First Pass settings

[ripper64]

Hi,

this is probably discussed before somewhere, but I couldn't find it anywhere, so here my question:

Do I have to set the advanced options like "qpel" and "trellis" the same in the first pass as in the second pass?

I would like to save some time by turning the advanced options off in the first pass. And it's also usefull to use the same curve for a lot encodes of the same fragment with different settings for testing them.

I have also noticed that for the first pass, you don't have to set the right bitrate, unlike DivX5. So I thought: maybe counts that also for the advanced settings.

[akupenguin]

It's pretty safe to disable qpel and trellis in the first pass. Turbo does so automatically (along with several other speedups).

XviD's first pass uses constant quantizer, whereas DivX uses constant bitrate. That's (part of the reason) why XviD only needs two passes, while DivX doesn't get it right until the 3rd pass.

[pelle412]

The codec will automatically disable features that are not used in the first pass. I don't think there is a need to manually disable things for the first pass.

[Teegedeck]

Except if you define a zone with a constant quantizer in first pass (first pass at quantizer=3 is recommendable when you use high-bitrate matrices; generally you get better scaling if you define a quant that can realistically be reached to some extent in 2nd pass).

[mikeX]

akupenguin wrote
It's pretty safe to disable qpel and trellis in the first pass. Turbo does so automatically (along with several other speedups).

I believe it's 'Fast First Pass' that does that, not Turbo. Turbo should speed up certain calculations in QPel (and maybe GMC, can't remember).
In other words, disabling the settings you mention during the first pass is equal to enabling 'Fast First Pass', which is the default setting btw.
I'm not sure about Trellis, but Fast First Pass disregards at least the following:
VHQ, Q-Pel, GMC

There should be more in the xvid faq [see sticky]

[akupenguin]

yes, my bad.

[loni_blues]

For fast firstpass you can turn off Trellis, VHQ (also VHQ for b-frames), Chroma motion, GMC and Qpel.
Regards,
loni_blues

[sysKin]

Originally posted by akupenguin
It's pretty safe to disable qpel and trellis in the first pass. Turbo does so automatically (along with several other speedups).
Huh? Why would turbo do that?

The answer is: no, XviD knows quite well what to turn off and you shouldn't "help" it. Either you get everything right, and it's completely pointless (because XviD would turn it off anyway) or you get it wrong and you're in trouble.

[sysKin]

Originally posted by loni_blues
For fast firstpass you can turn off Trellis, VHQ (also VHQ for b-frames), Chroma motion, GMC and Qpel.
See? What I said above. What if he uses quant zones, have you thought of that? Turning anything off would screw filesize prediction, in such case.

[Teegedeck]

To clarify this: I believe in this case you mean using a quant-zone for only a part of the movie, for example credits.
When we were talking about quant-zones above, defining a single quant-zone for the whole movie was meant.

[loni_blues]

Thanks Teegedeck, that's what I meant. It's a workaround for doing the whole firstpass at q3 (when using high bitrate matrices) and not having to wait ages for it to be done.
Regards to all,
loni_blues

[ripper64]

I never use zones.