CQ vs. CQ_VBR ... VERY INTERESTING...
Hi kwag and others...
Last night I ran a couple of tests with bitrate viewer... I used the file size prediction clip from Frequency, which I want to put on one 80 min. CD-R. I used the new GOP structure and Blockbuster 0.6 together w/ FluxSmooth. I resized it with Avisynth Bilinear resize to the resolution 704x576 (PAL). I also masked the borders in TMPGEnc. Sample #1 : The first sample I did with the old KVCDx2 704x576 Template with the Default Matrix using the new GOP of 1,12,2,1,24 and I set the CQ Level to 57... File Came Out At : 11,391 KB Sample#2 : The second sample I did with the KVCDx2 PLUS Template for PAL using KVCD Matrix together with the new GOP, and CQ_VBR. I had to lower the CQ_VBR level to 5,98 to get the same size... File Came Out At : 11,374 KB Now here comes the thing I don't understand... Viewed w/ WMP I already saw that the KVCDx2PLUS Template was of less quality than the first sample. Viewed with bitrate viewer the Average Bitrate was 891 for both samples. But... Sample #1 had an average Q-Level of 5.28 , Sample#2 had one of 6.55 ... Now that's a hell of a lot difference... 8O Did I do something wrong?? |
Hi jellygoose,
No you didn't do anything wrong. Maybe it's time to look again at CQ :idea: Last time I did this was at TMPEG version 2.50 or so, so maybe there is a difference now with CQ. Originally CQ_VBR was better quality than CQ for the same file size. Maybe it's time to review this. Also, before we didn't have prediction, so it was hard to target a file size. I'll do some tests to verify your findings. Mind you, I recall some people had problems playing KVCD encoded as CQ, but not as CQ_VBR 8O . So the data on the stream has a different pattern from CQ to CQ_VBR. This you can see clearly in Bitrate Viewer. -kwag |
Running my first test now...
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Happy Testing... |
Resident Evil, 1h35m, 352x480
CQ_VBR 15.63: avg. Q = 2.12, peak Q = 5.92, size = 11,890,602 P spoilage 0, B spoilage 10 Closest Q level: CQ 73, avg. Q = 2.36, peak Q = 3.80, size = 11,429,682 Closest size: CQ 74, avg. Q = 1.84, peak Q = 3.63, size = 11,669,852 P spoilage 5, B spoilage 20 Closest Q level: CQ 77, avg. Q = 2.34, peak Q = 3.75, size = 11,650,255 Closest size: CQ 78, avg. Q = 1.84, peak Q = 3.59, size = 12,038,198 P spoilage 0, B spoilage 0 Closest Q level: CQ 70, avg. Q = 1.85, peak Q = 3.50, size = 10,423,978 Closest size: CQ 71, avg. Q = 1.86, peak Q = 3.63, size = 11,547,443 Observations - CQ mode seems to be non-linear between integers, i.e. 73.9 is closer to 73 than to 74. - P- and B-frame spoilage of 0 provides significant reduction in both Q level and file size, at least at this resolution. I'm now going to run some "subjective quality" tests. |
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Now maybe we can even tune B and P spoilage with CQ IF CQ does provide better quality on the same space as CQ_VBR :idea: -kwag |
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Seems that CQ mode is more aggressive than CQ_VBR. I'm now testing with more noise. |
When you increase the noise to try to compensate for the blockiness, things start to look very bad very quickly.
Based on the tests I've done so far I would say that CQ_VBR provides significantly better subjective quality than CQ for a given bitrate, despite the lower Q level as reported by BitRate Viewer. So it seems the Q level, while generally a good indicator of relative quality, should not be relied upon without a side-by-side inspection of the two encodes. |
Here are my test results:
Test #1 CQ_VBR: file size= 11,717KB http://www.digitalfaq.com/archives/i.../2002/12/3.jpg Test #1 CQ: file size= 11,517KB http://www.digitalfaq.com/archives/i.../2002/12/4.jpg I can see almost no artifacts on the CQ sample. They are clearly more visible on the CQ_VBR sample. Here are the samples. See for yourselves: http://www.kvcd.net/test-cq-vbr.m1v http://www.kvcd.net/test-cq.m1v <-------- Winner or not :?: 8O Script used: LoadPlugin("C:\encoding\MPEG2DEC.dll") LoadPlugin("C:\encoding\fluxsmooth.dll") LoadPlugin("C:\encoding\sampler.dll") LoadPlugin("C:\encoding\blockbuster.dll") LoadPlugin("C:\encoding\legalclip.dll") mpeg2source("K:\K19\VIDEO_TS\k19.d2v") LegalClip() BilinearResize(672,336,0,0,720,480) FluxSmooth() Blockbuster( method="noise", detail_min=1, detail_max=10, variance=.5, seed=1 ) AddBorders(16,72,16,72) LegalClip() #sampler() So, what's next :?: :?: :?: -kwag |
That's exactly what I see kwag...
