DVD to DVD copying

Now that prices of DVD burners and recordable DVD media are coming down rapidly, many people will get interested to learn how to copy an existing DVD-Movie to a blank DVD. This article will give some basics and an overview of available copy methods.

Issues related to DVD copying
- Protection Mechanisms
- Disc size
The DVD data structure
- The audio_ts directory
- The video_ts directory
DVD to DVD copy methods
- Simple copying
- The Rip and Re-encode method
- The Editing method

1. Issues related to DVD copying

There are basically two types of issues making DVD to DVD copying more complex than CD to CD copying.

The mechanism to prevent digital copying is a technology called Content Scrambling System (CSS). The streams on the DVD are scrambled using one or more CSS keys. Since the keys are on the DVD itself it is not a very sophisticated mechanism. Quite soon after the introduction, it was already cracked by a young Swedish boy who developed an algorithm to scan the DVD and find the applied keys. Rippers like Smartripper and DVDdecryptor make use of such an algorithm.

In order to prevent that DVD's are easily spread from one part of the world to another, region protection was developed. This works by putting a code on the DVD's and in the hardware of DVD players. Result is that DVD's with a code for a certain region can only be played on players designed for this region. More and more DVD players on the market are region-free, making this mechanism quite useless. Furthermore, on the Internet you can find many pieces of software that you can use to change the firmware of players to make them region-free. Also, the region code on a DVD can be easily found and altered or removed during copying.

The major obstacle to copy DVD to a recordable DVD today is the disc size. Most commercial DVD's are dual layered and contain too much data for a recordable DVD. Recordable DVD media are only single layered and can contain only 4.7Gbyte of data. There are three ways to deal with this problem:

Removing data
While copying, you can leave out some data which you may not need. Types of data that you may want to consider are for example extra's like trailers and/or certain language tracks and subtitles.
Changing the bitrate of the stream
Since streams on a DVD do not have to comply with a certain fixed bitrate you can re-encode the stream to make the filesize smaller.
Distributing the data over two discs.

2. The DVD data structure.

When you browse a DVD on your computer, you will see that it always contains two directories. Video_ts and Audio_ts.

The audio_ts directories was originally meant to contain all of the audio data, but in practice it is almost always empty and the audio data is multiplexed in the streams in the video_ts directory. Nevertheless, in order to work properly on most DVD players it must be present.

When you browse this directory you will note three types of files.

These files with the extension .VOB contain all the streaming data that is sent to your screen or speakers (menus, video, audio and subtitles). Often you will find a file called Video_ts.vob, which contains some streams which are played at startup, like a copyright notice, a trailer or maybe even the top level menu. Further you will a whole bunch of files with the named Vts_xx_y.VOB where xx can be any number from 01 through 99 and y can be any number from 0 through 9. Usually xx represents a title on the DVD. Since the maximum filesize on a DVD is 1 Gbyte the VOBs are further divided in separate files using the y value.
If your DVD playing software on your computer supports playing files, you can play the VOB files independent from any other files on the DVD. If you do so you will see either a menu or a (part of) a movie, but you will not be able to interact like changing language, select subtitles or select a menu item.
You can also analyze in more detail which streams are inside the VOB files. A neat program that you can use so is VOBrator. A typical screenshot of a .VOB file opened in VOBrator is shown below.

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