I recently received an email from someone with some questions about DVD video discs, their files and structure and the relative safety of different methods of DVD recovery or repair.
My reply kind of went on a bit as I am inclined to do so I thought I had better post it here so I don’t have to cover it again… I’m lazy like that.
The Basics of DVDs and DVD Video File Structure
So to begin with let’s clarify our terms here because this is one of the basic sources of confusion.
When we say “DVD” we can sometimes mean a DVD disc or we can sometimes mean a DVD disc that has video on it that we can use to watch a movie of some kind.
So let’s start with a DVD that has simply been used to store data just like a data CD or data being held on a computer hard drive.
This is just a set of folders and files in those folders.
There is nothing nothing special on these discs except for perhaps a couple of hidden files which are there to tell the DVD reader that it is looking at a data DVD.
It communicates to the reader that the information on the DVD will be in the form of folders and files and where physically on the disc the start of that data occurs.
On a video DVD things get a little more complex.
Again it’s just files and folders that tell the DVD reader what is on the disc, where it is and how to deal with it.
If you place a video DVD into the reader on a computer and select “Open” instead of “Play” you can see the file structure for yourself.
You will first see two folders.
One is called VIDEO_TS and the other is called AUDIO_TS.
You and I do not need to know why they are called that, why they always are named using capital letters or even why they always use the underscore then TS.
Bottom line is that they do!
Inside the AUDIO_TS folder you will usually find nothing.
I have never come across a DVD that ever had anything in there.
From what I understand, in the early days of DVD there was the intention to have some kind of audio information in there but that never panned out but to this day it still gets created.
I guess we can just put that one down to one of life’s mysteries!
The VIDEO_TS folder is the one that has everything you need to be concerned with in it.
Inside that folder you will find three types of files.
1. The .IFO file.
It is called that because it comes from the word “information.” InFOrmation file, see what they did there?
The .IFO file contains… you guessed it… information!
The information it has concerns all the data ABOUT the video on the DVD, Start points, end points, chapter points, menus and a bunch of other stuff.
The DVD reader uses the .IFO file to navigate around the DVD itself in order to load the video, play it, rewind, show the menus etc. In other words it provides all the functionality you get with a DVD.
2. The .BUP file.
This one comes from the word “backup.” Back UP.
This file is just a backup copy of the .IFO file and is only there in case the .IFO file was not written correctly or for some reason the DVD reader cannot access it.
If that happens all software that deals with video DVDs is programmed to fall back on the .bup file if the .ifo file is unreachable.
3. The .VOB file.
This one gets its name from Video OBject file = .VOB.
The .VOB file is a special type of file called a “container” or “wrapper” file.
It is used to take one type of file and “wrap” it in such a way that extra information can be added to the file being wrapped.
In the case of DVD video the file being wrapped up is the underlying MPEG2 video files that have been added to the DVD.
MPEG2 files are purely video files, nothing else.
The purpose of the .VOB wrapper is to add marker points or little signposts to parts of the MPEG2.
Imagine the MPEG2 file as a whiteboard that has a bunch of information on it.
Now imagine that you want to highlight or mark certain parts of that information with post-it stickers for easy reference.
Unfortunately your whiteboard has been covered with oil so there is no way to add the post-it notes!
You can wrap the entire whiteboard in cling wrap so you can easily see the data on the whiteboard and can now stick your post-it notes to the cling wrap.
The MPEG2 files are the whiteboard and the .VOB file is the cling wrap.
By doing this the .IFO file and the .VOB file have corresponding information that allows the DVD player to know what is going on and how to execute instructions such as Play, Stop, Pause, Go to Chapter, Fast Forward, Rewind, Go Back to some point etc.
The other function of the relationship between the .IFO file and the .VOB file is when you are recording video to a disc on a “stop and start” basis.
You start recording then stop and later come back and record something else and stop and on and on.
This results in a bunch of smaller MPEG2 files recorded during each recording session.
For a DVD reader to be hopping around trying to find all the bits and pieces of video files is asking a bit much so, the .VOB file pulls them all together into what appears to be one big MPEG2 file.
Generally on a video DVD you will find two .VOB files.
One will be rather large and that will be the actual videos on the disc.
The other will be much smaller and that one will be the menus you see when you play a disc. Yes, the menus themselves are little MPEG2 video files that play when you insert a disc.
As mentioned before when a video is being recorded to a DVD, an MPEG2 file is being created as you going along.
Once the disc is full or you have recorded everything you need to, the disc needs to be finished off in such a way as to be readable by DVD players.
For a data disc of any kind this means to “close” the disc.
Closing simply involves writing information to the disc to let any disc reader know what’s on the disc and where it is.
Finalization closes the disc in the same way but does a lot more than that as well.
The program finalizing the disc locates the physical address of everything on the disc and adds that information to the .IFO file, it creates the .VOB file around all the relevant MPEG2 files, creates the .BUP file and generally completes all the things that need to be done to result in a readable and playable video DVD with a menu structure.
So an unfinalized disc usually has all the information needed to complete the finalization process.
However the program or software being used to execute the finalization may have organized that information in a way that makes it impossible for another program to understand.
The writing program may have also stored information regarding the disc in it’s own internal memory and without that information again, another program may find it impossible to finalize the disc.
Obviously by far the best way to deal with an unfinalized DVD is to get the original software or recording device to finalize it!
Just as obvious is the fact if you are reading this, that’s probably not a possibility!
So, here’s the deal.
The simplest approach is to get another software program like Ahead Nero to finalize the disc.
The reason I mention Nero is is because it is easily the most compatible.
It has the most number of alternative strategies written into it for finalizing DVDs created by other programs and devices.
This doesn’t mean that it can finalize all discs you throw at it it, it just means that of all the programs out there this one is your best shot at handling this situation quickly and easily.
The question is, “Is there any inherent danger in this process?”
In other words, can video files be lost in any way beyond recovery and the answer to that is no.
When you load Nero and then insert the disc and instruct Nero to try to finalize the disc the process itself requires that ALL data must be present and correct before Nero will try to finalize.
If ANYTHING is missing that Nero needs to finalize the disc then it will simply give you a message that it cannot do it.
It is a yes or no, black or white situation and if it says yes, you can safely proceed.
If Nero cannot complete the task then it is important to understand that finalization of the disc is no longer a possibility and that the action of recovery has now changed completely.
You are now not trying to finish off the disc you have.
You are now trying to extract the underlying MPEG2 video files off the disc and onto a computer hard drive.
If you can do that then you can use those MPEG2s to create another disc using video editing software or DVD authoring software to do so but, that is an entirely different process.
What we are solely discussing here is the recovery of data from unfinalized discs.
It is at this point that you can use other functions of Nero or switch to Isobuster to extract the MPEG2 files as described on these pages of the website.
- A Step by Step Guide to DVD CD or Game Disc Repair
- Data Recovery for all Optical Discs Such as DVDs CDs and Game Discs
Further Reading: DVD on Wikipedia