DVD Shrink and the .vob filetype question

smurph wrote on 9/3/2004, 8:47 AM
Hi all --

Someone took a dvd-r movie I made and extracted it from the dvd to their hard drive using DVD Shrink. I don't know why they did that, but I guess they assumed one needed to extract a VIDEO_TS folder using some kind of software in the same way that one would need to extract .wav files from an audio cd.

End result is the file sizes have changed -- all the .vobs including the menus. The main 1GB .vobs are again all equal to, but larger than, the originals, and the remainder .vob is smaller. Plus it appears to be slightly smaller overall -- maybe 50KB out of the 4.2GB.

They used the feature called 1:1 copy, which according to the info I have been able to locate, purportedly generates an identical fileset. I have my doubts, though. I believe that particular feature is used for extracting only the main movie (which might fit on a dvd-r) and leaving behind the extras, outtakes, etc.

Question for any experts is "has it been recompressed," or can an app like DVD Shrink take the underlying mpeg2 from within the .vob wrapper and shuffle it around to regenerate the .vob files only, leaving the original mpeg2 (and associated audio) essentially untouched?

It has an .ac3 5.1 soundtrack if that makes any difference. I do not know how long it took the program to create the new VIDEO_TS folder, whether it was minutes (good sign) or hours (bad sign).

Any one? Thanks.

Comments

johnmeyer wrote on 9/3/2004, 9:18 AM
I don't think DVD Shrink changes the bitrate. Here is a description of how it works:

FAQ about the Transcoding Technique
rmack350 wrote on 9/3/2004, 10:57 AM
50 KB isn't much over a 4GB+ set of files. Could this be a difference in the way the disks report their usage? Maybe a difference in cluster sizes or something?

Rob Mack

smurph wrote on 9/3/2004, 12:48 PM
Thanks for the link, John. That's a boatload of info.

I decided to do this myself, and compare the q-level and bitrate differences between the original and the re-code. Both were done under XP Pro. The Full Backup took about 7 minutes, so the transcode went quickly.

Using Bitrate viewer, we see a large difference across the last .vob file, as much as 1.5M in the bitrate at some points. In both cases, the q-level fairly tracks the bitrate, but is just as relatively different across the timeline. I don't know how to post this jpeg right now, which shows the differences superimposed.

I think it might be fair to say it is just not the same file anymore. I'm surprised, and curious to see if there are any visual differences. I do not have a viewer at this time.

From the description, one would have imagined that the q-levels would stay roughly the same, as no bitrate reduction would theoretically be necessary during the 1:1 transcode. But the Bitrate Viewer tells otherwise.

B.Verlik wrote on 9/3/2004, 12:54 PM
I've been told that you should go into 'compression settings' and click the 'No Compression' and don't let it sit on 'Automatic'. Even though it seems like it shouldn't make a difference.
smurph wrote on 9/3/2004, 1:12 PM
Rob, I was wondering that too. The 50KB number was reasoned from indirect info. After doing the transcoding myself, here's the breakdown:

Size is 12288 bytes smaller
Size on disk is 4096 bytes smaller. (cluster size)

Now, 12288 = 4096 x 3. So, over 4GB+ folder size, there is just a cluster-sized difference between the two. Missed one frame, maybe.

Interestingly, here's the breakdown for the 95MB menu .vob:

Size is 288 bytes smaller
Size on disk is 12288 bytes smaller. (why the x 3 factor?)

So it's a cluster-size phenomenon, and I suppose one could interpret this to mean that both folders contain the same amount of info, just somewhat mis-reported? However, the .vob's were certainly altered (see post above).

Thanks for pointing in this direction, Rob.
smurph wrote on 9/3/2004, 1:19 PM
Steve,
Yes this was done with "No Compression," which seems equal to that slider being up at 100% for "Custom Ratio" as well, but you never know... Thanks.
B.Verlik wrote on 9/3/2004, 1:27 PM
Something, I just thought of, try using 'DVDdecrypter' to put the files on your hard drive and then use DVD Shrink for the rest. I think you can find it, if you don't have it, at DVDRhelp.com . It's free.
smurph wrote on 9/3/2004, 2:10 PM
Thanks Steve, but there is no need to use any software at all to transfer a VIDEO_TS folder to the hard drive from a burned dvd-r of course, just copy and paste. The individual who naively used DVD Shrink did so inadvertently, and I'm simply trying to gauge the potential differences between the two filesets.

If I can find a way to post this superposition of images from Bitrate viewer I will. Otherwise, thanks all for your help. If anyone has further thoughts, I'm all ears.
smurph wrote on 9/7/2004, 7:50 AM
JM,

You were absolutely correct about DVD Shrink not changing the bitrate. I did the initial comparison incorrectly. After redoing it, I noticed apparently identical q-levels and bitrates using bitrate viewer. The only reported difference was in the average bit rate, since during the transcode, the file size distribution changes, so each section will now show a change from the original. Not a big deal.

Thanks for your input,
Steve