Explanation for new switches in x264

[shon3i]

Can somebody explain new switches in x264

--direct-8x8 <-1|0|1>
--deadzone-inter <int>
--deadzone-intra <int>

and can it improve picture in low-mid bitrate encoding?

[Kostarum Rex Persia]

That's good question. Sharktooth, can you or Bond explain there switches?

Thank you.

[Sirber]

I'm interrested to know too. For RealAnime :D

[IgorC]

--direct-8x8 for better HD-DVD compability.
--deadzone to increase detail level at high bitrates. Noises, filmgrain another misc. details

[Thunderbolt8]

so what would be good examples when to use deadzone (bitrate or which crf number) and what value to enter there then?
btw. i cant see those options to be toggled in megui, hasnt the gui been updated for this yet ?

[Sirber]

Does --direct-8x8 change the quality? or it's just a comptability flag?

[foxyshadis]

Yes, turning it off will probably slightly lower the quality. I have no idea how much or little though. In the past it's always been on (when allowed), but not exposed as an option.

[akupenguin]

In the past it has always been off whenever possible, even when that violated Levels, (under the assumption that off was better quality). Then I ran some tests and found that it had no measurable effect on quality one way or the other, so I fixed it to be compliant.

[foxyshadis]

Oh, I must not have looked back enough in the sources, since it looked like it could be set on in the old diffs. Sorry!

[AlexW]

Hi everybody.

As IgorC said --deadzone should help to preserve more fine details and film grain at medium - high bitrates, i would suggest that people start by tweaking --deadzone-intra because that seems to make the most difference here, the default value for --deadzone-intra is 11 but something closer to 0 should help detail preservation a bit, it might also be beneficial to combine it with a CQM.

[Sharktooth]

Uhm... doing some usual movie trailers encodings...

[virus]

Hi everybody.
OMG he has talked :D :p ;)

(9 patches committed to x264's SVN, 6 posts. this guy must have a zipper instead of a mouth :p)

[lexor]

Hi everybody.

[...] --deadzone should help to preserve more fine details and film grain at medium - high bitrates [...]
what would you define as medium to high.

for me >3mbps is high, 1.5-3mbps is medium and <1.5mbps is low (this is where most my encodes are). So is the switch unlikely to affect me, or are your numbers lower for respective ranges?

this info should be put in some sticky, I hear people all the time saying low/mid/high bitrate, those words mean nothing without numbers.

[Sharktooth]

when someone generalizes on the bitrate, it means a number would be useless.
It ALL depends on the source compressibility.
Think it this way:
ultralow bitrate = the encoding looks like crap.
low bitrate = the encoding looks acceptable but certainly not good.
mid bitrate = the encoding looks good but it's not perfect.
high bitrate = the encoding looks near perfect.

[Sharktooth]

Hi everybody.

As IgorC said --deadzone should help to preserve more fine details and film grain at medium - high bitrates, i would suggest that people start by tweaking --deadzone-intra because that seems to make the most difference here, the default value for --deadzone-intra is 11 but something closer to 0 should help detail preservation a bit, it might also be beneficial to combine it with a CQM.
Can you please also specify the encoding time relation between default values and user set values>

[lexor]

when someone generalizes on the bitrate, it means a number would be useless.
It ALL depends on the source compressibility.
Think it this way:
ultralow bitrate = the encoding looks like crap.
low bitrate = the encoding looks acceptable but certainly not good.
mid bitrate = the encoding looks good but it's not perfect.
high bitrate = the encoding looks near perfect.
hmm an interesting rating system, quite different from what I do (especially since the thing you rated high is, to my taste, unachievable withing x264+DVD5 limits).

DVD5 = great movie that I'd watch over and over
1/2 DVD5 = a (cult)classic that wouldn't be watched more then a few times a year (if that)
1 CD - 1/3 DVD5 = movie is worth a chuckle, but not the bitrate

this farily stably derives the value ranges I gave above.

Series are of course exempt from the above.

[*.mp4 guy]

Just to give people a bit more of an idea of what deadzone does; Deadzone determines how much "insignificant" information is droped. Higher values of deadzone help avoid artifacts by eliminating useless information at lower bitrates, and freeing up the bitrate that information would have used - to keep more important information with better quality. Lower values preserve more of the original source information, but to reach a given bitrate that information will have to be compressed more then if a higher value of deadzone was used.

Higher values of deadzone will give a cleaner, smoother, less detailed look, while lower values will give a noisier, crisper, higher detail look, similar to older mpeg varients.

Edit: updated the description of deadzones effect, after preliminary testing 6 seems to have about the same detail preservation as Xvid.

[Thunderbolt8]

again my question, i cant find that in megui, so is this implented in the x264 installer only to be found on x264.nl ? if so, will this implemention also be done for the megui (or if its already there enlighten me plz how I can find it).

[asdfsauce]

Use the "Custom CommandLine Options" field in the Zones tab of the x264 configuration window.

[Sharktooth]

again my question, i cant find that in megui, so is this implented in the x264 installer only to be found on x264.nl ? if so, will this implemention also be done for the megui (or if its already there enlighten me plz how I can find it).
it's not implemented in megui (yet).
do what asdfsauce said.

[Thunderbolt8]

ok, thx.

[asdfsauce]

I haven't seen it mentioned in this thread yet, so let me ask. Am I correct in assuming trellis should be turned off for the deadzone switch to have any effect?

[akupenguin]

Yes.
Theoretically, the deadzone switches could apply to trellis too by modifying lambda, but that hasn't been implemented yet.

[AlexW]

Can you please also specify the encoding time relation between default values and user set values>

I haven't tested this much yet, but the effect of custom deadzone on encoding speed should be minimal.

[Prettz]

Excellent. This sounds like just the option I've been needing to deal with a few very tough scenes in Terminator 2 that weren't responding well to just increased bitrate. I'll start testing it ASAP.

[Caroliano]

How deadzone interacts with in-loop deblocking? Is an low value for deblocking needed in order to get good efects from low deadzones values? Or the defaut deblocking (0,0) don't bother?

What's the diference between low deadzone setings and high bitrate CQMs?

Is higher than defaut deadzone values recomended for low-bitrates?

[akupenguin]

Deadzone affects the quality-per-qp. Optimal (absolute) deblocking strength depends on quality. Actual deblocking strength (as defined by the standard and set by x264 options) is relative to qp, not relative to quality. So if you change quality-per-qp, then you might want to modify the deblocking setting.
However, the units of the deblocking setting a pretty coarse. So even if you set deadzone all the way down to 0 (not recommended), the compensating change would be to reduce deblock by at most 1 (compared to whatever deblocking you were previously using with the default deadzone).
Conversely, if you increase deadzone all the way up to 32, I expect the optimal deblock setting to change by at most +1.

There is no particular relationship between bitrate and optimal deadzone. Deadzone is already specified relative to the rate-distorion optimal value, so any changes are psychovisual, and not well enough tested yet to give a definitive recommendation.

[DryFire]

What would be the difference between using your denoiser of choice as opposed to deadzone?

Speed?

[pinkie_1]

A question to the people with a better insight than mine : how are the --deadzone switches correctly used ?
I've noticed that some apparently odd combinations are quite popular. For instance (4,4) or (6,6,), even (0,0)... (mind you, the first parameter stands for intra, the second for inter)
AFAIK :
1. intra should have a lower value than inter
2. (0,0) shouldn't be used at all
Personally, I tend to use (2,4) or (4,8) when tweaking the --deadzone settings is appropriate.