x264 rc-lookahead

[jedson]

Many thanks for this site.

I'm using the latest Hybrid version (rev 2022.03.20.1) for Mac.

I'm making an x264 encode of an NTSC video source using the "slower" preset and QTGMC deinterlace filter.  I've adjusted some of the values to comply with the requirements of the site where I upload.  What is happening is that even though rc-lookahead is set for 60, the output file shows rc-lookahead=0 when I check it with MediaInfo.  I'm not sure what is going on.  Any help is appreciated.

Thanks again!

[Selur]

Note that: rc-lookahead is a encoding side parameter, so it has no influence in regard to compatibility
That said, I'll try to look into it after work and report back.
--
I checked the used encoding calls:
1st pass encoding call:

"/usr/local/bin/vspipe" "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/encodingTempSynthSkript_2023-02-07@13_54_15_8510.vpy" - -c y4m | "/Applications/Hybrid.app/Contents/MacOS/x264" --pass 1 --bitrate 2000 --profile high --level 4.1 --ref 1 --keyint 250 --min-keyint 0 --scenecut 40 --bframes 16 --b-bias 0 --b-pyramid normal --direct auto --b-adapt 2 --sync-lookahead 12 --cplxblur 20.0 --qcomp 0.60 --qblur 0.50 --no-mbtree --rc-lookahead 60 --ipratio 1.40 --pbratio 1.30 --chroma-qp-offset 0 --qpmin 0 --qpmax 69 --qpstep 4 --partitions none --no-8x8dct --8x8dct --me dia --mvrange -1 --subme 2 --cabac --trellis 0 --weightp 2 --aq-mode 1 --aq-strength 1.00 --nr 0 --deadzone-inter 21 --deadzone-intra 11 --cqm flat --threads auto --sar 8:9 --qpfile "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/Test_2023-02-07@13_54_15_8510_08.qp" --deblock -2:-2 --non-deterministic --range tv --stats "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/Test_2023-02-07@13_54_15_8510_09.stats" --demuxer y4m --input-range tv --fps 60000/1001 --output-csp i420 --output-depth 8 --output /dev/null -

2nd pass encoding call:

"/usr/local/bin/vspipe" "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/encodingTempSynthSkript_2023-02-07@13_54_15_8510.vpy" - -c y4m | "/Applications/Hybrid.app/Contents/MacOS/x264" --pass 2 --bitrate 2000 --profile high --level 4.1 --ref 8 --keyint 250 --min-keyint 0 --scenecut 40 --bframes 16 --b-bias 0 --b-pyramid normal --direct auto --b-adapt 2 --sync-lookahead 12 --cplxblur 20.0 --qcomp 0.60 --qblur 0.50 --no-mbtree --rc-lookahead 60 --ipratio 1.40 --pbratio 1.30 --chroma-qp-offset 0 --qpmin 0 --qpmax 69 --qpstep 4 --partitions all --8x8dct --me umh --merange 16 --mvrange -1 --subme 10 --cabac --trellis 2 --psy-rd 1.00:0.00 --weightp 2 --aq-mode 1 --aq-strength 1.00 --vbv-maxrate 62500 --vbv-bufsize 78125 --nr 0 --deadzone-inter 21 --deadzone-intra 11 --cqm flat --threads auto --sar 8:9 --qpfile "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/Test_2023-02-07@13_54_15_8510_08.qp" --deblock -2:-2 --non-deterministic --range tv --colormatrix bt709 --stats "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/Test_2023-02-07@13_54_15_8510_09.stats" --demuxer y4m --input-range tv --fps 60000/1001 --output-csp i420 --output-depth 8 --output "/private/var/folders/yy/31psqpj105z4fb4kkt989rr80000gn/T/2023-02-07@13_54_15_8510_10.264" -

Those look fine to me. I don't see any issue in the calls.

=> got it, you disabled mb-tree, without mb-tree rc-lookahead isn't used in the encoding and thus x264 reports it as 0.
So if you want it, you need to enable: 'x264->Rate Control->Rate Control Settings->Macroblock tree rate control'.

Cu Selur

[jedson]

I see.  Thank you.

So there is no way to disable mbtree AND use rc-lookahead at the same time?  Is that true of all encoders?  Or just when using Hybrid?

Thanks again.

[Selur]

That's true for x264, so anything that uses x264 will only use rc-lookahead if mbtree is used.
iirc some older x264 version did write the configured rc-lookahead setting into the sei-block (<-this is what MediaInfo shows), even when it was not used. But for quite some time x264 wrote 0 in the sei-info when rc-lookahead wasn't used.

Cu Selur

[jedson]

Many thanks!