Differences in quality compression between two movies

vbimport

#1

Something I don’t understand (I just bought DVD2oneX…).

I just compressed two different movies that have the same size (VIDEO_TS = about 7Gb) and I put each one on a dvd-r (so I choosed compression “Movie only” on 4,472 Gb.). Now I have one movie with very good quality and one with poor quality (big pixels in darkness, blur,…) why ?

I think I have choosen two different ways to extract the two movies (DVD Backup and OsEX). Could it be the reason ? Or are there other parametres for compression quality than the folder VIDEO_TS size ?

Thanks.


#2

it all depends on the original quality, DVD2one is for 100% relaible on that. Since it only compresses the material allready there.


#3

The quality of the two movies I was compressing with DVD2oneX were (as my eyes can see) as good as possible… I mean there is no difference in quality of original cinema movies I worked on…

so ?


#4

@ emaa°

It’s not the size of the VIDEO_TS folder, but the size of the movie .vob files, that you should be comparing.

For example, it’s quite possible to have two DVD’s with a VIDEO_TS folder of 7gb, but the movie .vobs on one may be 6.8gb and on the other 3.8 gb.
The compression on the first one would be significant, but on the second, not necessary, hence the difference in quality.


#5

there was no difference… the vob files have about the same size for the two movies…

in fact, the poor quality compressed movie has a lot of dark scenes and there I can see big pixels… but anyway all the other scenes are poor quality comparing to the other compressed movie…

strange ! I don’t understand.


#6

Maybe it depends on the bitrate of the original…


#7

@emaa°

Even on different movies of the same file sizes, the degree that each is compressed won’t necessarily match up. Consider the overall length of the film, for example. For arugment’s sake, lets say that you’re comparing Pearl Harbor to First Blood. (This is ONLY for the sake of argument, guys!) Let’s further assume that both movies have the same file sizes. Pearl’s close to the three hour mark. Blood’s only 90 minutes.

If First Blood was encoded using a high bit rate, you’ll be able to whittle away at it quite a bit before really noticing very many defects in the copy. That’s because there’s more picture information present than there would have been with a lower bitrate. Therefore, you’ll have a better result if this is the movie you’re copying (again, keeping in mind that I’m being hypothetical).

Let’s say that Pearl Harbor uses a fairly low bitrate. (To fit on the same size of file as First Blood, it’d have to!) Since you don’t have much to chew on, ANY reduction is going to be obvious.

But it’s entirely inconcievable to have two movies with very different content (more dark areas, action scenes, ect), different lengths, and different overall bitrates, seem like they’re the same when all you’re viewing is the file sizes. The file size only states the volume of information that they contain, as it applies to whatever will be reading them. It doesn’t really provide much of an indicator as to properties of the content.