SansGrip: You're right, DCT Blocks don't disappear completely w/ blockbuster and CQ but... With CQ_VBR there are a lot more visible artifacts, especially around movements in the background... as far as my bad eyes can see... Take a look at kwags samples, they show the exact same results that I have... |
:o I just took another look at kwags script again. How come you're using a variance of 5 for the blockbuster filter? is that the default setting?
Another question: How come bitrate viewer tells me my VBV Buffer was 20, when I encoded with a value of 40 ? |
Here's another view. Please pay special attention to the water and fire scenes:
These are shorter samples: http://www.kvcd.net/k19-cq-vbr.m1v http://www.kvcd.net/k19-cq.m1v -kwag |
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-kwag |
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Hi Kwag,
Kwag wrote: Quote:
It's been some time since I encoded a 704x480, but this could be another discovery. The fire scene was much better in the CQ clip and other scenes were the same as CQ_VBR to me. This is worth looking into. :) Someone correct me if I'm wrong but the file prediction formula for CQ is more of a linear formula than CQ_VBR :?: -black prince |
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The samples I posted above, that's the way the complete movie would fit on one CD at 704x480 8O, so at 528x480 it should be even better. And I like that :mrgreen: -kwag |
kwag's clips definitely show the opposite result to my test. kwag, I think if you try it at 352x480 you'll notice much worse DCT blocks in the CQ version. If anyone wants I can do another couple of strips and post them for people to see.
Looking at the first clips you posted from K19, the CQ version is much better. What I do to compare clips is use VirtualDub to "fast recompress" them using Huffy (this takes a lot of disk space, but is lossless). Then I use a script like this: Code:
clip1 = AviSource("test-cq-vbr.avi") http://www.digitalfaq.com/archives/error.gif Look at the chrome on the top/side of the car, and at the window in the bottom-left corner of the frame, and the wall in the top-right corner. The CQ version is obviously a lot better at this resolution... |
Note: I just realized that the samples I encoded above were all done with "High quality" and not "Fast" on motion estimation in TMPEG.
And that takes a LOOOOOOONG time to encode. But if it makes a hell of a difference in quality, I WILL wait for longer encodes if I can get the best quality. I have to try again with "Fast" motion estimation and see if there's any visual difference between CQ and CQ_VBR. On "High quality" estimation, obviously there is a difference. -kwag |
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I have to dig more into AviSynth scripting 8) -kwag |
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-kwag |
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Right now I'm figuring out a good CQ_VBR for R.E. at 704x480, 1 disc. Then I'll try to get as close to that size as I can with CQ... |
Anyone else noticed that sometimes several CQ values (in my case 52-54) produce almost identical file sizes?
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-kwag |
So how will using CQ instead of CQ_VBR affect the prediction? Will KVCDP be able to be used the same way or do we have to do manual prediction?
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I just found correct sample sizes for both CQ_VBR and CQ, but am having mixed results. While one particular frame is much improved with CQ (with CQ_VBR it is almost entirely made up of macroblocks), generally the CQ version is slightly more blocky. But this is with motion estimation -- I'm currently reencoding at high quality to see if it makes a difference. |
I have a feeling that CQ mode has a better bit rate allocation than CQ_VBR. That's why artefacts are less noticeable than with CQ_VBR. That's just my thought :o
-kwag |
@Kwag and SansGrip,
Used 704x480, GOP=1-2-12-1-24, commented Blockbuster noise, 2 CD's with 112kb audio and CQ=85. The movie, Vanilla Sky, 2hr 19 min and the verdict is WOW great 8O Looking at BitRate Viewer, the average Q = 2.87. I wish there was a corrulation between picture quality and Q. :? Fast action scenes has the lowest Gibbs noise I've seen, even better than KVCDx3 (528x480). This template seemed more compressable the the PLUS templates. I going to try this same resolution for 1 CD. :D I too would like to know what file prediction formula should be using for this :?: -black prince |
As a side note:
CQ_VBR 6.5 (motion estimation) = 11,910,158 CQ_VBR 6.5 (high quality) = 10,610,730 Edit: Also: CQ 56 (motion estimation) = 11,796,690 CQ 56 (high quality) = 11,303,978 Haven't done a visual compare of them yet... |
http://www.digitalfaq.com/archives/error.gif
http://www.digitalfaq.com/archives/error.gif I think I'll let the pictures speak for themselves :). |
So how will using CQ instead of CQ_VBR affect the prediction? Will KVCDP be able to be used the same way or do we have to do manual prediction?
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I currently started to encode "K-19" at 352x240 LBR just to test the formula on CQ. It should be the same. Let's see how far off is the final target to the predicted size. I'll post result here when it's done. In about 2 hours. -kwag |
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Ah, kwag, there you are -- I thought you'd gone missing ;). What... spending time with the family on Christmas Eve instead of TESTING? :mrgreen:
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-kwag |
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