Quote:
Originally Posted by almosely
Hi there,
a few minutes ago I updated Simple x264 Launcher and started a .avs-x264-encoding. Something is working wrong. The first issue is: I chose CRF 18.4 but in the joblist is stated "CRF@18". The job details is displaying the correct value, "--crf 18.4". The second issue is: I got insane quantizers listed in the logfile (I-frames Avg-QP=26.55, P-frames Avg-QP=30.35, B-frames Avg-QP=31.93). Both worked fine with the non-updated version before (I don't remember, which version that was, maybe something from april 2016). When I analyze the encoded file with AVInaptic, I get different, more realistic quantizers (I-slices avg DRF=13.91, P-sclices avg DRF=17.61, B-slices avg DRF=19.06). I know that AVInaptic normally differs from the Simple x264 Launchers logfile, but it has never been that much.
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The CRF value displayed in the job name is a
rounded value - for the sake of simplicity. So this is
not necessarily the
exact CRF value that you specified and that will be passed to x264.
I'm pretty sure that, if you look at the actual x264 command-line (in your log), you will realize that the "correct" CRF value has been passed to x264.
Also note: In CRF mode, the QP values are allowed to fluctuate as needed. The x264 developers decided to make the CRF value live on the same scale as the QP values, but that was a completely arbitrary decision! Internally, x264 will multiply the value that you passed via
--crf parameter with some "magic" number in order to compute the
actual constant "rate factor" which will be used for encoding. That "magic" number has been tuned so that using
--crf x roughly results in an
average QP of
x. Again, this was an arbitrary decision. And the tuning was done with a specific set of source clips. Consequentiality, you can
not expect that
--crf x will result in an average QP of exactly
x. It may depend a lot on your particular source video!
In a quick test with "--crf 18.4" and "medium" preset, I got this result:
Quote:
x264 [info]: frame I:401 Avg QP:14.87 size: 35850
x264 [info]: frame P:7835 Avg QP:17.73 size: 13307
x264 [info]: frame B:19384 Avg QP:19.72 size: 5328
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