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Old 9th November 2013, 19:26   #1  |  Link
montreal.simo
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Subme & aq-mode

Hi all,

I'm using x264 to encode two videos (one video with low motion- head talking, and a second is a part from movie). The command line is: x264 --preset ultrafast --tune zerolatency --subme xx --aq-mode yy .
I have too questions about Subme and Aq-mode parameters:

Subme:

Encoding the video for different subme value gives:

subme Bitrate PSNR
0 5417.87 38.796
1 3807.03 39.578
2 2727.20 38.681
3 2647.04 38.750
4 2639.97 38.754
5 2648.79 38.772
6 2786.14 38.836
7 2786.14 38.836

I'm wondering why subme 2 gives the worst quality? And subme 1 improves quality!!


aq-mode :

Encoding the head talking video (low motion) shows that using aq-mode 1 or 2 reduces bitrate and quality than aq-mode 0. But encoding the part of movie (high motion) shows that aq-mode increase bitrate and improves quality than aq-mode 0. Can someone explain it to me??

Thanks for help.
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Old 9th November 2013, 19:35   #2  |  Link
sneaker_ger
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You're comparing different settings at different bitrates so your results are meaningless for the most part. CRF encoding does not guarantee constant quality over different settings.
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Old 9th November 2013, 19:36   #3  |  Link
Groucho2004
 
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Quote:
Originally Posted by montreal.simo View Post
Subme:

Encoding the video for different subme value gives:

subme Bitrate PSNR
0 5417.87 38.796
1 3807.03 39.578
2 2727.20 38.681
3 2647.04 38.750
4 2639.97 38.754
5 2648.79 38.772
6 2786.14 38.836
7 2786.14 38.836

I'm wondering why subme 2 gives the worst quality? And subme 1 improves quality!!
It has been discussed here many, many times: It's pointless to compare the quality if the bitrate is not the same.
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Old 9th November 2013, 20:00   #4  |  Link
montreal.simo
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I agree with you.
But, Im looking to the variation of both bitrate and quality for every subme value. My goal is to choose the right subme.
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Old 9th November 2013, 20:07   #5  |  Link
Groucho2004
 
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Quote:
Originally Posted by montreal.simo View Post
I agree with you.
But, Im looking to the variation of both bitrate and quality for every subme value. My goal is to choose the right subme.
There is no "right" subme value. The higher you set it, the better the quality will be (more or less) at a given bitrate.
If you want to compare the subme settings you have to adjust other settings (like CRF) to make sure the bitrate is the same. Or use 2 pass encoding.
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Old 9th November 2013, 22:05   #6  |  Link
montreal.simo
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Quote:
Originally Posted by Groucho2004 View Post
There is no "right" subme value. The higher you set it, the better the quality will be (more or less) at a given bitrate.
If you want to compare the subme settings you have to adjust other settings (like CRF) to make sure the bitrate is the same. Or use 2 pass encoding.
I did adjust the CRF to fix the bitrate, the result is as below :
crf subme bitrate PSNR
25 0 5417.87 38.796
23 1 5445.89 40.759
21 2 5570.54 40.919
21 3 5468.91 40.955
21 4 5461.33 40.958
21 5 5463.10 40.972

the PSNR look fixed too ??
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Old 9th November 2013, 22:17   #7  |  Link
Groucho2004
 
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Quote:
Originally Posted by montreal.simo View Post
I did adjust the CRF to fix the bitrate, the result is as below :
crf subme bitrate PSNR
25 0 5417.87 38.796
23 1 5445.89 40.759
21 2 5570.54 40.919
21 3 5468.91 40.955
21 4 5461.33 40.958
21 5 5463.10 40.972

the PSNR look fixed too ??
Not sure what you mean by "fixed" but the trend in the table shows what was to be expected. I doubt that the numbers are going to help find your "right" value. The best way to judge quality is still just looking at the result.
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