Xvid Setting: 1pass Quantizer vs Bitrate Mode, vs 2pass => Quality

[carlaron]

Hello,

I have done some search around the net and throughout different boards, still I couldn't really find an answer to my question.

My situation: I am converting old analog and digital videos to XviD. (cam films, different quality, different content)
My goal: above average quality with a little weight on file size (primary quality goal); no time limit
Also: same settings for all files! --> batch

Testing out many different XviD settings, I still have problems deciding on the 1pass or 2pass method.
So far I am settling on 1pass Quantizer 4 setting.

What I want to know is, what the Quantizer setting really means; my understanding is that it sets the Quality (and bitrate, etc. are varied to meet the criterion)

On the other hand, many sources say, that 2pass is the best option, but what bitrate do I have to choose then? since my goal is not a fixed file size; and many clips are very different in content.

Is there any gain for me over the Quantizer setting? is there anything similar in the 2pass mode? how can I gain from 2 pass mode? Any details on Quantizer 1pass mode?

Thanks

[jagabo]

Target quantizer mode uses a fixed quality for each frame. The lower the quantizer the higher the quality. Think of the quantizer as how much data is being thrown out.

In target quantizer mode you pick the quality but you don't know what size the file will turn out.

In 2-pass VBR mode you pick the file size (file size = bitrate * running time) but you don't know what the quality will be.

In general, they are flip sides of the same coin. You use bitrate mode when you want a file of a fixed size. Say, a 700 MB file to fit on one CD. You use quantizer mode when you want a file of known quality.

There are a few advantages of VBR bitrate mode. The bitrate caps indicated by the Profile Level are respected. So if you have hardware with bitrate limitations you may want to use that mode, especially when working at high quality levels. And at low quality levels VBR can be a little better at distributing quality. For example, a camera flash going off might cause one frame to be much brighter than the others. Quantizer mode will use more bitrate for that frame because it blindly encodes all frames with the same quality. But in VBR mode the codec knows that you won't really notice if that one frame is encoded at a lower quality. The disadvantage or 2-pass VBR mode is that it takes twice as long to encode.

[carlaron]

thank you!

from what I understand now: Quantizer setting gives me what i want: a certain, set quality.

but you also suggest using a 2pass version could add value in terms of smaller file size, is that correct?

if so, how do I translate a quantizer of e.g. 4 into a 2 pass setting?

[jagabo]

but you also suggest using a 2pass version could add value in terms of smaller file size, is that correct?

2-pass has a very small advantage in perceived quality (at normal playback speed) when the two methods give the same file size.

if so, how do I translate a quantizer of e.g. 4 into a 2 pass setting?

That's the problem. You can't, really. Every video is different. Here's a link to a comparison I did to demonstrate this a while back:

https://forum.videohelp.com/topic357646-60.html#1903520

One video required 20 times as much bitrate as the other to maintain the same quality. Of course, real world video don't reach either of those extremes but it's quite easy for differences to vary 2 fold or more. Bitrate requirements vary depending on frame size, frame rate, noise (snow), action/motion, brightness, etc.

[carlaron]

so the real problem is: there is no feature like 'average quality' that could be used in a two pass setting to reduce file size.

any suggested workaround, or should I stick with the 1pass quantizer setting?

[jagabo]

Take what you think is a typical video, encode it at whatever quantizer you are happy with, then examine the bitrate of the resulting file with GSpot. I use Target Quantizer = 3 for "watchable" video, 2 for more important stuff.

[charingyu]

Could I please ask a question?

is there any way to convert the Target Quantizer (single pass) to Bitrate setting?
I'm using this coverter WinAvi 10.1, but 10.1 doesn't allow me to set my Xvid codec with the Target Quantizer mode and I can only do it with Bitrate. I usually set my target Quantizer to 5.09, is there like an equivalent for bitrate?

thanks

[manono]

If you understood what jagabo was saying earlier then you would know the answer to your questions is 'No'. An easy way around your problem is not to use WinAVI (which isn't any good to begin with). Use Virtual Dub instead, or some all-in-one program that allows for quality settings. One such program is AutoGK set up in 1-pass Target Quality mode.

[charingyu]

Thanks for the quick reply!
VirtualDub doesn't open the file i need to convert, an mp4 file :P

I'm try AutoGK when I get home.
Thanks again

[jagabo]

VirtualDub doesn't open the file i need to convert, an mp4 file

Do you have an MP4, Quicktime, or DirectShow source plugin for VirtualDub?

[manono]

AutoGK won't work either. Sorry, I didn't know it was an MP4. Of course, one might wonder why convert an MP4 to AVI. Maybe it's for a standalone DVD player that also plays XviD/DivX AVIs.

XviD4PSP will do the job. In the Video Encoding Settings set it up for Constant Quality at whatever quantizer you like.

[charingyu]

VirtualDub doesn't open the file i need to convert, an mp4 file

Do you have an MP4, Quicktime, or DirectShow source plugin for VirtualDub?

I extracted this https://www.videohelp.com/download/VirtualdubPluginPack.zip to the folders in VirtualDub, and I can open the mp4 file.
But I get a black screen, and when you do Xvid convert it's still gives u a black screen.

I tried selecting the file type when I open the video to QuickTime Video Files *.mp4, and it gives me a green screen

am i still missing something D:
------edit-------
Thanks I put in the DirectShow (DShowInputDriver-0.5), and I selected that from the file type and open my mp4 file and it worked !!!

and
@manono
thanks for that recommendation, but the conversion speed is like 6 hours for me, but I kept it incase the virtualdub method fails too. Thanks!!

[jagabo]

I extracted this https://www.videohelp.com/download/VirtualdubPluginPack.zip to the folders in VirtualDub, and I can open the mp4 file.
But I get a black screen, and when you do Xvid convert it's still gives u a black screen.

I tried selecting the file type when I open the video to QuickTime Video Files *.mp4, and it gives me a green screen

am i still missing something D:
------edit-------
Thanks I put in the DirectShow (DShowInputDriver-0.5), and I selected that from the file type and open my mp4 file and it worked !!!

You can also try using the "Ask for extended options..." option on the File Open dialog, then try the different options in the Quicktime or MP4 source filters.