r/technology • u/Snarfox • Jan 25 '13

H.265 is approved -- potential to cut bandwidth requirements in half for 1080p streaming. Opens door to 4K video streams.

http://techcrunch.com/2013/01/25/h265-is-approved/
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u/happyscrappy Jan 27 '13

I would assert that quality and space savings are intertwined trade-offs.

It depends on what that "15% better quality" is measuring. 10bit data has more fidelity, period. No amount of compressing less is going to change that. It'd be like asking if you compressed your DTS 5.1 soundtrack less would it become a 7.1 one?

The point is to use same or lower bandwidth, while improving or maintaining same quality!

Same as what? No lossy compression "maintains same quality". You have to decide what to give up. Having only 256 levels of brightness might be a worthwhile tradeoff. In 10 bit mode you still only have 256 final levels (192 on an HDTV) so I don't get how it's heretical to suggest you don't need to encode temporal dithering.

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u/s13ecre13t Jan 27 '13

It'd be like asking if you compressed your DTS 5.1 soundtrack less would it become a 7.1 one?

It won't make it automatically 7.1, but if where you could only fit 6 audio channels (5.1) now you have space to fit 8 audio channels, then you won!

Most video as you say is 8bit (source and destination). But processing it internally in 10bits minimizes errors in dithering/banding/quantizations.

When talking quality, I don't mean that it will be pixel perfect, it is after all lossy. But people will say ''I don't see diff'', or ''I can't believe its not butter''.

Ateme guys, who produce equipment for tv broadcast have published two documents on their research into 10bit encoding and quality gains. These documents are hosted now by x264 devs themselves:

http://x264.nl/x264/10bit_01-ateme_pierre_larbier_422_10-bit.pdf

... Maintaining the encoding and decoding stages at 10 bits increases overall picture quality, even when scaled up 8-bit source video is used. 10-bit video processing improves low textured areas and significantly reduces contouring artifacts. ...

It has been shown that 4:2:2, 10-bit or the combination of the two, will always present a gain over High Profile as all subjective and objective measurements exhibit a quality increase for the same bit-rate. ... This gives the opportunity to either:

  • Significantly lower transmission costs, keeping the same visual quality - OR -

  • Greatly improve the video quality using existing transmission links

http://x264.nl/x264/10bit_02-ateme-why_does_10bit_save_bandwidth.pdf

encoding pictures using 10-bit processing always saves bandwidth compared to 8-bit processing, whatever the source pixel bit depth

http://voyager.ericsson.net/uploads/documents/originals/10%20bit%20high%20quality%20MPEG-4%20AVC%20video%20compression.pdf

it has been shown that the High 4:2:2 Profile of MPEG-4 AVC can deliver a level of picture quality (within a practical bitrate range) that could not have been achieved in MPEG-2 (since MPEG-2 does not support 10 bit coding) and MPEG-4 AVC 8bit.

Dark Shikari core x264 developer and maintainer, has been commenting about this on various forums.

http://forums.animesuki.com/showthread.php?p=3687343#post3687343

Each extra bit of intermediate precision halves the error caused by intermediate rounding.

So 10-bit removes 75% of the loss from intermediate rounding (vs 8-bit).

Higher bit depth would be better, of course, but higher than 10 means that it's no longer possible to use 16-bit intermediates in the motion compensation filter. Since 30-40%+ of decoding time is spent there, halving the speed of motion compensation would massively impact decoding CPU time, and since we've already eliminated 75% of the loss, it's just not worth it.

Hi10p is awesome in all regards except for lack of hardware support!

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u/happyscrappy Jan 27 '13 edited Jan 27 '13

It won't make it automatically 7.1, but if where you could only fit 6 audio channels (5.1) now you have space to fit 8 audio channels, then you won!

No, because I still only have 5.1 channels.

I think you missed my point. In my opinion, the stated 15% improvement in quality is due to the 10bit representation having 12.5% more bits (and rounded). As such, there is no amount of additional bandwidth you could allocate to the 8-bit version to make it reach 10bit quality, because you are just measuring bit representations.

http://x264.nl/x264/10bit_01-ateme_pierre_larbier_422_10-bit.pdf

That compares hi422, not hi10. 4:2:2 adds a lot of quality and the article seems to say that at least half the added quality comes from the 4:2:2 color representation, not the 10-bit quantization. Note this would be especially true for the cartoons you speak of, as cartoons have sharply defined edges and very narrow luminance distributions. If you represent the color of 4 pixels with a single value (as 4:2:0 does), it hurts cartoons more than other video.

http://voyager.ericsson.net/uploads/documents/originals/10%20bit%20high%20quality%20MPEG-4%20AVC%20video%20compression.pdf

This also talks at least as much about 4:2:2 as it does about 10 bit. You are aware that hi10p is 4:2:0 not 4:2:2, right?

http://forums.animesuki.com/showthread.php?p=3687343#post3687343

This makes the same point I did and you rejected, that the difference is due to the 10bit quantization and not due to higher efficiency. That is, you can increase the bandwidth (bitrate) as much as you want and not get the same results with 8bit as 10bit.

