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18th January 2008, 02:56 | #1 | Link |
Registered User
Join Date: Nov 2007
Location: Chile
Posts: 22
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CRF OR 2Pass.
Hi, I was wondering...
If a video encoded with CRF 21 has a final target size of, say, 600 mb, then, ¿if I encode the same video with two pass specific bitrate to achieve the same size (600 mb), wich one would have better quality? Does two pass yields better quality at a given size than CRF, or it is the same, meaning two pass is kind of obsolete?? Also, it is safe to say that any divx or xvid source can be encoded to 80% of it´s size with x264 without any quality loss? I´m using Avinapitc to DRF analizye the resulting h264 streams, and I´m confused with some results: I use the megui crf profile to encode a certain video (CRF 21), then I analize the result and it has an average DRF of about 22, but then I modify the megui profile to have it making more exahustive video analisys (--no-fast-pskip, --subme 7, --me umh) and the resulting stream (at the same CRF 21) has less size and has an average DRF of about 24. What does this means? That with more analisys you get a smaller file with worse quality or a smaller file with the same quality but with a lower DRF average? And why does the megui profile CRF uses just the least pixel refinement posible setting (1) ? |
18th January 2008, 03:00 | #2 | Link | ||||
x264 developer
Join Date: Sep 2005
Posts: 8,666
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Quantizers can vary due to the encoding settings because depending on the source, enabling RDO/similar will either raise or lower the bit cost of encoding, resulting in different quantizer choices to be made. |
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18th January 2008, 04:06 | #3 | Link |
Registered User
Join Date: Nov 2007
Location: Chile
Posts: 22
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Thanks Dark!
I was reaching the same conclution: CRF and twopass are about the same in quality. The DRF analisys of both the two pass and the crf encoding shows almost the same average drf. However in the two pass encode the quantitizers are very normally distributed, and on the crf the quantitizers tend to concetrate on one extreme. ¿Could this normal distribution mean a wiser bit usage than on crf? |
18th January 2008, 04:06 | #4 | Link | |
x264 developer
Join Date: Sep 2005
Posts: 8,666
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18th January 2008, 04:12 | #5 | Link |
Mr. Sandman
Join Date: Sep 2003
Location: Haddonfield, IL
Posts: 11,768
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the profile uses subme 1 coz ppl asked for faster 1pass CRF profile. you're free to modify it.
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MPEG-4 ASP Custom Matrices: EQM V1(old), EQM AutoGK Sharpmatrix (aka EQM V2), EQM V3HR (updated 01/10/2004), EQM V3LR, EQM V3ULR (updated 04/02/2005), EQM V3UHR (updated 17/12/2004) and EQM V3EHR (updated 05/10/2004) Info about my ASP matrices. MPEG-4 AVC Custom Matrices: EQM AVC-HR Info about my AVC matrices My x264 builds. Mooo!!! |
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