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3rd June 2011, 09:45 | #1 | Link |
Registered User
Join Date: Aug 2010
Posts: 12
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2 B frames encoding time anomaly
Could someone explain to me the anomaly why x264 encoder needs more time for encoding with 2 B frames than with 3 B frames?
I made test where I encoded a video sequence with various number [0..16] of B frames between keyframes. The best quality was achieved with 2 and 3 B frames but for some reason 2 B frames require more encoding time than 1 or 3 B frames. Test can be found here. |
5th June 2011, 01:23 | #3 | Link |
x264 developer
Join Date: Sep 2004
Posts: 2,392
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Pyramid is slower than non-pyramid, because pyramid allows the use of more references, namely the 2nd future ref in disposable b-frames prior to the B-ref. Pyramid is enabled by default when B>=2. Pyramid with B==2 has a greater fraction of "disposable b-frames prior to the B-ref" than B==3 does. And indeed, the speed bump goes away if you set ref=1 and/or pyramid=none.
Pyramid=strict is faster than pyramid=normal because strict forbids the use of some refs that normal allows. This is not an optimization, just a loss of an opportunity. |
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