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17th October 2020, 23:20 | #1 | Link |
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What happened to --auto-aq ?
In February there was a nice patch about a new parameter --auto-aq, which automatically decides the AQ Mode (2, 3, 4 or 5) for each frame using its scene statistics.
https://mailman.videolan.org/piperma...ry/012882.html But this patch never made it into master. Does anybody know more why they did not pursue on that idea? I quite liked that idea, so I made myself a customized version of HandBrake, that includes this patch. And it gives me nice results, good quality and much smaller files size. So, I don't really understand why this patch never made it into master. |
19th October 2020, 17:23 | #2 | Link | |
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I can imagine it is a difficult feature to avoid thresholding issues with. For example, if the aq-mode changes mid-shot, that could be quite jarring. It likely wouldn't happen much with most content, or with long GOPs such that there aren't many mid-shot IDRs. But with content that varies a lot in style (like mixed CGI/cel/live action) there could be some challenges. And that's exactly the content where changing aq-mode would be most valuable. With an analysis pass or long lookahead these could be addressed, but it strikes me as a finicky feature. Plus, does it auto vary --aq-strength too? Because the same value might not be optimal in different modes. That likely would need some auto-adaption as well. And there simply aren't any objective metrics that do a good job of comparing adaptive quantization modes anyway. Even VMAF gives very similar scores for different approaches, and sometimes penalizes the subjectively preferable mode. I suspect Netflix didn't include a lot of aq-mode variation in their subjective rating database, so VMAF didn't get trained on those variations. Machine Learning/AI is only as good as the training set, and isn't good at finding types of differences it hasn't been exposed to. |
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14th December 2020, 22:33 | #4 | Link |
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I thought, maybe more people want to test --auto-aq and experiment with it. Therefore I made some versions of HandBrake that include a patched version of x265 to enable --auto-aq. The executables are for Windows and macOS.
You can find them on this very basic (didn't put much effort in it, I know) download page: https://polysom.verilite.de/handbrake/handbrake.html There must be a reason why they didn't follow up on this patch, so use --auto-aq only for testing purposes. I need to say, that I don't own a Windows machine, so the Windows executables are completely untested and I can't build a GUI version for Windows. I only tested the macOS executables. There is also one issue, I found with --auto-aq. Even if --auto-aq is enabled and --auto-aq does show up in MediaInfo, it does say --aq-mode=2. But I think it should be --aq-mode=auto, shouldn't it? |
21st December 2020, 09:56 | #5 | Link |
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x265 has been entirely in a maintenance mode for at least a couple of years. The only big features that get in are sponsored by streaming companies now, there's no budget or will to review and tweak something as wide-reaching as this patch. Maybe if there's a significant groundswell it might help, so your builds are a big deal!
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21st December 2020, 23:06 | #6 | Link | |
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Edit: d'oh, this was from before the HG to git migration wasn't it? Last edited by Greenhorn; 22nd December 2020 at 07:05. |
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25th December 2020, 18:59 | #7 | Link | |
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Edit: I've uploaded the unbitrotted combined patch I've used here: https://github.com/Nomis101/x265/com...b1e3bb147fa0ff Last edited by ShortKatz; 26th December 2020 at 18:38. |
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28th December 2020, 22:53 | #8 | Link |
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Is there any reason to think this older algorithm would be beneficial in current builds? Other changes around AQ stuff likely would require auto-aq changes. I believe it predates --hevc-aq, among other things.
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29th December 2020, 00:00 | #9 | Link |
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I don't know how useful --auto-aq itself will be (it's just using simplistic statistics to determine which aq mode to use), but the patch itself is from this year (hevc-aq was added in ... 2018 I think?), and additionally includes another aq-mode (5) which is mode 4 with a dark-scene bias. IMHO that's the really interesting part of it.
Last edited by Greenhorn; 29th December 2020 at 01:10. |
6th January 2021, 02:22 | #10 | Link | |
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