks like they are trying to blame the quality of the source material, which certainly muddies the picture, but certainly the customers that are complaining would be used to these variations in quality before the change and not just suddenly notice it at the same time this equipment was rolled out.
I have respect for them sticking to their guns, but not when they are doing it with such lame excuses. Then again, the BBC spokesperson and reporter may not be the most tech savvy individuals, and its likely some of the message here is lost in translation. Lossy codec indeed.
Public: Shou£dn't you be ta£king in our £anguage?
Windows 3.1x calc: 3.11 - 3.10 = 0.00
I think you might want to talk to you cable company on that one. I know the effect you are seeing (it's by far the worst on local Public TV since they crammed 7 sub-channels into the same carrier), but network TV coverage of football in my area is pretty pristine for the most part. OTA is even better but cable is still awfully good.
Of course, by "talk to your cable company", I mean "do nothing" because talking to the cable company is a complete waste of time.
Brett
In the US, Comcast uses codex compression to squeeze HD on their cable systems. When people get to see native resolution at the TV store, then get the Comcast version when they plug in their shiny new HD TV, they wonder WTF? That the beeb would put their foot on the garden hose and expect no one to notice is ludicrous.
I wish the FCC would get involved in the US to force cable companies to limit the number of channels supported and broadcast them in the highest sustainable resolution-- or tell their users the truth about what's happening and why. Maybe we can start to get rid of the excess junk channels.
---- Teach Peace. It's Cheaper Than War.
Actually, deary, it's sexist, not racist. I swear it's not making me take you less seriously though.
Support the EFF and Creative Commons. The war is coming, and they're supporting you...
1) The alleged wife in the quote is purported to have cataracts. Cataracts typically reduce visual acuity due to the cloudiness they impart to the lens of the eye. How does a reduction of visual acuity translate to "just another racist characterization of women being incompetent with technology"?
2) If the quote had been ""Even my husband can see a reduction in picture quality and he's got cataracts," wrote one." would you have bothered to make your little rant post?
P.S. The term you were looking for is "sexist" not "racist".
Aren't you comparing x264 to oranges?
As a 3 yo lesbian, father of seven, socialist COBOL programmer, I'm not sure which of your stated attributes qualify you to be racially offended.
My cranium nearly exploded while attempting to parse
My office has been taken over by iPod people.