Overview

Stucture

Specs

Q & A

Sources

Structure

    The file structure on a DVD is a Micro UDF, a universal disk format initially combined with ISO 9660.  The Micro UDF file format extends  what is currently possible with ISO 9660

    The CCIR-601 is the digital video standard that specifies a video rate of 167 megabits per second.  At this bit rate, the 4.7 gigabyte capacity of a standard DVD could only store roughly 4 minutes of digital video! Thus, some form of data compression is required.

    DVD takes advantage of a sophisticated compression technology called MPEG2.  It's a set of flexible compression standards, the second to emerge from the Moving Picture Experts Group (MPEG). 

    MPEG2 works by analyzing the video picture for repetition, called redundancy.  In fact, over 97% of the digital data that represent a video signal is redundant, and can be compressed without visibly harming the picture quality.  By eliminating redundancy, MPEG2 achieves superb pictures at far lower bit rates.

    As implemented for DVD, MPEG2 encoding is a two-stage process, where the signal is first evaluated for complexity. Then, higher bit rates are assigned to complex pictures and lower bit rates to simple pictures, using an "adaptive," variable bit-rate process. The DVD format uses 4:2:0 component digital video compressed to bit rates with a range of up to 10 megabits per second.  Although the "average" bit rate for digital video is often quoted as 3.5 megabits per second, the actual figure will vary according to movie length, picture complexity and the number of audio channels required.

CD VERSUS DVD PIT SIZE COMPARISON

    Compared to CD, DVD uses smaller pits and a more closely spaced track. The result is a significant increase in data density. The higher Numerical Aperture (NA) lens of DVD helps the laser focus on the smaller pits.

The DVD format provides multiple configurations of data layers.  Each configuration providing additional data capacity. The configurations are:

The basic configuration of Single Side, Single Layer is 4.7 GB of data capacity.  This 4.7 GB is "7 times" the data capacity of today’s music CDs and CD-ROMs.

The Single Side, Dual Layer      
configuration provides a total of 8.5 GB on one side using an additional 3.8 GB on the second layer. This is more than "13 times" the capacity of today’s music CDs and CD-ROMs.

The Double Side, Single Layer
configuration provides a total of 9.4 GB (4.7 on each side). This configuration provides a little more capacity. However, because half of the data is on the second side, it requires either flipping the disc or having a DVD Player capable of two-sided playback.