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| stephanV |
| Posted: Aug 28 2005, 06:03 PM |
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| QUOTE | | you cannot do that, my good man, as bpp and average quant. are "bollocks" for you , as you said. |
Well then something else needs to be thought of. 
| QUOTE | | it's kinda catch22 for you, isn't it? you have few theories that this can't work, and yet you can't prove it wrong, so now what will you do? |
The problem is that the experience cannot be brought back to a workable model. Sure you can say q3 always looks good, but what use is it to me? Files turn out too large that way in any case. To drift off a bit, I can always assume something falls down on the ground when I throw it up... until I go into space. So the question is: Is there a "space" for video, and if so, where is it?
To restate the problem: I cant go and encode a video, use a bpp and have a targeted average q as result. Maybe if you make a q range of +/- 1 off the middle. But how useful is that? YMMV i guess...
Being a nihilist it seems.
But that's ok, I'm just one of those people that attaches more value to understanding something than actually using it.
@Frank
| QUOTE | | Another thing: when you use b-frames the std.deviation fails to calculate. |
B-frames are meant to "over"-quantized, meaning they will normally have 1.5 to 2 times the quant value a p-frame would have. B-frames are designed for this purpose and normally have only a small reduction in quality compared to the p-frame that would be encoded, but a high reduction in frame size. Note that this will not only throw off your std, but also your average quant... although I'm not sure how DRF analyzer deals with this.
So now we already need at least to use different values if we want to also accomodate for b-frames. But b-frame behaviour is rather impredictable and depends highly on settings...
| QUOTE | There are options in codec to set the quality of your session with quantizer instead of kb: move slider towards q2 encoding is better and so on...
So what's the problem with this utility assumptions if codecs themselves have this approach to set the quality? |
You only set the quant, not the quality. If a codec calls constant quant constant quality this is rather silly.
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| i4004 |
| Posted: Aug 28 2005, 07:37 PM |
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| QUOTE | | Well then something else needs to be thought of. |
because drfanalyzer said you're mediocre?
we said that "medium"="nice".
for us.
on our tv-outs. on average quant. of 4 on 512x576.
(hehehe..talking about the variables!)
| QUOTE | | If a codec calls constant quant constant quality this is rather silly. |
because akupenguin said..something..somewhere?
constant quant mode indeed is constant quality.
please feel free to prove me wrong.
i think you failed once in this thread (as you said quant3 can look bad), let's see if you can do it again.
please be aware; xvid encoding with b-frames and 5/8 quant(for example) is not constant quant. mode.
| QUOTE | | B-frames are designed for this purpose and normally have only a small reduction in quality compared to the p-frame that would be encoded, but a high reduction in frame size. |
could you tell us what does "high reduction in frame size" means?
how much is the bitrate reduced, and how much is the image spoiled?
(one more tough one, no? )
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| stephanV |
| Posted: Aug 28 2005, 11:12 PM |
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| QUOTE | | (hehehe..talking about the variables!) |
indeed
| QUOTE | | please feel free to prove me wrong. |
I can show you some stuff q3 stuff that actually looks pretty bad relatively speaking (on my monitor (=TFT), dont know about TV). Its a space shuttle in blue air. Its especially bad when watched in motion, dont even try full screen (res of vid is 624x352 BTW). Now you can say codecs do bad on gradients, but if codecs are bad on some stuff and good on other then they cant possibly give you constant quality on constant quant.
| QUOTE | | please be aware; xvid encoding with b-frames and 5/8 quant(for example) is not constant quant. mode. |
Hey, I'm stubborn, not stupid.
| QUOTE | could you tell us what does "high reduction in frame size" means?
how much is the bitrate reduced, and how much is the image spoiled? |
This would depend very much on settings... but ill use XviD with defaults ok?
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| i4004 |
| Posted: Aug 29 2005, 12:35 AM |
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| QUOTE | | but if codecs are bad on some stuff and good on other then they cant possibly give you constant quality on constant quant. |
i wanna see this clip. it was divx, or xvid, right?
one can reason in this way; if that codec will always give same artefacts on same quant on same source, it's constant quality. you may not like that quality, but it's constant.
(we can't change the fact mpeg is lossy, and that it hates some things, so no need to discuss that. we also can't change the fact that divx4/5 and xvid are crap.)
we're playing word games now, but i wanna see the clip. divx and xvid can crap-out on sky like no other (recent) codec. they band quickly, and produce false motion.
| QUOTE | | Hey, I'm stubborn, not stupid. |
plenty people call such enc. cq, i'm afraid, so i was just checking.
| QUOTE | | This would depend very much on settings... but ill use XviD with defaults ok? |
use whatever you want, but pick some tough source from here
http://www.ldv.ei.tum.de/liquid.php?page=70
or here
http://index.apple.com/~singer/sequences/testseq.html
(if you can get them in container you want... )
i mean...you didn't thought i would be interested in re-encoding the dvds?
