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29th July 2007, 20:58 | #21 | Link | |
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SSIM is a much better indicator than PSNR. What you have to take into account in addition to SSIM is primarily the fact that one bad area of an image, or one bad area of a video, is a lot worse than slightly reducing the quality of everything else. This is the problem with highly optimizing video encoders; they may decide that creating an ugly block here would save enough bitrate to increase the quality a lot more over there. But what we see is the ugly block. |
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29th July 2007, 21:23 | #22 | Link | |
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Obs: I'm running MSU application [ Blocking (MPEG-4) Beta comparison ] to see if my eyes/brain agree with that. It's very time consuming (on Intel 6600 2.4GHz dual-core at 70% cpus utilization). |
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29th July 2007, 21:36 | #23 | Link | |
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Actually, an idea just struck me: add a new feature to x264 that does the following; it wouldn't be hard (it would be an optional commandline of course): Commandline: --qf --qf-threshold Variables: block-width, block-height Quality Fixer does the following: 1. At the end of encoding an area of the frame equivalent to a block of block-width and block-height, QF is activated. 2. QF does SSIM on the block. If SSIM is less than qf-threshold, it estimates how many more bits are needed to get the quality equal to or above qf-threshold. 3. In the case that SSIM is less than the threshold, the block is re-encoded with a newly estimated quantizer. 4. (Possibly) repeat process until SSIM is above threshold. 5. (Possibly) do the above if SSIM is a lot above the threshold in order to lower the SSIM and save bits. In other words, find the area of the frame where lots of bits are being wasted and fix that. It would be time-consuming, but it could provide a visually optimum result. It could even be a new ratecontrol option: not only would it provide a target SSIM, but it would also provide an equal SSIM in all portions of the frame. Last edited by Dark Shikari; 29th July 2007 at 21:41. |
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29th July 2007, 22:29 | #24 | Link | ||
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Actually, all those options are important. I mentioned custom matrices in the first place, because the default quantization tend to block. Try looking for the "Prestige CQM". One thing I forgot to mention, that should also be on the list (Very High, maybe like no.4 or 5), is the deadzone options. This affects grain retention. Last edited by Terranigma; 29th July 2007 at 22:35. |
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29th July 2007, 22:35 | #25 | Link | |
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AQ still requires custom, as you surmise. When you reordered the list, lower values should be higher on it than higher. (ie, subme 6 is more important than subme 7, as it provides more benefit compared to the amount of extra time it requires than 7. 7 still provides more absolute benefit, of course. Trellis and reference frames are the same way.) In fact some time ago, someone posted a comparison of most of the options with speed hit and quality gain listed, ordered by the ratio of the two; might have been manao or akupenguin. |
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29th July 2007, 22:42 | #26 | Link | |
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Le Sagittaire ... ;-) 1- Ateme AVC or x264 2- VP7 or RV10 only for anime 3- XviD, DivX or WMV9 |
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29th July 2007, 23:30 | #27 | Link | |
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just to be complete, here's my current preferred setting: Code:
--crf 20.0 --level 3 --keyint 100 --min-keyint 1 --ref 3 --mixed-refs --no-fast-pskip --bframes 2 --b-pyramid --bime --weightb --filter -2,-2 --analyse p8x8,b8x8,i4x4,i8x8 --8x8dct --vbv-bufsize 1835 --vbv-maxrate 10000 --threads auto --thread-input --progress --no-dct-decimate --no-psnr --no-ssim --output "" --aq-strength 0.9 beware, i optimize my settings for a good overall "look" and a balanced encoding speed, not for maximum compression or good metrics. |
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29th July 2007, 23:32 | #28 | Link |
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Oh, I must warn you. Never use trellis 2 for 2-pass encoding (At least for the first pass anyways). Doing so would surely cause an erratic behavior; corrupting your encode in the end
e.g. Presenting blocks where it should'nt be present, not using a high enough bitrate for certain frames, etc... Only use trellis 2 for the final pass. You can, however, safely use trellis-1 without any noticeable side effects as you would if you use trellis 2 for the passes where it gathers stats. |
30th July 2007, 01:47 | #29 | Link | |
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Yes, it is. Well, it was now: Very clear/helpful picture. So --partitions equals -- analyse. OK got it.
