multithreaded x264 quality loss?

[Boogerlad]

hi, I'm a forum lurker =)
before, x264 used slicing of each frame for multithreading, but I heard it's now a frame based multithreading system. Is there still that quality loss for each additional thread? If so, how much percentage?

thanks!

[Dark Shikari]

Negligible.

[Boogerlad]

one more question; Is it possible to go even better than the quality in the "placebo" preset?

[Mutant_Fruit]

Sure, use lossless ;)

[Boogerlad]

doesn't lossless give you the worst compression ratio? like, ultra fast and placebo could be the same size, but placebo would look better. Lossless would look better than placebo, but the file size would be bigger.

[Audionut]

--preset placebo --tune grain --keyint 24 --qpmin 0 --chroma-qp-offset -12 --merange 256

[Dark Shikari]

--preset placebo --tune grain --keyint 24 --qpmin 0 --chroma-qp-offset -12 --merange 256At the same bitrate, that will probably produce much worse results ;)

[onesloth]

one more question; Is it possible to go even better than the quality in the "placebo" preset?

There is a reason the preset is named 'placebo':rolleyes:

[sonnati]

Recently I tested a server with two 6-cores (12 threads) xeons for a total of 24 threads. Using a preset veryslow and thread auto I have had a lot of artifacts in fast moving scenes expecially in CBR where the final average bitrate was considerably lower than the desired.
This strange behaviour disappeared setting a low thread number, like 6 or 8.

[Dark Shikari]

Recently I tested a server with two 6-cores (12 threads) xeons for a total of 24 threads. Using a preset veryslow and thread auto I have had a lot of artifacts in fast moving scenes expecially in CBR where the final average bitrate was considerably lower than the desired.
This strange behaviour disappeared setting a low thread number, like 6 or 8.Ratecontrol tends to not adapt fast enough for 1-pass CBR at extremely large thread numbers. I would recommend avoiding very large thread numbers for that reason in CBR mode.

[burfadel]

Generally CBR should be avoided if possible anyway, if encoding to a certain bitrate to ensure a final output filesize 2-pass (ABR) is much more suitable. If file size isn't so much an issue and you want to approximate an output quality then CRF may be more suitable.

If you want something decent above standard settings, try something like:
<code>--rc-lookahead 80 --nr 900 --bframes 6 --b-adapt 2 --direct auto --subme 10 --trellis 2 --psy-rd 1:0.4 --me umh --merange 24 --aq-mode 2 --sync-lookahead 24</code>

Very similar to the presets, but they're my preferred settings...

Main things for me are --subme 10, --trellis 2, --me umh, and --aq-mode 2

[sonnati]

Thank you DS.

PS: I need CBR because I'm encoding for Satellite Broadcasting.