Gej's DivX Encoding Guidelines

[JimmyBarnes]

http://www.divx.com/support/guides/guide.php?gid=1

Written by: Gej
Valid for: DivX 5.0.2 and higher, DivX Pro 5.0.2 and higher
Last updated on: 2002-05-15

The purpose of this document is to give some guidelines on how to encode using the new DivX Pro 5.0.2. This document is not intended to be a tutorial or a how-to (despite its inclusion in the how-to guide section). It is assumed that the reader is an experienced DivX video encoder. Knowledge of the basics of video compression, of advanced encoding processes, and associated vocabulary is required to understand this document. This document was written by Gej, whose native language is French. Those of you who get hung up on minor grammatical and spelling errors on DivX.com pages and write us school-marmy emails about them are encouraged to jump in the nearest lake. ;-)

I'm told Gej is the programmer who created DivX. The guide sure sounds very authoritative. It's more on about the underlying WHY to use certain approaches.

JB

[ChAoS Overlord]

You can safely artifact-wise push the Psychovisual Slider to Strong

Is this true? If Psychovisual is so good by now, why isn't it in doom9's guides?

Global Motion Compensation, this tool will track the motion on a per frame basis, very useful for the horizontal or vertical panoramic and credits or anything with uniform movement in the frame. The encoding and Decoding CPU overhead is very small.

In DivX5, this also wasn't the case, is it true now? When playing back the same movie with or without GMC, what is the change is processor usage?

[theReal]

The only two parameters that can be changed (almost, bitrate accuracy may be degraded) safely between both passes are:
[...]
Pre Processing Source

This means I can make a first pass without temporal and spatial soften filters and safely run the second pass with strong temporal and spatial soften settings?????????

[Acaila]

Yeah, I find that rather odd too...

[Foambullet]

"Some parameters needs to be keep constant between the 2 passes to use Motion Vector Reuse:"

He is referring to settings that can be changed and still use the same Motion Vector file, not to bitrate accuracy.

[neo_sapien]

AVI output vs DivX MP4 file and advanced encoder features
Due to some limitations in the AVI file format itself and in the way the Video for windows architecture handle the video compression process, it not possible, for example to change the frame rate of the clip during compression, if input is 29.97 fps the output couldn't be 23.997fps, so telecide within the codec is not possible with the AVI file format, but these limitations does not apply with MP4 file format, the codec can crop/resize, change frames rate on the fly without any problems. So when source interlace is set to "all frames are telecine", an empty AVI is written and the telecined clip is written only in MPG4 file format.



Now, does this mean that MPEG-4 (.mp4) supports variable frame rates? If I encode a hybrid source with telecine, the output .mp4 file will be 23.976 fps at some points and 29.97fps at other times? This could be a breakthrough in processing hybrid sources with greater efficiency if possible. Can someone shed some light on this?

[DJ Bobo]

First and very important, keep the Data Rate Control (RC) parameters to default value, the codec behavior has been tweaked around theses values: they are the "sweet spot" of the codec.

Well I don't agree here, Max Quantizer on 12 is a way too much for my taste, I encode ALL my videos with Max Quantizer on 8 and there was no size issues. I got of course slightly better quality (visible!)

[JimmyBarnes]

Originally posted by bobotns

Well I don't agree here, Max Quantizer on 12 is a way too much for my taste, I encode ALL my videos with Max Quantizer on 8 and there was no size issues. I got of course slightly better quality (visible!)

Gej's comment seems to be in the context of using Psychovisual Enhancements - if you use quant 8 and say normal/strong PVE then the combo may overreact. That's my reading of it.

I also feel a bit uneasy about using Quant Max=12 even for a 1 CD rip - with DivX3.11a I always used 8 max, for 2 CDs max=6.

JB