BDRB - 1st & 2nd pass x264 settings

vbimport

#1

Hello!

Been a while since I’ve been here :slight_smile:

I think this one is pretty simple, but this was brought up on JDobbs BDRB forum and I wanted to get some (more experienced) opinions here, if I could please.

What I’ve been doing for quite a while with BDRB is where the Blu-ray size is pretty big (say over 30 Gigs) and I am reducing the size to fit on a BD-25 (which in actuality is really about 23.x Gigs) I normally set BDRB for ‘High Quality’ ‘2 pass’, and since the settings that JDobbs uses are a tad low (in my lowly and wretched opinion) what I’ve been doing regularly is using x264 ‘Tweaks’, but only on the 2nd pass. These are the tweaks that I usually use:

TWEAK_PASS_TWO=–ref 4 --deblock -2:-2 --psy-rd 1.00:0.20 --me umh --subme 8 --trellis 2 --direct auto --qcomp 0.50

I do that basically just to tune a bit more for a sharper image (film) and bump up the other settings just a little (qcomp basically moves slightly more bits to static scenes from high-motion scenes - suggested by Selur, the creator of Hybrid) Now, if the compression is not going to be that high (say the original Blu-ray size is like around 26 Gigs or so, for example) then I just use these tweaks:

TWEAK_PASS_TWO=–deblock -2:-2 --qcomp 0.50

But, when I mentioned this recently, one of the guys replied that if I tweak just the 2nd pass settings and don’t match the 1st pass the same (such as the Deblock setting, for example) that I could be doing more harm than good.

This was a COMPLETELY new thought to me, because I just ASSUMED that any important tweaks would be done just on the 2nd pass. BTW, I THINK that BDRB uses ‘fast 1st pass’ as a default.

Am I wrong on this, do you HAVE to match some or all of the settings for BOTH passes…???

Appreciate any input on that, thanks!


#2

qcomp basically moves slightly more bits to static scenes from high-motion scenes
Isn’t that exactly backwards from what is needed? Static scenes tend to need less bitrate.

As to matching settings, I have no idea if it is absolutely necessary, but I can’t see that it would hurt except in speed. First pass with any of the mpeg/mpeg4/h264 encoders when doing a multipass encode is generally mapping out the movie, finding the areas that need more bitrate or application of the encoding parameters.


#3

[QUOTE=Kerry56;2772187]Isn’t that exactly backwards from what is needed? Static scenes tend to need less bitrate.

As to matching settings, I have no idea if it is absolutely necessary, but I can’t see that it would hurt except in speed. First pass with any of the mpeg/mpeg4/h264 encoders when doing a multipass encode is generally mapping out the movie, finding the areas that need more bitrate or application of the encoding parameters.[/QUOTE]

Hey, thanks for the fast reply!

Hmmm, yeah… I’ll hafta do more reading on that. What I thought was happening was, as you say, the first pass is scanning it for the information about how best to optimize the film’s encode in the 2nd pass. To me it seems that by adding specific tweaks for the 2nd pass, you are merely TELLING it specifically what to do on the 2nd pass for these parameters. And, the whole point is that the parameters that I am supposedly tweaking are higher settings. So, it would SEEM to me that at most you would be superseding the lower parameters that the first pass would ‘determine’ anyway, right…?

As far as the qcomp setting, Selur explained that since your eye does not notice details in high action scenes, but it DOES in more static scenes with less movement, then, technically, buy giving the parts where your eye CAN see more detail is supposedly better. Kind of makes sense, I think… :slight_smile:


#4

Sorry I’m late to the party
Match the tweaks in the first and second pass
The first pass is basically figuring out the bitrates based on your settings.
The second pass does the encoding, so try to keep the same settings just to make sure the size comes out right
Not matching — does it hurt, probably not
Matching — does it hurt, no


#5

[QUOTE=gonca;2772897]Sorry I’m late to the party
Match the tweaks in the first and second pass
The first pass is basically figuring out the bitrates based on your settings.
The second pass does the encoding, so try to keep the same settings just to make sure the size comes out right
Not matching — does it hurt, probably not
Matching — does it hurt, no[/QUOTE]

Okay, let me see if I understand this…

‘Not matching’ = doesn’t hurt

‘Matching’ = doesn’t hurt

‘A large, beautiful, blonde muscular woman tying me up and beating me’…

…hmmm, I think I found my choice… :cool:

Heh, seriously, thanks!


#6

Not matching probably wont hurt — Maybe
You could, however, run into setting conflicts or improper sizing because of it
Matching the settings costs nothing and you avoid potential issues


#7

[QUOTE=gonca;2772901]Not matching probably wont hurt — Maybe
You could, however, run into setting conflicts or improper sizing because of it
Matching the settings costs nothing and you avoid potential issues[/QUOTE]

Yeah, I agree; I am doing that now.

Thanks!