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Old 10th February 2009, 21:06   #1  |  Link
b66pak
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Encoding with h264 at low bitrates [bits/(pixel*frame): 0.09 - 0.11]

Hi. I want to encode some tv shows with h264 (using megui) at low bitrates [bits/(pixel*frame): 0.09 - 0.11].

For those unfamiliar with this it means for example: 1/4 cd-r (175mb) for 42min (average) at 624x352@24fps or 1/8 cd-r (87.5mb) for 21min (average) at 624x352@24fps.

Can you suggest downsizing methods, custom matrix, megui profiles, your experience etc?

Thanks a lot.
_

Last edited by b66pak; 10th February 2009 at 21:23.
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Old 10th February 2009, 21:09   #2  |  Link
Dark Shikari
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0.1 is now considered low?

On that note, BPP is a terrible measure of quality.

Last edited by Dark Shikari; 10th February 2009 at 21:11.
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Old 10th February 2009, 22:28   #3  |  Link
Atak_Snajpera
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BTW . Who created this ridiculous value???
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Old 10th February 2009, 22:50   #4  |  Link
Esurnir
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BTW . Who created this ridiculous value???
AutoGK?
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Old 10th February 2009, 23:06   #5  |  Link
D734
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so around ~550kbps bitrate (AACplus2 suggested over mp3 to).
i've done some of those a while ago with SGA (for fun and learning experience)
i don't use megui anymore but when i did sharktooth profiles worked good with settings.
dxva-hd-insane (even tho your doing sd encodes) would be a good idea as it doesn't do 16 ref frames (like unrestricted insane) which can double encoding time (also as i hear 5-6 is the most you normally need unless anime/cartoon).
some people dont like to do me=tesa (satd exaustive) because it slows things down a bit but you may want that over umh (multi hex) considering the low bitrate your doing.

also note that for the encodes, re-encoding a 720p x264 to 624x352 x264 will give better results then just re-encoding a 624x352 xvid to 624x352 x264
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Old 10th February 2009, 23:26   #6  |  Link
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also note that for the encodes, re-encoding a 720p x264 to 624x352 x264 will give better results then just re-encoding a 624x352 xvid to 624x352 x264
Oh my god! you've just discovered america
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Old 10th February 2009, 23:58   #7  |  Link
D734
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also note that for the encodes, re-encoding a 720p x264 to 624x352 x264 will give better results then just re-encoding a 624x352 xvid to 624x352 x264
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Oh my god! you've just discovered america
lol, its a no brainer but you would actually be surprised how many dont know that.
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Old 11th February 2009, 00:46   #8  |  Link
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AutoGK?
first seen in the original Gordian Knot i belive?
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Old 11th February 2009, 01:33   #9  |  Link
Sagekilla
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Ignoring the fact that bpp is meaningless, ~500 kbps (bpp = 0.1 for 624x352 @ 24 fps) would give you very good quality. Hell, my own DVD rips @ 848x480 average around 1 mbps for the video. Extrapolating backwards, that would make a bitrate of around ~500 kbps also good for your video. (Note: Bitrate scaling isn't linear to resolution. Doubling the resolution usually requires less than twice the bitrate, and halving the resolution might not always require half the bitrate).

Stop using pointless metrics like bpp and just stick with crf mode. crf = 20 - 22 should give you very good quality at low bitrates.
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Old 11th February 2009, 07:49   #10  |  Link
ajp_anton
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Note: Bitrate scaling isn't linear to resolution. Doubling the resolution usually requires less than twice the bitrate, and halving the resolution might not always require half the bitrate
If double res needs less than double bitrate, then half res needs more than half bitrate (at least when "half res" = original res, halved from the doubled one).
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Old 11th February 2009, 12:14   #11  |  Link
DJ Bobo
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I don't know what's wrong with taking bpp as an approximating quality measure. I'm aware that different videos may require different bpp, but it's a fast "rule of thumb" for those who don't have time to do compressiblity tests and stuff, and need to hit a specific size target.

I would agree that going below 0.1bpp is not healthy and that it's considered a low bitrate. Did you ever see a blu-ray disc with less than 5GB for the main movie?? I didn't think so.
Even 720p rips hit the 4GB mark easily, which results in about 0.25bpp.
But, b66pak, I would still go with light bicubic resizing (default avisynth setting) instead of bilinear, bilinear washes too much for my taste. Make sure to filter the noise well though.

