Reusing first-pass log-files?

[andreaskorth]

Hello!

Under which conditions is it possible to reuse the log-files (and mv-files from DivX 5) for a second-pass encoding with different parameters?

From my naive understanding you should be able to reuse them if the resolution is changed (at least when it's lowered). Even if different cropping is used (a few pixels) there is no essential change to a frame's complexity.

Any experiences?

[khp]

Presonally I don't like changing any thing at all, why take any chances, when you can do a new first pass in a few hours ?

Slight changes in bitrate may not cause much problems, but I think changeing the resolution is probably a bad idear, especially if you use the mv log file. The mv log file logs motion vectors, if you change the res, the coordinates specified in the log will nolonger be valid, this may well result in massive artifacts.

In the case of the normal logfile, it logs image complexities, these will also change when you change the res, but this will happen on the same scale for all frames, so you might not get any serious problems with the divx.log file.

[andreaskorth]

Well, I'm an impatient person not willing to spend a few extra hours on a first pass if it isn't really necessary.

But you're right, motion vectors become useless if you change resolution/cropping.

I was just doing some tests on the pink artifacts problem in DivX 5 to figure out how it is affected by different resolutions (%16, %8, etc). I just didn't want to wait two hours for the first pass every time.

Sometimes, though, I create two versions of one movie. A harddisk version in full resolution, maximum quality and a 1-CD-rip for "mobile" use.

[khp]

Originally posted by andreaskorth

I was just doing some tests on the pink artifacts problem in DivX 5 to figure out how it is affected by different resolutions (%16, %8, etc). I just didn't want to wait two hours for the first pass every time.

For testing I usually just use 1-pass quality based encoding.

Would you mind posting your results on the pink artifacts with mod 8 etc ?, I know mod 16 works. But afaik macroblocks are 16*16 pixels (don't remember where I got this from), so I am curious to know if mod 8 also works.