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6th July 2020, 13:20 | #1 | Link |
Herr
Join Date: Apr 2009
Location: North Europe
Posts: 556
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x265: --rc-lookahead values?
I wonder, should I set the value of
--rc-lookahead to the amount of frames per second the encode-video got? Like 24 (or 2*24 3*24 and so on), if the source got 24FPS. Or does that not matter? Thanks. Last edited by Forteen88; 6th July 2020 at 14:06. Reason: clarifying |
6th July 2020, 16:21 | #3 | Link |
Lost my old account :(
Join Date: Jul 2017
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For very open I-frame placement cases were you have a large max keyint of say 10s of video, I have a hard time to believe that there will be any difference for most people if say 24 or 25 is used for 24p video. It will be pretty much the same case as if you wanna keep the default keyint at 25/250 or change it to "match" the fps, there will be some edge cases were it will do difference but most of the time it's probably an vanity setting.
However, I rarely use x265 for personal encoding, and is almost always using it with fixed GOP-sizes/chunks, and for that I always set the rc-lookahead to contain the whole GOP, which is always in multiples of the fps. And personally when I do use it... Yeah I have some issues, I cannot stand min and max keyint, and lookahead to not be multiples of the fps. And since it doesn't really effect speed that much (more RAM usage and letancy) I usually go up to 2-4s, cause it does in fact change the slice decision in encodes when the value increases from the "normal" levels of around 20 to arround 40-60, and I guess thats its increased in the higher presets cause its beneficial. Not sure what you wanna say with that post, it doesnt answer OP question and 60 is not the max value for the setting in question. Some context would've been nice. Last edited by excellentswordfight; 6th July 2020 at 16:43. |
7th July 2020, 01:25 | #4 | Link |
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Max is --keyint. I think anything more than keyint minus min-keyint isn't going to do much. Using high values increase memory utilization a lot but don't seem to impact speed so much.
Last edited by benwaggoner; 7th July 2020 at 16:31. Reason: Clarified text |
7th July 2020, 10:09 | #5 | Link | |
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7th July 2020, 11:41 | #6 | Link |
Herr
Join Date: Apr 2009
Location: North Europe
Posts: 556
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Except it really doesn't decrease speed of the encoding much at all, just a tiny bit. I did a test-encode and --rc-lookahead 85 only added like 15 seconds compared to a --rc-lookahead 48 encode that took 12:23 minutes.
Last edited by Forteen88; 7th July 2020 at 11:45. |
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