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| TechMage89 |
| Posted: Aug 29 2005, 03:29 AM |
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Describing CQ as giving constant quality is a bit misleading. Saying it gives constant detail would probably be closer.
After all, what ever sort of (ugly) noise your video had when you encoded it would be included in your definition of "quality."
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| stephanV |
| Posted: Aug 29 2005, 08:48 AM |
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| QUOTE | | i wanna see this clip. it was divx, or xvid, right? |
It was made with that nandub 1-pass tool. I just capped the quants to 3-3 range (which worked pretty well, although it was a bit heavy on the i-frames). If you don't agree with this method, you can suggest other settings. I will look for some space to upload a small clip and post it later on.
| QUOTE | | one can reason in this way; if that codec will always give same artefacts on same quant on same source, it's constant quality. you may not like that quality, but it's constant. |
The point is that the complete video wasn't just the space shuttle in the sky, there were also people talking and that looked far less annoying to me, so I say quality is not constant. But if you are gonna define constant quality with such restrictions, then yes, you are right.
| QUOTE | | i mean...you didn't thought i would be interested in re-encoding the dvds? |
Source is source; you cant make general comments about things if you only are interested in your specific use. But ill pick one of those.
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| frank10 |
| Posted: Aug 29 2005, 10:02 AM |
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Apart from a q3 looking bad or good, it's the theory behind this that we're interested in.
We also don't have so many variables as you said:
Let's say we take a clip and a codec (doesn't matter which one with its weakness) with ffvfw (that has constant Quantizer option), some resolution (doesn't matter which one) and some other settings fixed.
Then we change ONLY the quantizer setting.
Let's say we choose a q4. Then we change it at q3 and so on...
Which final clip will be better (or will have a better quality, detail, look, psicovisual-acustic appearance   ).
For sure it's not the better compression efficiency in filesizes but here we're talking about quality (Can we use this word? )
I mean if frameX in this clip has a q4, how can that same frame be better with the same settings-codec? Only with a q3 or q2. Simple. And that is linked with a gain in kbs (as you said earlier this gains quality).
So it seems to me that generally speaking different analysys of the same clip tweaked several times to gain lower average-std dev makes sense and the one with the lower q will look better.
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| stephanV |
| Posted: Aug 29 2005, 10:35 AM |
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clip is here --> http://www.savefile.com/files/6087410 (0.5 MB)
| QUOTE | | Let's say we choose a q4. Then we change it at q3 and so on... |
I never argued that for the SAME source q4 was better than q3. My argument is about two things:
1. While for the SAME source q3 is better than q4 (or definitely not worse), it doesn't necessarily mean q3 looks good. There is big difference in concept between 'better <-> worse' and 'good <-> bad'.
2. When different sources are compared, it might be that q4 vid is better than the q3 vid. (The clip I posted above looks pretty poor in my opinion and I can show you other clips at q4 that are more acceptable to watch then that.)
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| i4004 |
| Posted: Aug 29 2005, 02:17 PM |
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techmage, sod off.
stephan; load this clip straight to vdub(i used 1410), and hit 'play input'. now rewind and hit 'play output'. now load via dshowsource (ffdshow decoding) and hit 'play output'.
you know, i was also recently tinkering with gradient (because i run into this ).
it's a colorspace limitation(namely, output colorspace limitation, as you saw different playback methods change things).
get this;
http://i4004.net/i4004/gradient/imagereader_3.m2v
load to vdub-mpeg2. how does it look?
play in (for example) windvd or with elecard. how does it look?
certainly not.
if you use dvd as a source, then you're just recompressing the already smoothed video.
it is already smoothed for 2 reasons:
-it is a film source
-it passed one compression already
use something sharp that video camera produced.
or something that was artificially produced and has sharp edges etc. (graphics ..you know, the stuff that rings )
| QUOTE | | 2. When different sources are compared, it might be that q4 vid is better than the q3 vid. (The clip I posted above looks pretty poor in my opinion and I can show you other clips at q4 that are more acceptable to watch then that.) |
wohoo..wait; you'll be comparing different quants on different sources?
what will that tell us?
talking about taking things too far.
