Single Pass Encoding

[twipley]

this was written in the log (default settings xvid encoding):
[3/1/2009 12:34:02 PM] Running single pass encoding.

but, i've read that "two-pass does a much better job at evenly distributing bits where they are needed and therefore gives you a much better looking end result." source: http://www.gromkov.com/faq/conversion/xvid_options.html

any logical reason single pass is being used?

thanks,
twipley

[tamilan09]

Two pass encoding does a better job at keeping the video at a file size limit and still maintaining a good quality. Single pass, however, still maintains a good quality (with target quality percentage above 75%) but doesn't have file size limit. I personally use single pass encoding as I don't care much about file size. Unless your ripping the dvd to a 1.4gb or something, you will need to use two pass encoding. Quality is not a issue with both encoding.

[twipley]

oh, alright, thanks for the fast answer. so because i told it to "not limit the output to the size of a cd, but instead focus on the quality (75%)," it decided to go first single pass.

in other words, if i understand right, when you don't care about size, pick desired quality (75% seems recommended here), and the end result will still look good, even if it's not a two-pass encoding. so in that respect, single-pass encoding is still recommended.

sounds fair to me. :helpful:

[tamilan09]

Yes 75% is good but if you don't care about file size like me, I would use 85%+ which should give really good quality. Also use Advanced settings to make sure audio bitrate is low (around 128-224). And maximum width is around 640.

[twipley]

yeah, but i've heard over 80% to be an overkill, as for higher (e.g. 100%), file size almost doubles from 67%, but quality increase in output is barely, if at all, noticeable. that's why i've just (oh wait, i'm still) re-encoding the videos i had encoded last night.

just my two cents, and also something you can try on your side. ;)

[BigDid]

...
but, i've read that "two-pass does a much better job at evenly distributing bits where they are needed and therefore gives you a much better looking end result...
any logical reason single pass is being used?

Hi,
True, 2 pass does a better job ratio size/quality at the expense of time.

So if you don't care about size, or care about time go original width, 1 pass 100% quality.

When I want to keep full width, I do 1 pass/75% to get an idea of final size, original width movie.
Giving the resulting size, I will go for a little less size+audio and usuallly have no need to redo a full 2pass encoding.

yeah, but i've heard over 80% to be an overkill, as for higher (e.g. 100%), file size almost doubles from 67%, but quality increase in output is barely, if at all, noticeable...

Well, it is all about your preferences and output quality; depending on your display, 80% may feel good enough; for a big LCD tv you may want to get the max quality, even disable B-frames for less difference with the original (only attainable in 2 pass mode)...

Yes 75% is good but if you don't care about file size like me, I would use 85%+ which should give really good quality. Also use Advanced settings to make sure audio bitrate is low (around 128-224). And maximum width is around 640.
Hmmm, I can go to original width (720) in 1 pass without problem. Why limit audio quality if you don't care about size? keep original or go for a good Mp3/Abr encode (192Kbps or more)

Did

[weaver4]

When you are doing two pass you really don't know what filesize or bitrate to set it to. Some movies do great at 700kbps and others need as much as 1.5Mbps; for the same size movie. The bit rate that you need can vary widely depending on the movie; how much action it has, how many dark scenes, how much grain. For example I have one movie that has a lot of action in a Jungle, so the leaves are always moving (as the camera pans) and it requires a "Truckload" of bitrate to make the movie look good.

I believe you get a better quality movie with Single Pass-Constant Quality than two pass. The reason for this is the codec can do a better job of setting the bit rate automatically using CQ than you can manually.

You could encode a movie in single pass then look at the filesize and then do two-pass to get the same filesize, but I have tried this and I don't see any change in quality, so I don't think it is worth the effort.

[manono]

but, i've read that "two-pass does a much better job at evenly distributing bits where they are needed and therefore gives you a much better looking end result." source: http://www.gromkov.com/faq/conversion/xvid_options.html

any logical reason single pass is being used?
That guide is referring to single-pass Constant BitRate (CBR) encoding, and the guy is absolutely right about not using it.

When doing single-pass encodes using AutoGK it's using Variable BitRate (VBR) encoding, which has nothing to do with what you or that guide mention. AutoGK's Target Quality is very close to the Single Pass-Target Quantizer of XviD, about which the guide writer says almost nothing at all, and which he doesn't even seem to understand. When, in conclusion, he says, "Always use two-pass encoding" and, "Only use target size, not target bitrate or quantizers", he couldn't be more wrong.