Nandub and Fast/Normal recompress

[bengalih]

Hi all,

I am using nandub to encode 1080p .TS down to 720p using DivX 3.11.
My sources tell me that DivX 3.11 with Nandub is best for my application (xbox - limited CPU power) because it allows a maximum bitrate to be set PER FRAME (with SBC options) as opposed to maximum average bitrate which might exceed what the CPU can handle.

In any event, this seems to work pretty well, but I am getting strange artifacts in my opening credits (on the lettering). I find this only happens with "Fast Recompress" and not "Normal."

I am trying to understand what the disadvantages of "Normal Recompress" are. Do they lose YUV info, even in the newest versions? If so, what can I do to get rid of these artifacts while still retain YUV? In other words, what is Normal doing to preserve the quality that Fast fails to do, and can I do another procedure to preserve both quality and YUV.

thanks!

[mic]

Try using V/dub or mod

[setarip_old]

I am trying to understand what the disadvantages of "Normal Recompress" are.

Slower...(But, in this case, slower=better)

[bengalih]

Thanks for the replies guys, but I can't use vdub or vdub mode because they lack the SBC for DivX 3.11 that nandub has.

Also, I know that the Normal is slower, and as explained, it is obviously better since I lack artifacts with Normal.

What I am looking for is some slightly more technical info on what "Normal" does and "Fast" does not (and vice-versa). Also, as stated I read bits and pieces of how they alter the color space, and am looking for that specific info as well.

thanks!

[setarip_old]

This link may provide you with the insight you're seeking:

http://www.videohelp.com/forum/archive/t145121.html

[bengalih]

Thanks, that does have some useful info, I will quote here to make easier:

For some reason nobody here seems to know what the different processing modes in virtualdub do.

IF you are converting something from mpeg1, 2, any divx codec or variant thereof, and anything other than uncompressed rgb or huffyuv in rgb mode, and not doing any filtering in vitualdub, you should use FAST RECOMPRESS mode.

When you are converting from a RGB source, or using virtualdub to filter the video, are the only times you should use Full Processing mode.

Why? It's simple really, any of the above mentioned formats other than RGB operate in the YUV colorspace. Virtualdub's Fast Recompress mode also operates in YUV, as opposed to Full Processing which operates in RGB.
Thus, when virtualdub is say encoding an mpeg2 file off a DVD into XviD, in fast recompress mode the video is staying in the YUV colorspace from source to encode. When vdub is in Full Processing mode the video is going YUV -> RGB -> YUV. This is bad because it A. Slows down the process alot due to converting between colorspaces, and B. degrades the quality of the chroma planes causing color bleeding and such.

Keep this in mind when writing guides for the site, helping others, and doing your own encodes.

Now, based on that info, can anyone suggest a reason as to why Fast Processing causes artifacts when converting HD, and why Normal Processing does not? Even better, any other settings I might tweak in Fast Processing that might have control over that?

[stephanV]

(Screenshots would be helpful)

I assume you are frameserving from AVIsynth... maybe DivX codec does a faulty conversion with the colorspace you are serving it and it is handling RGB24 (converted due to Normal recompress) correctly.

[bengalih]

yes, from an .avs created in GK.

I think you are probably right, with DivX 3.11 being so old that it isn't handling the high resolutions properly. It's a shame, because it is the only codec that we can implement SBC with (via nandub) to ensure a maximum bitrate per frame.