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| stephanV |
| Posted: Aug 29 2005, 03:36 PM |
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| QUOTE | | it's a colorspace limitation(namely, output colorspace limitation, as you saw different playback methods change things). |
Partly, since different codecs behave differently on this (ffvfw seems to have less banding). In any case, its highly annoying. Some guy from ateme said it was because codecs all optimize for PSNR and it is this what causes it... we'll see if it ever gets better though.
| QUOTE | wohoo..wait; you'll be comparing different quants on different sources?
what will that tell us? |
Exactly what I have been trying to tell you: constant quant is not constant quality. Constant quality is not: "quality changes every time there is a scene change"
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| i4004 |
| Posted: Aug 29 2005, 05:02 PM |
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| QUOTE | | we'll see if it ever gets better though. |
as soon as luma and chroma planes get to be 16bit.
that should give it enuff levels.
(i just laughed at our priv. forum how zx-spectrum was 8-bit.)
but i would say this is a rare problem. i'm not complaining.
cquant is constant quality in the mpeg context.
offcourse, as you've pointed out here, mpeg context is not the best (or absolute) merit for the reasons you mention.
yes.
i can't say that mpeg is compressing everything equally good. indeed.
but let's focus on the mpeg sequences test. i (still) don't have these sequences (should tell somebody to dload and send them to me) so i'm interested to hear about your attempts to decode these. perhaps a mere yuy2 decoder of huff could do. or ms' (from directx).
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| frank10 |
| Posted: Aug 29 2005, 05:23 PM |
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| QUOTE | I never argued that for the SAME source q4 was better than q3. My argument is about two things:
1. While for the SAME source q3 is better than q4 (or definitely not worse), it doesn't necessarily mean q3 looks good. There is big difference in concept between 'better <-> worse' and 'good <-> bad'.
2. When different sources are compared, it might be that q4 vid is better than the q3 vid. (The clip I posted above looks pretty poor in my opinion and I can show you other clips at q4 that are more acceptable to watch then that.) |
Well, stephanV, both points seem obvious to me: it always depends on the source. For example, if you get a noisy one, how can you compare to a clean one? There's no q (and nothing else) at all!
But i4004 and me were never saying to use this tool this way. I started this thread to ask how to adjust a clip regard the resolution and bpp; then I saw this drfAnalyzer and I thought this could help to find out when you are in the good way to get the best from THAT SAME clip. That doesn't mean of course that clip will look good (it's always a source thing), but that you're getting out the best you can from it. That's all.
At least here we are converging.
I agree someone could be using this util wrong comparing different clips, but they aren't us.
btw: in your shuttle clip DRFanalyzed it could have been some clue on poor quality because of bpp with the relative warning... |
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| stephanV |
| Posted: Aug 29 2005, 06:49 PM |
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@ivo:
| QUOTE | | i can't say that mpeg is compressing everything equally good. indeed. |
I'm glad we have some sort of understanding then.
| QUOTE | | but let's focus on the mpeg sequences test. i (still) don't have these sequences (should tell somebody to dload and send them to me) so i'm interested to hear about your attempts to decode these. perhaps a mere yuy2 decoder of huff could do. or ms' (from directx). |
Its raw YUV data. use avisynth with rawsource:
| CODE |
loadplugin("d:\avsplugins\rawsource.dll")
rawsource("e:\downloads\720p50_mobcal_ter.yuv", 1280,720, "i420")
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syntax is: rawsource(filename, width, height, colorspace)
@frank:
| QUOTE | | Well, stephanV, both points seem obvious to me |
Good!
| QUOTE | | btw: in your shuttle clip DRFanalyzed it could have been some clue on poor quality because of bpp with the relative warning... |
Well I cant go any higher in bit rate as q1, and q3 is already quite high if you ask me.
And now I'm off to do some b-frame testing. Not with XviD, but x264, since I dont want to install things anymore I won't use anyway.
eeeeeeerrrrrrrrrrr - wait, theres no WAY i can play h264 720p@50fps, so i have to use XviD after all
(or do libav b-frames not crash anymore)
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| i4004 |
| Posted: Aug 29 2005, 09:20 PM |
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ftp://ftp.ldv.e-technik.tu-muenchen.de/pu..._sequences/601/
use that and deinterlace.
i mean, do we care about 720p?
i don't.
btw. saw this
http://forum.doom9.org/showthread.php?p=68...7136#post687136
my experience is simillar; they don't really help. they can bring bitrate down, but with it the quality too.
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| stephanV |
| Posted: Aug 30 2005, 12:18 PM |
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any other wishes? resizing? deinterlacing method?
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