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Old 12th March 2021, 23:10   #1  |  Link
burban
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hevc-aq "production-ready"?

Hi,
my current goal is to encode my bluray collection with x265 for easier inhouse streaming. Upon research for good baseline settings I stumbled across the "hevc-aq" option of x265. I could find a few sources stating that it is experimental and not suitable for "important" encodes yet. But it's been a while and it doesn't seem to be experimental anymore, but I also couldn't find any real world tests with it.
So I decided to take a look myself.
I extracted a 5 minute segment from an action movie bluray that contains fast paced action, slow camera movements, dark and bright scenes, landscape shots and close ups. I encoded it with different settings and the results where impressive:
  • Source: 27.5 Mbit/s (1006 MB)
  • x265: 6520 Kbit/s (238 MB)
  • x265 deblock=-1,-1: 6515 Kbit/s (238 MB)
  • x265 hevc-aq: 2565 Kbit/s (92 MB)

Common settings for all encodes:
  • Version: x265 3.4+2-g02d2f496c
  • Preset: slower
  • Profile: main10
  • Level: 5.0
  • CRF: 20
  • no-sao

After wondering about the huge different in size I did a visual comparison and for me as an average movie watcher the hevc-aq encode looked just like the others. But I wanted to have numbers so I ran a VMAF (vmaf_float_v0.6.1) comparison:
  • x265: 97.520868
  • x265 deblock=-1,-1: 97.541947
  • x265 hevc-aq: 96.264475
  • x265 hevc-aq, CRF 18: 97.296966
(I did an additonal encode with CRF 18 for hevc-aq. All other encodes are still CRF 20)

As far as I understand VMAF, these are all really good results. Too good be the true. I mean it's less than 40% of the size/bitrate of the other encodes and still maintains a really high quality.
Is there something I'm missing here? Known caveats I didn't notice with my test encode? ...
I understand that there is no magic setting that makes all movies look great. Even though I'm currently wondering if I should use hevc-aq to encode my library or not?

Out of curiousity I encoded the whole movie with the different settings:
  • x265: 6311 Kbit/s (5054 MB)
  • x265 deblock=-1,-1: 6188 Kbit/s (5055 MB)
  • x265 hevc-aq: 1846 Kbit/s (1508 MB)

Last edited by burban; 12th March 2021 at 23:14.
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Old 13th March 2021, 01:55   #2  |  Link
benwaggoner
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VMAF has been demonstrated to be poor at discriminating between subjective quality of adaptive quantization algorithms. You'd need to look at the samples to really know if the predictions have a good subjective correlation.
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Old 13th March 2021, 08:27   #3  |  Link
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If I remember correctly, hevc-aq removes quite a lot of details at least at the same CRF level. The reduction in bitrate is most likely a consequence.
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Old 13th March 2021, 11:55   #4  |  Link
burban
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Quote:
Originally Posted by benwaggoner View Post
VMAF has been demonstrated to be poor at discriminating between subjective quality of adaptive quantization algorithms. You'd need to look at the samples to really know if the predictions have a good subjective correlation.
Mhh, ok. I guess PSNR or SSIM are not useful, too? I'm really bad a subjective comparsion.

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If I remember correctly, hevc-aq removes quite a lot of details at least at the same CRF level. The reduction in bitrate is most likely a consequence.
Well there is definetly a loss of detail on the plants on the right and on the brown shirt, but nothing that looks like a 60% decrease in bitrate. While playback I didn't really notice a difference.

CRF 20, AQ-Mode 2:


CRF 20, HEVC-AQ:

Last edited by burban; 13th March 2021 at 12:06.
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Old 14th March 2021, 03:25   #5  |  Link
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If you're encoding your own backup copies to make it easier, then the goal should be acceptable quality loss for size. If you can not see the difference, then that is literally all that matters, as you still have the originals on disc. That's my personal opinion on making a backup that is easier to stream throughout the house/cellphones/tablets. If you're going to backup everything and put it on a Plex/Emby/Jellyfin server, you can remux it and take up lots of space and have the server re-encode it every single time, or you can shrink them down with "acceptable quality loss" in an optimized format to make viewing easier.

In the end, all that matters is what is acceptable to you, as you will be the one watching them.
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Old 15th March 2021, 09:55   #6  |  Link
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You can see the difference in the clouds and also in sharp edges.
If you take a close look at the top left portion of the screen, for instance, you can see a little bit of ringing when AQ is turned on, but most importantly, as soon as you get away from the edge and closer to the sky, the algorithm assumes that it's uniform and removes the original grain pattern:



If we use the subtract function, we can see what AQ got rid off and we can easily see the grain pattern and also some sharp edges around the two main characters:



Now, the reason why I'm telling you this is only 'cause you asked if AQ is production ready and hence my reply would be "no, I wouldn't use it the way it is for our customers", but let's be realistic here, we're not talking about high bitrate masterfiles being encoded for millions of VOD customers, we're talking about a user ripping UHD-BDs and re-encoding them for his personal archive to save space, so... you know what, if they look ok and worth it to you, it's fine as you're the only one who's gonna watch them + family and friends eventually, so it's fine. Objectively we can tell you what it does, but ultimately it's up to you.

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If you're encoding your own backup copies to make it easier, then the goal should be acceptable quality loss for size. If you can not see the difference, then that is literally all that matters
Precisely. It's his own personal backup, so if they're good for him, it's fine.
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Old 15th March 2021, 17:24   #7  |  Link
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Yeah, optimal settings for a mezzanine are very different than for distribution.

