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Old 12th December 2017, 10:42   #21  |  Link
excellentswordfight
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Quote:
Originally Posted by jd17 View Post
I did not know that is possible.
However, what would be the benefit?

Isn't one of the reasons to use a CRF instead of a bitrate target to be freed from any bitrate constraints?

I thought CRF uses whatever bitrate necessary for each moment to achieve a certain degree of quality...
If CRF uses whatever is needed - what difference would a 2pass encode even make?
CRF with maxrate and bufsize constrains would imo only make sense for big streaming services, the use of CRF there would not be to increase quality but to lower filesize (i.e. storage cost) without much of an quality loss for low complexity material.

So for 1080p24 streaming it would look something like this
Code:
--crf 20 --vbv-maxrate 9000 --vbv-bufsize 12000 --keyint 48 --min-keyint 24 --rc-lookahead 48
And agree, I dont see a good reason for 2pass CRF even if it's possible.

Nico8583, what are kind of playback environment are you aiming for? It sounds like CRF encoding with the lowest preset you find tolerable is what you are looking for. I would start at preset slow crf 18 and go from there.

Last edited by excellentswordfight; 12th December 2017 at 10:59.
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Old 12th December 2017, 19:10   #22  |  Link
Nico8583
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Thank to all
excellentswordfight, I want to play some Blu ray to x265 movies stored to my NAS on a Samsung 55" TV with a HTPC or a Zidoo X9S. I think to go to CRF18 and Slow preset.
Is the number of threads has an impact to quality ? I can encode on a 4 cores but perhaps I can access to a 16 cores (2 x Intel Xeon 8 cores).
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Old 12th December 2017, 21:02   #23  |  Link
jd17
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Maybe this helps, I created some statistics for my encodes...


Average bitrate of 28 CRF19 / slow / no-sao / 10bit Blu-ray encodes ("regular" movies for me):
5613 kbit/s
That average does include two movies with extreme grain, 14300 and 19000 kbit/s.
Excluding them in the average brings it down to:
4766 kbit/s

Lowest bitrate encode is 2572 kbit/s.


Average bitrate of 27 CRF17 / slow / no-sao / 10bit Blu-ray encodes ("reference" movies for me = very good image quality):
6902 kbit/s
One high grain movie is included (12194 kbit/s).
Average without it:
6699 kbit/s

Lowest bitrate encode is 3777 kbit/s.


These numbers might not seem very low, but you have to consider that these are extremely high quality, transparent or near transparent encodes.
Calculating a similar average for transparent x264 encodes would result in something like 12000-16000 kbit/s.
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Old 12th December 2017, 21:11   #24  |  Link
Nico8583
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Thank you for these informations
Could you give an example of command line ? And why no-sao gives a better quality ? All fast presets use no-sao but all slow preset use sao.
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Old 12th December 2017, 21:16   #25  |  Link
sneaker_ger
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Quote:
Originally Posted by Nico8583 View Post
Is the number of threads has an impact to quality ?
More threads can hurt quality but it should be negligible for most users. I would leave threads/pools at auto.
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Old 12th December 2017, 21:23   #26  |  Link
Nico8583
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Quote:
Originally Posted by sneaker_ger View Post
More threads can hurt quality but it should be negligible for most users. I would leave threads/pools at auto.
I let it to auto and x265 detects 4, 8 or 16 threads.
I read more threads can hurt quality with x264 but I didn't know with x265, so it's the same, thank you. Do you know a document about that ( threads number vs quality) ?
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Old Yesterday, 10:09   #27  |  Link
jd17
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Quote:
Originally Posted by Nico8583 View Post
Could you give an example of command line ?
I use Handbrake, Hybrid or both for my encodes. I see no drawbacks in doing that. It makes things comfortable and saves me some time.

That being said, there are no changes to the x265 defaults in my encodes apart from:
--output-depth 10
--preset slow
--no-sao
--crf 17 / 19
--keyint 240 (for 23.976p / 24p movies)
--min-keyint 24 (for 23.976p / 24p movies)

Quote:
And why no-sao gives a better quality ?
I suggest you make a few comparisons yourself.

Here are links to some old stills I created:
https://forum.doom9.org/showpost.php...9&postcount=17

They were done with preset medium, but that does not matter since you can just compare sample 4 and 5 to see the impact of sao and look at sample 1 for reference.
The difference between --sao and --no-sao would be similar with slow encodes.

The gist for me:
--sao = blurred, smoothed
--no-sao = detailed, grain retention, much closer to the source

(People around here sometimes translate SAO to "smooth all objects" for fun. You might understand why... )

Quote:
All fast presets use no-sao but all slow preset use sao.
Only ultrafast and superfast disable --sao by default. I think the reason for that is, that encoding without --sao is also a bit quicker. It's not much but every little bit counts for these "extreme" presets.
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Old Yesterday, 10:35   #28  |  Link
Nico8583
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Thank you, I'll look at it when I'll be at home.
Do you have made new tests with newer version of x265 ? It seems there are some improvments with sao, no ?
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Old Yesterday, 10:55   #29  |  Link
jd17
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To my knowledge, nothing changed since 2.4 regarding sao.

https://x265.readthedocs.io/en/defau...easenotes.html
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Old Yesterday, 22:20   #30  |  Link
Nico8583
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You're right
I'm going to make some tests like you with a short Blu ray movie (8bit vs 10bit, medium vs slow, sao vs no-sao, CRF18 vs CRF20...)
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