DVDs can be duplicated by copying or burning them. It may be a good idea to copy your DVD Movie collection in case of damage or theft. In order to save your DVD collection you must first know how to copy a DVD movie.
From wikihow, it said you can copy a DVD with following ways:
1. Copying with FreeDVD
2. Copying with DVD Shrink
3. Copying to a Disk
Source: How to Copy a DVD Movie
If you are a Mac users, you can try some applications, such as:
1. HandBrake
2. Cisdem VideoConverter