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Old 25th January 2022, 10:26   #1  |  Link
mike23
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Join Date: May 2003
Posts: 107
2-pass AVC H.264 encoding = 5% bitrate improvement over 1-pass?

I am thinking about the quality improvement when using a 2-pass AVC H.264 encoding vs 1-pass AVC H.264

In the past I read many recommendations for 2-pass encoding over only 1-pass.
So I use this 2-pass encoding during the last years.

When I compare now again the results I found hardly any quality differences.

Is this statement still true?

Is there a quality approximation similar to:

2-pass encoding at bitrate X = 1-pass encoding at bitrate (X + 5%)

with same other encoding parameters

?
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Old 25th January 2022, 12:11   #2  |  Link
rwill
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Posts: 159
Quote:
Originally Posted by mike23 View Post
I am thinking about the quality improvement when using a 2-pass AVC H.264 encoding vs 1-pass AVC H.264

In the past I read many recommendations for 2-pass encoding over only 1-pass.
So I use this 2-pass encoding during the last years.

When I compare now again the results I found hardly any quality differences.

Is this statement still true?

Is there a quality approximation similar to:

2-pass encoding at bitrate X = 1-pass encoding at bitrate (X + 5%)

with same other encoding parameters

?
Join Date 2003, not sure if Troll or not.
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Old 25th January 2022, 18:24   #3  |  Link
benwaggoner
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2-pass has more benefit the more variable the content. So security camera footage may get very little, but a long movie of varied scenes can get a lot more.

In essence, a 2-pass encoding is a 1-pass encode that has the benefit of a 1st analysis pass, and thus lookahead over the whole title. With 1-pass, a clip that is very easy to encode in the first half and very challenging in the second half will wind up spending too many bits in the start and have too few left by the end. With 2-pass, the encoder knows how things will change in the future, and is able to vary the bitrate more in order to vary the quality less.
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