Comparing AQ modes at different bitrates is also pretty fraught. I recommend comparing using 2-pass VBR, so you compare the same ABR and source with different AQ parameters. Maybe hevc-aq can give you the same quality at 20% lower bitrate, even if there are some regressions at less than half the bitrate. Could be that --hevc-aq means you can raise CRF by 2 or something.
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Old 19th March 2021, 04:44   #8  |  Link
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Quote:
Originally Posted by FranceBB View Post
Now, the reason why I'm telling you this is only 'cause you asked if AQ is production ready and hence my reply would be "no, I wouldn't use it the way it is for our customers", but let's be realistic here, we're not talking about high bitrate masterfiles being encoded for millions of VOD customers, we're talking about a user ripping UHD-BDs and re-encoding them for his personal archive to save space, so... you know what, if they look ok and worth it to you, it's fine as you're the only one who's gonna watch them + family and friends eventually, so it's fine. Objectively we can tell you what it does, but ultimately it's up to you.
Yep, you're totally right. I guess I will just encode a few movies and watch them completly in order to check for any anomalies. It was just hard for me to find information apart from "it's experimental. don't use it". I understand that it heavily depends on the use case, but I'll give it a try.
As benwaggoner suggested I'll experiment with CRF values a bit further. CRF18 with AQ on still reduces the file size by about 33% compared to CRF20 w/o AQ on my sample. If I really encode my whole 700+ disc collection that will be a significant storage saver.

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Comparing AQ modes at different bitrates is also pretty fraught. I recommend comparing using 2-pass VBR, so you compare the same ABR and source with different AQ parameters.
Alright, thanks for the clarification. I'll try 2-pass VBR encodes as soon as I got a bit of free time :-)
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Old 5th February 2024, 13:51   #9  |  Link
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Any update about this topic?
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Old 6th February 2024, 00:00   #10  |  Link
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Yes, what was being developed as --hevc-aq was completed as --aq-mode 4. Don't ever use the old version!
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Old 15th February 2024, 13:46   #11  |  Link
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Yes, what was being developed as --hevc-aq was completed as --aq-mode 4. Don't ever use the old version!
Translated: forget about hevc-aq?

I am curious anyway about the differences and case use of the 3,4,5 mode. I am currently using aq-mode 5 because it seems the "most complete" but do you have any suggestion about anime vs live action, grainy vs clean, fast motion vs slow motion to apply one of them?
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Old 15th February 2024, 20:26   #12  |  Link
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Quote:
Originally Posted by tormento View Post
Translated: forget about hevc-aq?
Correct.

Quote:
I am curious anyway about the differences and case use of the 3,4,5 mode. I am currently using aq-mode 5 because it seems the "most complete" but do you have any suggestion about anime vs live action, grainy vs clean, fast motion vs slow motion to apply one of them?
3 is just 2 with a bias for lower QPs in darker portions of the video. This can help shadow quality in 8-bit SDR, but also can increase ABR with CRF quite a bit. It's much less needed for 10-bit, and should not be used for HDR, as PQ fixes the issue by having a lot more code values near black.

4 is probably better overall than the others, and benefits from a slightly lower --aq-strength in general. I've found grainy HDR can be better with 2.

5 isn't in MCW x265, so that'll depend on which build you're using and what it does there.
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Old 15th February 2024, 20:48   #13  |  Link
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5 isn't in MCW x265, so that'll depend on which build you're using and what it does there.
I always use Patmanís ones as they are so stable and platform optimized. Do you mind to have a look at its aq-mode?

What mode would you use with anime?
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Old 16th February 2024, 19:13   #14  |  Link
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The thing several peoples said, it's to not use edge-biased (5 & 3 if not mistaken) with HDR. If not already, maybe you can try/test my build with auto-aq.
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Old 16th February 2024, 22:14   #15  |  Link
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The thing several peoples said, it's to not use edge-biased (5 & 3 if not mistaken) with HDR. If not already, maybe you can try/test my build with auto-aq.
in MCW x265, 3 isn't edge based in any way that 2 isn't. The difference is using lower QPs in darker regions.
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Old 16th February 2024, 22:22   #16  |  Link
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The thing several peoples said, it's to not use edge-biased (5 & 3 if not mistaken) with HDR. If not already, maybe you can try/test my build with auto-aq.
I should. Do you have a Mac Silicon build?
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Old 17th February 2024, 12:17   #17  |  Link
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I don't have a Mac and absolutely no knowledge on it...
But the code is on my github to build for those who know how to build for Mac.

Sorry, mistake/mix on specific term.
What i wanted to say it's indeed that several peoples said to not use on HDR a mode "with bias to dark scene", so 3 and 5.
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Old 18th February 2024, 05:24   #18  |  Link
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I don't have a Mac and absolutely no knowledge on it...
But the code is on my github to build for those who know how to build for Mac.
No worried. I'm off to HPA tomorrow with just a Mac, but I can check it out on a Windows system a week later.
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Old 18th February 2024, 11:13   #19  |  Link
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My advise would be to try auto-aq with hysteresis (i add the hysteresis to avoid a possible risk), and if for HDR, enable the HDR mode, so "--auto-aq 6" (bits 1 & 2 set to 1).
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Old 18th February 2024, 13:42   #20  |  Link
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The thing several peoples said, it's to not use edge-biased (5 & 3 if not mistaken) with HDR. If not already, maybe you can try/test my build with auto-aq.
Edge biased are good to use, but luma biased ones are not (because they are pretty much counterproductive to --hdr10-opt). So modes 3 and 5 should not be used and as you mentioned, the auto mode 6 is the one for HDR.
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