@Sagekilla: what's up with you guys following that "upsizing trend"?! encode anamorphic, let the player handle the upsizing! MPC HC can do bicubic resizing, I don't know what's wrong with that! just wasting bitrate for nothing IMHO...
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Old 11th February 2009, 13:48   #12  |  Link
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I use crf 22 for my rips and bpp vary greatly. I looked at some movies on my harddrive now (blu-ray rips, 720p or equivalent number of pixels) and the bpp values are between 0.1 and 0.35. Assuming that crf gives a more or less constant quality difference between source and encode that makes bpp pretty useless, because while you can say most movies above ~0.3 bpp will look good it doesn't tell you anything about the quality of rips below that value and there are still cases where this is not enough. Also with higher resolutions you can generally get away with less bitrate so you'd have to take that also into account.
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Old 11th February 2009, 14:21   #13  |  Link
Sharktooth
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how many times i have to say BPP is a completely useless metric?
leave it alone. use CRF instead or do a compression test if you need to hit a filesize.
BPP is useless. period.
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Old 11th February 2009, 16:58   #14  |  Link
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As said, I'm well aware of the limitations of the bpp index, but in times of "time is money", you can get away with it as an approximation for the quality you should be expecting.

Anything below 0.1bpp should look like crap
Anything between 0.1 and 0.2bpp should look good
Anything above 0.2bpp should look very good
- providing right filtering! -
And as they say, exceptions confirm the rule

No doubt that a compressibility test is the best method, I'm not arguing about that, don't worry, we're on the same side

OLD SCHOOL ISN'T THAT BAD GUYS!
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Old 11th February 2009, 17:09   #15  |  Link
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how many times i have to say BPP is a completely useless metric?
leave it alone. use CRF instead or do a compression test if you need to hit a filesize.
BPP is useless. period.
Given that bpp is crap how useful is a compression test? I run it just about every time I encode something but for some reason I'm never happy with the 50%. I always bump it up to 60 to 80%.

Got a link to where I can study what it actually does?
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Old 11th February 2009, 17:21   #16  |  Link
DJ Bobo
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@ DW
I'll try to explain the compressibility test with DivX terms: 100% uses the lowest possible quantizer, which is 2 in the case of DivX. 50% equates Quantizer 4. 75% Quantizer 3. You seem to dislike anything higher than Quantizer 3.
Quantizers are a bit different in the h.264 world, but they follow the same logic.
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Old 11th February 2009, 18:11   #17  |  Link
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As said, I'm well aware of the limitations of the bpp index, but in times of "time is money", you can get away with it as an approximation for the quality you should be expecting.

No doubt that a compressibility test is the best method, I'm not arguing about that, don't worry, we're on the same side
Or you can be smart and not waste -any- time by just using crf. crf 20 will give about the same quality every time you use it. Only one run needed. No need to do a compressibility pass, or relying on on bpp to tell you what size you need.

It's not a bash against "old school methods." It's just being smart. Like everyone said, and as you acknowledged, a bpp of X will look great on one video but horrid on another. But, crf of Y on one video will look just as good on one video as it does on every other.

Save your time, stop doing guess work, and use crf.

Edit: Yes I know I can just encode anamorphic video. No longer a concern of 720x480 or 848x480 though. 720p rips of Blu-ray all the way
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Old 11th February 2009, 19:17   #18  |  Link
DJ Bobo
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@ Sagekilla
Am I missing something here? I thought CRF-encoding is for people that don't care about final file size?!
The point behind bpp is to get a quick approximation of what the resolution should be for a given target file size (I don't know if you got this specific point right)
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Old 11th February 2009, 19:37   #19  |  Link
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Back to the original topic/theme regarding tips for lower bitrate encoding:

-Depending on the source / desired goal, preprocessing with some denoising filters might help lower bitrate requirements

-Use higher quality x264 encoder settings

-I would disable psy rd /psy trellis, they tend to "eat up" too much bitrate , and ringing artifacts are more readily visible at low bitrates

It will take you a few minutes to test out various settings on a short representative clips
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Old 11th February 2009, 22:31   #20  |  Link
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Hi. I was given the BPP value so we can quickly get the bitrate for a desired resolution@framerate and NOT as a quality measure...

Example:

-for 1920x1080@24fps BPP 0.1 we talking about 4977kb/s

-for 1280x720@24fps BPP 0.1 ... 2212kb/s

-for 720x480@24fps BPP 0.1 ... 830kb/s

-for 720x576@25fps BPP 0.1 ... 1037kb/s

-for 640x368@30fps BPP 0.1 ... 706kb/s

-for 640x368@24fps BPP 0.1 ... 566kb/s

-for 624x352@30fps BPP 0.1 ... 660kb/s

-for 624x352@24fps BPP 0.1 ... 527kb/s

you get the ideea...

thank you Sagekilla! i didn't know that bitrate scaling isn't linear to resolution...

Dark Shikari provided (on the first reply) a 10min cartoon (1920X1080@24fps) at a stunning BPP 0.03!!!


now lets talk about avisynth resizing for low bitrates...

DJ Bobo kindly suggested soft bicubic resize...what about neutral or sharp resizing?...pro and contra...
_

Last edited by b66pak; 12th February 2009 at 03:12.
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