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Old 2nd September 2008, 14:43   #1  |  Link
Inventive Software
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x264 - the state of play at the moment

I've been following development of x264 for the past few months without using it on a regular basis. I now have need to use it for transcoding VHS>DVD backup to H.264. There is one slight problem. The "Current patches...." thread has really confused things for me, and all the patches flying around at the moment are completely screwing with my head with regard to what's good, what doesn't work, what's completely broken, and what goes against all advice but still comes out on top.

As I understand it, Dark Shikari has a few patches in limbo (not completely finished, but he'd like them in the trunk) at the moment:
  • VAQ2
  • PsyRDO
  • PsyTrellis
  • New B-Frame decision

Correct me if I'm wrong, but this is how I follow things.

VAQ2 I was following based on the amazing picture quality of VAQ1, which eventually made it into the GIT trunk. PsyRDO has helped reached a level of confusion with people applying various patches to vanilla x264 builds that appear to clash with their intended operation, and from memory, VAQ2 is deprecated based on PsyRDO. PsyTrellis is a new-fangled motion helping bring more quality to various settings, and completely screwing the metrics over. The new B-Frame decision mode appears to have big speed issues, but is much better with regard to *most* content.

I'll say it now: those who use metrics to try and prove something with PsyRDO and PsyTrellis are wasting their time. "Psy" is short for "Psychovisual", very loosely meaning screw with the head via the eyes. People would do well to quote and say "Amen" to get the bloody message across!

I realise there are probably a few major bugfixes to make it into the GIT trunk in the short term, but what I'm asking is: what's a good build that I can archive stuff with? Ordinarily I'd use the x264.nl Sharktooth links to in "his" post, but the PsyRDO and PsyTrellis patches have me interested!
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Old 2nd September 2008, 15:05   #2  |  Link
burfadel
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Isn't the PsyRDO and PsyTrellis part of the same patch?
Anyways, I guess the patches to choose are the ones that give the best subjective quality/file size for your intended purpose. The new b-frame decision patch and the psyrdo/trellis one are both good, just stick with 5 b-frames using the command line option --b-adapt 2

Trellis has to be set to either 1 or 2 for psytrellis to work (which kind of makes sense), although 2 would be a much better option that 1, especially considering a bugfix made to trellis 2 in a very recent build (the bugfix slows down encoding but gives better quality than before). Psyrdo requires a subme or 6 or greater, and works best with --b-rdo (makes sense also).

The easiest thing to do is try the rev 956 mod build as on the x264.nl homepage, all the useful x264 builds are very similar, but its great to have the choice! Ranguvar's, bobor's, skystrife's, x264.tk (and no doubt I'm missing a few) all make good builds, its kind of a matter of choosing the latest one with the patches that you want in them! sometimes they may omit certain patches for certain builds.

I wouldn't worry about using matrices files, x264 does a very good job, and they become redundant really when considering AQ, psytrellis, psyrdo etc etc. The b-frame decision patch is probably the one that needs the most work on it, in terms of performance and some anomalies, the others seem pretty good. They may just require a bit of final refining and testing before being committed. The target is to not introduce new bugs in to the official git, not to play catchup later!

Last edited by burfadel; 2nd September 2008 at 15:09.
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Old 2nd September 2008, 16:54   #3  |  Link
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He did not mean "matrices", as in custom quantization matrices, he meant "metrics" (SSIM and PSNR, among others) which are ways of roughly assigning a numerical value to encode quality. Useful for doing quick testing of patches and stuff, but useless for most "real" stuff.
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Old 2nd September 2008, 17:02   #4  |  Link
Sharktooth
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most ppl confuse how metrics work and what metrics are. metrics measure differencies from the original image... that's completely different from quality. assuming metrics measure quality, is a big mistake.
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Old 2nd September 2008, 17:06   #5  |  Link
wyti
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No it's true if you disable all kind of psy optim.
Without psy optim the goal of a codec is to be as identical as possible from the source, and metric show us that.
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Old 2nd September 2008, 17:10   #6  |  Link
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Quote:
Originally Posted by Sharktooth View Post
most ppl confuse how metrics work and what metrics are. metrics measure differencies from the original image... that's completely different from quality. assuming metrics measure quality, is a big mistake.
True, and I know that. I was just saying what the general usage is, though I probably should've also mentioned what you said.

@wyti: In that case, metrics are more helpful, but still cannot replace a good visual test. Look at AQ, for example.
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