The World of DVD

Current CD-ROM discs are able to storage a maximum of 640MB. DVD, the successor to CD-ROM, discs are able to store up to 4.7GB of information! And that's just the beginning. Using dual layer technology, the storage capacity will double to 9.4GB per disc. In addition, information may be encoded on both side of the DVD disc, giving us an incredible 18GB per DVD in the near future.

So what can we do with 4.7GB of information? We can put a full-length movie (2+ hours) encoded in MPEG2 format with Dobly Digital 5:1 (or AC-3) on a single 4.7GB DVD disc today with room to spare! Because of the extra free space, most DVD titles comes with different language tracks: English, Spanish, French, etc. A little known fact about DVD is that it really doesn't stand for anything, but people have associated DVD as Digital Video Disc

MPEG2 is a processor intensive compression / decompression scheme. The visual quality of a typical DVD movie is much sharper and better than super VHS or even a laser disc. Unfortunately, quality comes with a price: an Intel Pentium II/333 or faster processor is required in order to perform software MPEG2 decoding. Because of this, most PC DVD kits rely on a dedicated MPEG2 decoder PCI card. Due to current technology, this is an inexpensive solution since it frees up processor for other use.

In addition to the high quality visual aspect of DVD, it also incorporates Dobly Digital 5:1 or AC-3. This is an audio encoding scheme developed by Dobly Labs. Scroll down for more.

05/11/1998

MPEG2 Decoding

MPEG2 Successive Frames - 3K The principle of MPEG2 is relatively simple. Figure 1 on the right shows how each frame of a movie is stored using MPEG2.

Instead of storing each frame of a movie, MPEG2 stores the transitional changes between each frame. It starts with a key frame. Every frames after the key frame are the changes between each frame. Periodically, a new key frame will be generated; in case there's a bad spot on the DVD or the DVD drive skips a track during playback.

To decode the changes between each frame requires a great deal of processor time. Only a system with an AGP video card equipped a Pentium II/333MHz or faster processor is capable of performing the decoding without losing any frames. Alternatively, a dedicated MPEG2 decoder card may be added to the system.

05/11/1998

Dobly Digital 5:1 Layout

AC-3 Layout - 4K Dobly Digital 5:1 (also known as AC-3) is an audio encoding process that gives the listener the illusion of total surround sound. AC-3 consists of five speakers and one bass unit (hence the name 5:1). Referring to figure 1 (not drawn to scale) on the right, the listener is surrounded by two front speakers and two rear speakers, both pair of speakers with full stereo capabilities. The center speaker is mainly used for dialogue between actors and actresses.

Because both the front and rear speakers are stereo, AC-3 is able to simulate the movement of objects (such as a shot fired) from back to front and vice versa.

For example, sound may be encoded so that the sound begins from the rear right speaker and travel to the front left speaker.