DVD Shrink generates different files even with the same settings

[sldvd]

I just did a little bit of experimenting in DVD Shrink. I compressed a DVD to the hard drive, and then I compressed the same DVD to a different folder on the hard drive, using the exact same settings. I used a comparison tool to compare the 2 folders, and the contents were different (although exactly the same size)! I did the same experiment with another DVD - compressed it twice to 2 different folders using the exact same settings, and the files in the 2 folders were different (but the exact same size). Wonder why DVD Shrink is generating different content every time, even with the same settings?

[VirtualDoobMon]

different how??

[sldvd]

The 2 folders have the same files, and the files are the same size, but the content of the files is different. If you do a binary comparison of the files, you can see they are different.

[kpa]

I don't think that's surprising in any way, VOB/IFO files contain some metadata that includes stuff like compilation date etc. which means that every time a new VIDEO_TS folder is created from same source with same settings the resulting files will be slightly different compared to previous ones.

[sldvd]

These aren't just a few differences, according to my diff tool it looks like there's thousands of differences. Another thing is that when I use TMPGEnc MPEG Editor to create DVDs, if I create the same DVD twice and then compare them, there are absolutely no differences. I guess each program goes about generating DVD files in different ways.

[TJohns]

TMPGEnc is an "encoder" - it takes a given source frame & re-encodes it. This is a very deterministic process (i.e. reproducible) and so you'll get the same output each time.

DVDShrink is a "transcoder" - it takes the source STREAM (i.e. the MPEG2 encoded video track) and tries to work out which parts is can remove with the least visual effect (quantising colour channels, duplicating nearby pixels, etc). I can imaging that this process might invoke a certain number of "random" decisions - like which pixels to dither in a background scene - and this random number generator may mean each time you run the process you'll get differing results!

Trevor

[sldvd]

I guess that makes sense. I wonder if anyone would actually be able to tell the difference between two different DVD Shrink outputs on the same source with the same settings?

[jagabo]

Multithreaded tools performing non-deterministic calculations often deliver different results.