1st & 2nd pass in BDRB...

[Lathe]

Hello!

I think this one is pretty simple, but this was brought up on JDobbs BDRB 'bug report' 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!

[jdobbs]

Here's what MeWiki says about it:slow-firstpass
Default: Not Set
Using --pass 1 applies the following settings at the end of parsing the command line:
--ref 1
--no-8x8dct
--partitions i4x4 (if originally enabled, else none)
--me dia
--subme MIN( 2, subme )
--trellis 0
You can set --slow-firstpass to disable the feature, set this option. Note that using --preset placebo enables slow-firstpass too.That would imply that you don't have to repeat --ref, --me, --subme, or --trellis in your pass-1 tweaks.

[Lathe]

Hey JD...

That was really nice of you to take the time to answer this; sure appreciate it!

Sorry, I didn't quite understand though... assuming I use BDRB's default 'High' 2 pass setting, can I still add these tweaks JUST to the 2nd pass like I've been doing...?

What do you think about the further parameters that I use also? Here is the complete set of Tweaks that I would normally 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

Thanks again!

[jdobbs]

I'd have to look at each carefully to give a good answer. But, if it's not one of the ones listed as set by "--pass 1", I'd put it in both tweaks.

[Sharc]

...But, if it's not one of the ones listed as set by "--pass 1", I'd put it in both tweaks.
Exactly.
It's so simple to put these into both tweaks just to be on the safe side. Probably one would have to check for each and every parameter if and how it affects the stats file, and how sensitive deviations between pass 1 and 2 are to the final result. Although x264 seems to be pretty robust with relaxed settings for the first pass, I'd be very careful with parameters which change the encoder characteristic, like --qcomp and --direct (see Dark Shikari's et al. reply in the link I posted in the bug reports thread).

[Lathe]

Thanks kindly to both of you. That gives me something to go on...

*** EDIT

YES, the one thread was very helpful indeed. I still don't know exactly how BDRB sets the --direct on the first pass, but DS did make quite clear that if there is no data retrieved on the first pass, then --direct auto only on the 2nd pass will default to 'temporal' which is of poorer quality. Heh, the one guy asking something similar to what I'm asking here was SO persistent in getting details, that finally I think the others covered just about every other parameter that needs to be the same between both passes. From what they said, it doesn't SEEM like any of the other parameters NOT being set in the fist pass (well beyond whatever BDRB sets them I suppose) shouldn't affect the quality of the 2nd pass results.

So, either I need to find out how BDRB sets the default first pass --direct parameter OR probably simpler, like you said above Sharc, just add the first pass tweak: --direct auto, that way I would think I'd be covered.

***EDIT 2

Looking further concerning the qcomp setting, since it's definition is to decide where to place more bit rate (qcomp-0 would make slow scenes look perfect and high motion scenes look terrible - qcomp-1 would provide constant quantization which theoretically will look good, but cost a lot of bitrate in slower scenes where it is not needed) So, since I would GUESS that since the whole point of the first pass is to gather data, then I am thinking that I should also include a first pass parameter for that too, matching the 2nd pass. Wouldn't that then tell the encoder to LOOK at these areas with the qcomp=.5 in mind on the first pass? Or am I getting a little esoteric here...?

Thanks again!

[Lathe]

Ah, I found this post from you Sharc on another thread here:

For BD5 I used "--preset medium" with the tweaks me=umh and subme=8. It didn't add too much encoding time. Any stronger/higher settings did not really pay off, IMO.

Basically, I do the same thing with the encodes needing higher compression. I think JD uses 'medium' settings for the 'High Quality' encode, so I bump these exact parameters the same :) I don't use the 'Very High' setting on BDRB because I think it uses subme=9. And there is a frigg'n HUGE jump in encoding time for what I feel is no real discernable difference.

[Sharc]

I did these tweaks in the context of BD5 backups where very high compression is needed, and I included them for pass1 and pass2, also to keep them alive for CRF single pass encodes as well.

The tweaks and "moving some bits from here to there" discussion become pretty much pointless IMHO for high-bitrate backups on BD25. Why not use BD-RB's defaults or automatic settings? Have you ever found any real, visible reason?
Well, placebos come in various flavours ..... :D

P.S.
Never mind, but kindly read the forum rules about using bold text :)

[jdobbs]

I did these tweaks in the context of BD5 backups where very high compression is needed, and I included them for pass1 and pass2, also to keep them alive for CRF single pass encodes as well.

The tweaks and "moving some bits from here to there" discussion become pretty much pointless IMHO for high-bitrate backups on BD25. Why not use BD-RB's defaults or automatic settings? Have you ever found any real, visible reason?
Well, placebos come in various flavours ..... :D

P.S.
Never mind, but kindly read the forum rules about using bold text :)A lot of time and effort went into those settings. Trying to keep adding improvements at BD-25 bitrates is kinda' like masturbation. It might make you feel good -- but it really doesn't accomplish anything. The same is true for any x264 settings above "medium".

But... I add the TWEAKS setting specifically because there are a lot of people out there that "feel" as if they can improve them.

[Capsbackup]

Trying to keep adding improvements at BD-25 bitrates is kinda' like masturbation. It might make you feel good -- but it really doesn't accomplish anything.

Well there might be some disagreement to the accomplishment part! ;)

[Lathe]

A lot of time and effort went into those settings. Trying to keep adding improvements at BD-25 bitrates is kinda' like masturbation. It might make you feel good -- but it really doesn't accomplish anything. The same is true for any x264 settings above "medium".

But... I add the TWEAKS setting specifically because there are a lot of people out there that "feel" as if they can improve them.

LOL! That's great Jd :) Yeah, you are probably right. I think the key here, and you have mentioned it many times, that at this high of a bit rate, these changes (tweaks) probably are not even discernable. That's why I DO kind of smile when many here go to the extreme lengths of using 'Very High Quality' or 'tesa' and similar placebo settings. I guess that I just thought I could throw in a few 'improvements'. But, you are right I think, it probably just makes me feel as though more of the movie quality is being preserved.

I suppose that such things and settings are really more for people who have to enode things in smaller files or at lower bit rates. THEN, these kinds of settings probably really make a difference.

Appreciate your patience though and thanks for your input!