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30th July 2007, 02:00 | #30 | Link | |
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3) In multipass encode, I understand there is a kind of "intelligence" in the encoder to choose where to compress more and where to compress less. Is this "intelligence" free to the programmer to choose ? (example: could be possible to analyze luminance in each frame and if dark, compress much less ?) The difference I was looking to encode based on luminance and you propose based on SSIM. I still have a problem with SSIM or I am still trying to understand SSIM, but it sounds a great idea to me: give us some control of the "intelligence". |
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30th July 2007, 02:15 | #31 | Link | |
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- "for the same frame ..." - "you can not compare diff frames ..." Ok, but in the end we will be comparing different frames because that is what video is: sequence of different frames. Back in my example: If I have a sample with 2 frames and PSNRs are 35 and 45, and I apply a parm that give me now 39 and 39, what can I say ? Let's assume for example, the first frame with 35 was visually bad and now with 39 became good and the 2nd frame with 45 was good and now with 39 it is still good (sure not as good as 45, but still visually good). I will say that parm I applied increased the quality despite the mean PSNR became reduced. |
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30th July 2007, 02:22 | #32 | Link |
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entropy encoding (cabac) only enhanced compression, not affect to IQ.
I think that is impossible determinate. You only can compare the same frame. Its posible that now the 2nd frame with 39 are so bad that the old 1st 35, or maybe 1st frame with 39 dont have enought IQ. Differents frames different IQ. Last edited by Theliel; 30th July 2007 at 02:30. |
30th July 2007, 02:31 | #33 | Link |
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And because of that, it saves a ton on the bitrate (Now i'm sounding a bit like the slogan for the geico auto insurance). This's why I chosed it as the most important factor, but this's just my opinion. h.264 is meant for high compression wasn't it, or am i'm wrong in thinking that?
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30th July 2007, 02:41 | #34 | Link |
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of course
i said this because i belive that MarcioAB want search only the IQ parameters "Importance in Quality (no care about time or size)". of course, if cabac save up arround 30% in size, you always can increase the bitrate and increase the IQ |
30th July 2007, 02:48 | #35 | Link | |
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If I encode a source keeping the same bitrate (of filesize) and set CABAC in the 1st and not set CABAC in the 2nd, I guess IQ will be better in the 1st than the 2nd. Is that true ? Maybe I should say the list is for "no care of time encode" but keeping the same bitrate. EDIT: Read your 2nd post now. Correct: Definitively must adjust the context of the list. Last edited by MarcioAB; 30th July 2007 at 02:50. Reason: in the body |
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30th July 2007, 03:06 | #36 | Link | |
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Its possible that now the 2nd frame with 39 are so bad ... Yes, but it is also possible that the large drop in the 2nd frame, from 45 to 35 may still generate a good visual quality to me (or IQ). That is my problem with SSIM and PSNR. I know we need numbers to compare, personal opinion is too much subjective, check frame by frame is boring and that I just did it in 3 medium size samples, but all of them indicated me such discrepancies regard my concept of bad image quality versus SSIM and PSNR. I can judge much more easily bad frames than the good ones. Last edited by MarcioAB; 30th July 2007 at 03:09. |
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30th July 2007, 09:13 | #37 | Link | |
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PSNR work good if you know how work PSNR. If you use CQM, AQ or other HVS setting then PSNR can't help. If you change only internal search for x264 (ME, RDO ... ect) then better OPSNR mean generaly better quality for eyes.
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Le Sagittaire ... ;-) 1- Ateme AVC or x264 2- VP7 or RV10 only for anime 3- XviD, DivX or WMV9 Last edited by Sagittaire; 30th July 2007 at 09:20. |
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30th July 2007, 20:43 | #38 | Link | |
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Recommended all-in-one stop for x264/GCC needs on Windows: Komisar x264 builds! |
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2nd August 2007, 02:08 | #39 | Link | |||
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Ok.
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If I understood well, OPSNR treat the entire video as a single picture. I wonder how a single number can be so meaningful for 200000 frames, but ok, let me respect that and use it as an auxiliary indicator. After each PSNR "judgment", I tend to go to the "crime scene" and check. My perception (IMO) is that PSNR can see well "blurry" and "color shift" parts, but it is blind to "blocky". To my taste, "blocky" is the worst part, followed by "blurry" and almost no care about "color shift". Quote:
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Thank you. |
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2nd August 2007, 02:23 | #40 | Link | ||
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Thank you |
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