DVD Terms Explained

This thread is intended to give explanations and definitions for some DVD terms you may run into during the authoring process. I'll be adding more terms as time permits. Feel free to post any questions, comments, or corrections in this thread: http://forums.afterdawn.com/thread_view.cfm/243225

 

1. VOB, IFO, & BUP

2. VM Commands

 

1. VOB, IFO, & BUP

VOB (Video OBject) files are where the actual content you see and hear is stored.

IFO (InFOrmation) files are where the instructions (VM commands) that tell a DVD player what to do are stored.

BUP (BackUP) files are exact copies of IFO files. If a player can't read a particular IFO it will use the corresponding BUP file instead.

 

2. VM Commands

In order to make DVDs capable of containing a variety of different playback options and interactive features it was necessary to create a sort of scripting language for the DVD specifications. To further complicate matters the standard had to be written without a specific hardware platform in mind. In order to create a standard set of commands it was necessary to define a virtual machine (VM). If you're familiar with the concept of a virtual machine in computing (ie Java or VMWare) this is basically the same thing. The virtual machine makes it possible for every DVD player (hardware or software) to react identically to commands.

For this reason the commands used on a DVD are sometimes referred to as VM commands. If you've ever done any type of assembly programming they will probably look very familiar to you. The DVD-Video VM has 8 bit registers that it can set, compare, and perform basic math on. There are also simple commands to playback specific video, audio, and subpicture streams.