difference between 2 pass and x pass

[burnix]

Hello.

I just want to know if there is a difference between 2 pass and x pass.

In my mind the first pass was the pass to establish log file and the second use this file to optimise the encoding.

Someone can explain me the advantage of x pass, because if youy do a good analyse of the video on the first pass, you dont have to do much work.

Thanks for all your response.

[Awatef]

Well, theoretically you can increase quality with more than 2 passes, but it won't be as noticeable as with 1-pass compared to 2-pass.
Most tend to agree that there is nothing extra to get from more than 3 passes.

I personally use 3 passes only when the movie I'm encoding is very important and needs every bit of quality it can get (and that's rare :D)

[Sharktooth]

3 passes dont necessarily increase quality.
The 3rd pass refines the bit allocation thru a more accurate rate control, so in some cases may increase perceived quality by keeping the quality more consistent across the encode.
However it may also be that 3 passes just do not significanlty improve the bit allocation at all.
So, in practice, the 3rd or nth pass account from the inaccuracies of the DivX rate control in the previous passes.

[weaver4]

Well, theoretically you can increase quality with more than 2 passes, but it won't be as noticeable as with 1-pass compared to 2-pass.


Most people can not see any differance between 1-pass constant quality and 2-pass for the same filesize. There is a huge differance between 1-pass constant bit rate and 2 pass, but not 1-pass constant quality.

[numaios]

Most people can not see any differance between 1-pass constant quality and 2-pass for the same filesize.
And how do you match the exact fixed quantizer without having to encode several times before you get your desired file size?

[Awatef]

Well said numaios :D

[weaver4]

And how do you match the exact fixed quantizer without having to encode several times before you get your desired file size?

Single-pass cq is for those of us that don't care about filesize. We want a specific quality but don't really care how much room it takes on our harddrives or DVDs.

What I was saying is encode a movie using a specific quantizer (say of 3). Get the file size from the result and then use this as a target filesize for two-pass and you won't see much, if any, difference in quality.

The problem with two-pass fixed-filesize is that you can't guess what filesize is needed to get a good quality movie. Sure you could guess at 1300kbs, but Casablanca needs 1500kbps to get a good quality movie and Firewall requires 950kbs.

[numaios]

Single-pass cq is for those of us that don't care about filesize.
In that case, I agree with you.

What I was saying is encode a movie using a specific quantizer (say of 3). Get the file size from the result and then use this as a target filesize for two-pass and you won't see much, if any, difference in quality.
But in that case you have plenty of bitrate, so of course you won't notice any difference.

[burnix]

Thanks for all.
I just start to encode with ffmpeg and mencoder (i compile under mingw+winxp).
Those encoder are really good, but too many parameters.

Thanks.

[Brother Darrell]

Quality is a relative term..ya know? are you playing back on a 21" monitor or ar 61" Mitsubishi? A good general rule of thumb(at least from my experience) 2.8 is a good quanitizer To go with. both as 1st pass & second pass. You also have to consider encoding size. I like to encode at 1024x(1.88 or 2.35) 3.45 works just fine(2 pass by the way... bitrate distrbution is everything)

Nothing I say is original. I just repeat what I tried & liked.

[Awatef]

O-Oh! encoding at 1024x from DVD sources is a big NO NO my friend, you're just wasting your time and your bitrate...

[sarmin]

i use qantizer 4. do you think that is good or should i use 3?

[Blue_MiSfit]

sarmin, if it looks good to you then you don't need to lower the quant.

I dont care which quantizer you use :)

All that matters is how it looks to you.

Now, if you are going to upgrade your display device in the near future, I would suggest bumping it up a bit :)

Keep full resolution if you aren't allready, and also consider XviD with a CQM or x264 !

~MiSfit

[ChaosKing]

With which mode I would get a better Qualiy, Constant Quality or a Constant Quantizer, if both have the same File size.

[Brother Darrell]

O-Oh! encoding at 1024x from DVD sources is a big NO NO my friend, you're just wasting your time and your bitrate...

Why is that?
My projector is highdef 800x600. Using it as a monitor, hooked up to my computer (Bubba style htpc :D )
works just dandy.

[Brother Darrell]

O-Oh! encoding at 1024x from DVD sources is a big NO NO my friend, you're just wasting your time and your bitrate...

What I really was trying to accomplish was a decrease in blockiness, since anything playing back at high density would, by it's very nature, be increased anyway(stretch & pull), to make it fit on the screen. My reasoning for encoding at a higher resolution is to eliminate , (or at least minimize,) blockiness.
So..Increasing the h/w, from 720x to 1024x does NOT increase resolution because you can't encode pixels which do not exist. I follow that.

I'm sure this has all been discussed before somewhere. Is there a thread with more on this subject?