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x264 encoding times in CRF and VBR second-pass differ by twice

MPEG-4 AVC / H.264 - Doom9's Forum - forum.doom9.org
Dear experts

i observe a strange issue with x264 (version 0.142, compiled by gcc).

On same content and with almost same parameters encoding time (user time) of single-pass CRF is about twice smaller than that of second-pass VBR.

For example gprof reveals that the function 'x264_macroblock_deblock_strength' in VBR run takes ~19s while in CRF run it takes ~3s.

The function actually does not depend on content but it accesses 'mb.cache' data. Maybe accesses to mb.cache slows down performance in VBR second-pass.

Did anybody experienced similar problem with x264 and can explain the difference in performance between single-pass CRF and second-pass VBR?


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