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Old 27th December 2014, 11:40   #1  |  Link
RRD
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Does --ratetol have any effect on a x264 --crf encode without VBV?

Hello. I just realized I forgot to remove --ratetol 8.0 in my x264 encoding command line after doing some tests with --bitrate encodes, which means I've encoded my recent videos with both --crf and --ratetol in the command line. Does it have any negative impact? The wiki (excerpt below) doesn't mention anything so I assume it has no effect, but you never know. Also I'm NOT using any --vbv setting. Thanks.

http://mewiki.project357.com/wiki/X264_Settings#ratetol
Quote:
ratetol
Default: 1.0


This is a dual purpose parameter:
  • In 1-pass bitrate encodes, this settings controls the percentage that x264 can miss the target average bitrate by. You can set this to 'inf' to disable this overflow detection completely. The lowest you can set this is to 0.01. The higher you set this to the better x264 can react to complex scenes near the end of the movie. The unit of measure for this purpose is percent (eg, 1.0 = 1% bitrate deviation allowed).

    Many movies (any action movie, for instance) are most complex at the climatic finale. As a 1pass encode doesn't know this, the number of bits required for the end is usually underestimated. A ratetol of inf can mitigate this by allowing the encode to function more like a --crf encode, but the filesize will blow out.

  • When VBV is activated (ie, you're specified --vbv-* options), this setting also affects VBV aggressiveness. Setting this higher allows VBV to fluctuate more at the risk of possibly violating the VBV settings. For this purpose, the unit of measure is arbitrary.
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Old 27th December 2014, 12:27   #2  |  Link
MasterNobody
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No. It doesn't have any effect (not used) in case of CRF without VBV except writing different ratetol value to SEI with settings. With VBV it would have some effect.
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