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Old 20th August 2012, 07:39   #1  |  Link
bxyhxyh
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Different Settings in 1st and 2nd pass

If i use

Encode 1
1st pass --preset placebo --bitrate 800
2nd pass --preset fast --bitrate 800
Encode 2
Automated 2 pass --preset fast --bitrate 800

Which encode is better quality? Or they're same?

Last edited by bxyhxyh; 20th August 2012 at 07:50.
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Old 20th August 2012, 17:32   #2  |  Link
LoRd_MuldeR
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Quote:
Originally Posted by bxyhxyh View Post
Encode 1
1st pass --preset placebo --bitrate 800
2nd pass --preset fast --bitrate 800
Despite the fact that "placebo" never gives any noteworthy improvement over "veryslow" (it only is a LOT slower), using slower settings in the first pass of a 2-Pass encode doesn't make much sense. If at all, you would be using faster settings in the first pass and slower settings in the second one! And actually that is what x264 does automatically for you: x264 will overwrite your settings with "fast" settings, when you set "--pass 1" but do not set "--slow-firstpass" too. And it's good that way.

So after all, what you'd want is something like:
Code:
x264.exe --pass 1 --preset veryslow
x264.exe --pass 2 --preset veryslow
Note: We use the identical preset for both passes and let x264 speed-up our settings in the first pass automatically.
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Old 20th August 2012, 17:41   #3  |  Link
bxyhxyh
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Sorry my english is not so good. Some questions may not clear.

Code:
x264.exe --pass 1 --preset veryslow --bitrate 800
x264.exe --pass 2 --preset veryfast --bitrate 800
Code:
x264.exe --pass 1 --preset veryfast --bitrate 800
x264.exe --pass 2 --preset veryfast --bitrate 800
Now which is better quality.

Normally i just use veryslow for both passes. Just for knowledge If i use better/worse settings in first pass, it affects quality? Or doesn't?

Last edited by bxyhxyh; 20th August 2012 at 17:44.
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Old 20th August 2012, 18:20   #4  |  Link
MasterNobody
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Code:
x264.exe --pass 1 --preset veryslow --bitrate 800
x264.exe --pass 2 --preset veryfast --bitrate 800
Simply wouldn't work at all (it will error out due different critical options between passes). You need to use same preset for both passes and leave decision how speed up 1st pass to x264.
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Old 20th August 2012, 19:01   #5  |  Link
LoRd_MuldeR
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Moreover it seems he still tries to slow-down the first pass, compared to the second one - which is the exact opposite of what makes sense.
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Old 20th August 2012, 19:19   #6  |  Link
bxyhxyh
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Yes, yes, If i slow down the first pass (without --slow-firstpass), Is quality raise?
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Old 20th August 2012, 19:41   #7  |  Link
Asmodian
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Not if you do not slow down the second pass too.

In fact it will be slightly lower quality as you are using different settings for the first and second passes.

As LoRd_MuldeR said: If you do not set --slow-firstpass, pass 1 forces "--preset fast" settings.
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Old 20th August 2012, 20:12   #8  |  Link
detmek
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Why do you want to slow down first pass and make second pass faster when the main encoding job is done during second pass? The only purpose of first pass is to make rough estimations for second pass. It doesn't make sence to use high quality setting for estimation and use fast, not-so-precise (lower quality) settings for main encoding process. Also:
Quote:
x264.exe --pass 1 --preset veryslow --bitrate 800
x264.exe --pass 2 --preset veryfast --bitrate 800
will not work at all.
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Old 20th August 2012, 20:59   #9  |  Link
LoRd_MuldeR
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The output from the first pass will be discarded anyway, so using slower settings in the first pass is pointless

The one and only thing from the first pass that will survive and is going to be re-used is the "stats" file! All settings that don't effect the "stats" can be lowered safely in order to speed up the first pass!

The final video file that you are going to keep is generated only in the second pass. That's why using slower settings in the second pass (and thus faster settings in the first one) does makes sense.

(And, as explained before, all this happens automatically in x264, so you don't need to take care of it. Simply use the same Preset for both passes!)
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Last edited by LoRd_MuldeR; 20th August 2012 at 21:21.
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