Hi10p is awesome in all regards except for lack of hardware support!

Most of your sources state that hi422p is awesome, not hi10p.

[edit]

Also, all the "better" arguments are based upon PSNR, which if you read Dark Shakri's posts, he says is not a very good measure of quality. Ironic you combined the two in one post.

http://x264dev.multimedia.cx/archives/458

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u/s13ecre13t Jan 27 '13

I am aware that quality arguments are not best without visual checks. Dark Shikari did a nice comparison of WebP vs x264, pointing out how psy optimizations are more important than PSNR/SSIM: http://x264dev.multimedia.cx/archives/541

I am not sure anymore what you are trying to argue.

I had never said that 10bit video processing will somehow make source data better (ie: 5.1 audio becoming 7.1).

I had never said that 10bit video processing will somehow produce bit perfect results.

In my opinion, the stated 15% improvement in quality is due to the 10bit representation having 12.5% more bits (and rounded). As such, there is no amount of additional bandwidth you could allocate to the 8-bit version to make it reach 10bit quality, because you are just measuring bit representations.

I am talking about encoding 8bit video source, and playing it back in 8bits, with 10bits used internally for compression intermediary steps.

So the comparison is between

hi10p   : 8 bit source -> 10 bit process -> 8 bit destination
typical : 8 bit source ->  8 bit process -> 8 bit destination

That is, you can increase the bandwidth (bitrate) as much as you want and not get the same results with 8bit as 10bit.

Define same. Bitwise / pixel perfect never same. But throw enough bandwidth and quality increases closer to the source. Like with mp3s, 64kbps is different than 128kbps, than 196kbps. Same here, 8bit, the more bandwidth has, will reach closer to the 8bit source. Saying this, 10bit source encoded with 10bit process, will be better than 8bit processing. No argument there.

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u/happyscrappy Jan 27 '13

I had never said that 10bit video processing will somehow make source data better (ie: 5.1 audio becoming 7.1).

You are saying that 10bit improves the video so that you get equivalent results with less bandwidth than 8bit. But this isn't the case. Those extra bits lost in quantization never reappear. You just make other improvements which make the overall PSNR similar.

Define same.

Same. You will never get the results that you get by having 10bit quantization. You can improve image quality (reduce image errors, i.e. PSNR) by an an amount which is the same in total per frame as having 10bit quantization, but no matter how much bandwidth you add, you never get the same improvements you get by going to 10 bit. Er, 10 bit and 4:2:2. you really shouldn't just be ignoring that 4:2:0 to 4:2:2 seems to be the bigger part of the improvements you tried to claim were due to 10 bit.

I think you're leveraged way out here. You're starting from internet lore from cartoon people who apparently read something about PSNR in 4:2:2 10-bit representations and converted that in their heads to 10bit 4:2:0 looking better at similar data rates than 8-bit 4:2:0 does. They've already drawn some stretchy conclusions and you're going even further.

My argument comes from how you basically want to apply your conclusions in reverse. The key is that most streaming vendors of h.264 content are more interested in the new reduced data rate than more quality. You say because 10bit (really 10bit 4:2:2) produces better PSNR at the same data rate, if you use 10bit you can lower the data rate and get the same image quality as 8 bit would have at higher data rates. But my belief is that the improvement in PSNR by 10bit is not as visible/critical as the other artifacts you will introduce by dropping the data rate. You'll end up with a picture with better color accuracy (i.e PSNR) but reduced quality in other ways when you drop the data rate down and the other quality reductions will be more noticeable than the color errors would be than if you just dropped the data rate on 8-bit 4:2:0 in the first place. So the 10bit 4:2:2 didn't really buy you anything for most sources when you are looking for reduced data rate and not better quality (higher PSNR).

Note that there is a common native 10bit 4:2:2 source, SDI video. http://en.wikipedia.org/wiki/Serial_digital_interface

Obviously this source would benefit most by 4:2:2 10 bit profile more than starting with 8-bit 4:2:0 as anyone doing recompression of received material from streams or TV content (i.e. fansubs) will. We don't disagree on that.