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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. "
Try watching a football game here in the US and you will see what crap quality can be. The turf turns into squares of blur when the camera moves, then returns to blades of grass when the picture is stationary. As soon as you spot it you will hate it. If you don't see it then OK for you.
I used to have a friend who could spot the two little circles in the top right of a movie in the theater telling the projectionist to change the reel. Once he saw them the movies were never the same again.
If you're watching a soap opera, you only need to see a few frames per week to follow the story. If you are watching a live sports event with a lot of action, most people will notice every dropped frame and compression artifact (I've noticed myself while watching the Olympics via satellite feed.) Methinks they did the testing on a relatively static video. Video compression works by (among other methods) creating a key frame, then sending diffs off that key frame for several frames. If every frame is completely different, compression does not work well.
I've abandoned my search for truth; now I'm just looking for some useful delusions.
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
Lossy compression formats depend on an understanding of human perception. Nobody has a perfect model of the human brain, and nobody has a perfect algorithm for deciding what data to keep and what data to throw away.
If you have a better model of human perception than your competitors, then your encoder will yield higher quality output. If you spend 50% of your bits on things that nobody will notice, and I spend 25% of my bits on things that nobody will notice, then my 650kbps stream is going to look better than your 900kbps stream.
LAME did not win out as the MP3 encoder of choice just because it is free. It won out because its psychoacoustic model yields better-sounding MP3s at 128kbps than its competitors managed at 160kbps or even 192kbps.
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
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".
BBC HD also uses H.264 for terrestrial and satellite broadcasts. It's only if you have Virgin Media cable that you get the stream transcoded to MPEG-2.
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Aren't you comparing x264 to oranges?
Adding to that, Comcast's programming is 720p, with much of it upscaled. The Blu-Ray source you see at the stores are often 1080p, or at least 1080i. You're comparing rotten wormy apples to nice juicy oranges, where Comcast's feeds are the rotten wormy apples.
The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
A codec is a compressor/decompressor piece of code that's used in one of two circumstances-- lossy or non-lossy stream compression, usually (but not always) of audio/video information. The eye and ear can detect certain types lossy compression effects, and some people are better at detecting problems than others. Generally, more compression yields more information loss that is sensed by low quality video (jaggies, weird frame transitions, noise, fewer colors, or distorted sound of various kinds). But more compression means less bandwidth used, so that more streams can be handled per given bandwidth 'space'.
In the US, the current max horizontal by vertical HD TV resolution is 1080 pixels, and its data rate at full color value is about 16megabits/sec. There are two types, interlaced and progressive scans. Interlaced writes and holds information from frame to frame while progressive writes whole frames (a simple explanation) and progressive is preferred but requires more intelligent electronics to produce. The 1080p HD picture is preferred. An interim size, 720p, is often what cable companies send down the wires to your set. The native resolution refers to the uncompressed data rate, or one that's used with a non-lossy compressor (meaning that the decompressor can re-interpret the compressed stream to reproduce the original image 100%).
---- Teach Peace. It's Cheaper Than War.
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.
Theoretically, perhaps. In reality either one could look better given other factors.
"Growing old is inevitable; growing up is optional."
My cranium nearly exploded while attempting to parse
My office has been taken over by iPod people.
Actually, the bandwidth at 8bits per channel not including the 5.1 sound is 16,588,800 bits per FRAME not per second, so at 60 FPS you get a 950 mb/s bandwidth requirement for the video alone, and that`s why we need to use a compressed distribution method...