If you intend on ripping DVD's it helps if we have some
idea of what we are actually ripping. When you rip a whole DVD to your
hard drive you will see something like the picture below:
I guess you are wondering what all these files are there
for, huh. Well to summarize:
Video Transport Stream (VOB = Video Objects)
Navigational information (IFO = Information)
Navigational info backup (BUP = BackUP)
Secondary navigational information
Secondary Navigational information backup
For the most part the only files we are concerned about are the IFO
and VOB files. The rest are needed more by a DVD player for error
correction and seeking requirements.
When I refer to a "title" in my articles I mean a feature of
a DVD. For example, DVD's usually contain the main movie. That is the
1st "title". Then they will have the main trailer, 2nd "title".
Then they may also have the short trailer 3rd "title". Then
they will have the specials (if any) such as the making of the movie 4th
"title". Finally, they will have a small movie clip used for
the options and selection menus 5th title. Even still picture menus are
made into a slideshow movie so there is rarely any additional files. If
you do find additional files they are probably meant to be installed on
a PC, like in the Matrix DVD which has an interactive presentation on
DVD Vob files contain lots of things bundled together. Imagine each Vob
as a box containing various items. The two most important items inside
it are the Mpeg-2 video and the Ac3 (or Mp2 / PCM) audio streams. A Vob
file can contain many audio tracks at the same time. One can be English,
another French, German etc., then you can have alternate music scores
and director comments and so on all as separate tracks. A Vob file can
also contain subtitles which are usually in the form of transparent pictures
that are displayed over the top of the played DVD like a slideshow.
If you play a Vob file back it will usually play everything together
i.e. you will hear both the French, German, English and the Directors
comments all going at once! This is because they are Multiplexed as one
single file. This basically means every file is chopped up into thin slices
and stacked together like a pack of cards.
Vob files may also contain repeated sequences. It may have one second
of one scene in English, then one second of the same scene but
in German, and then French and so on. If you were to play it back you
wouldn't be able to watch it as a whole movie. This is a big waste of
space, but on small movies and cartoons it is still done. Other movies
have different playbacks for people of different ages. This means the
whole movie is all there but extra scenes are spliced into the movie for
people who are older. This method is also popular for cut movies that
give the option to play both the cut and uncut versions. In this case
you will get both scenes played one after each other. Then we have multiangle
movies where you will get the movie played for so long from one camera
view, and then the same scene played again from another angle. This is
done so the viewer can choose which view to watch as they watch the movie.
It is obvious from the above picture that the largest VOB files on the
DVD will be the main movie, the next largest files will be the special
features, the next largest files will be the trailers and finally the
smallest files the menus. But almost all DVD's will have VOB files that
are split into 1 GB files each. So a single movie will usually be built
of 2-7 or more 1 GB VOBs. The trailers will just be a single VOB or sometimes
just stuck on the end of the movie. And any special features may be built
out of one or more Vobs. These Vobs are not separate chapters but are
all part of a single title. This can be likened to a book, you will have
many pages to a book but only one book. In the same way there are many
Vobs to a DVD movie, but there is no pause between them they are played,
they are read as one single file.
Every movie or title on your DVD has its own special name. For example,
the main movie in the picture above is called:
All Vob files that are part of that title will be numbered in order like
So you will know that Vts_02_xx is not part of the same title or feature
As you can see from the previous descriptions of the Vob files, it would
be impossible to play most Vob files back in a DVD player without some
sort of guidance. If you did, you may get many languages playing at once.
All subtitles appearing on screen and repeated scenes all over the place.
Then when it reached the end of the first 1 GB Vob file it would stop
because it wouldn't know what to play next!
Luckily few DVD's are quite this complex. But nevertheless, they do need
information on how they should be played back. And this information is
contained in the IFO files. Each IFO file contains a "play list"
which tells the DVD player exactly what scenes to show, what subtitles
to display and what audio track to use for each selection we make.
Again, each IFO file has is own special name which is always the same
as that of the DVD. So going back to our example: the main movie on this
DVD is called:
So the IFO file that describes how to play that movie is also called:
If we wanted Flask Mpeg to read this movie like a DVD player would we
would open it in DVD mode and choose:
Then Flask would know that it is supposed to play back the Vobs
If you opened:
You would probably end up with the special features of the DVD and opening:
Would give you a movie trailer
Well, that's about all you need to know about the structure of a DVD.
Hopefully this will help you with your decoding of them to DivX.
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prohibited. (C) NICKY PAGE 2000