DVD glossary

ADPCM

Adaptive Differential Pulse Code Modulation compression technique that encodes only the difference between sequential samples.

ATime

Address information contained in a block identifying a unique block location for receiving systems in absolute elapsed time measured in minutes, seconds, and blocks referenced to the beginning of the program area.

ATIP

Absolute Time In Pregroove similar to ATime but used by a writer for unrecorded disc addressing.

Astigmatism

Distorted spot resulting from imperfect focus caused by a defect of an optical system.

AC-3 (now Dolby Digital)
Dolby Digital Surround Sound System. A digitally compressed audio format that can offer up to 6 separate digital audio channels. AC-3 is used for DVD-Video titles in the NTSC format. Standard digital data such as those used on CD would take up too much data on a DVD-Video, hence the use of a compressed audio format.

Aberration
A variation in the focus of a laser beam that causes the laser beam to become diffused. The aberrations cause focusing errors in the laser pick-up and cause the DVD to be miss-read.

Academy
Name for 1.33:1 aspect ratio film

AES
Abbreviation for Audio Engineering Society.

AES/EBU Interface
The standard for digital audio signal transmission for professional use developed by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU). The AES/EBU systems use 110-ohm balanced XLR cables. The consumer version of the digital audio transmission standard is called S/PDIF.

Amplifier
A device that provides power to a signal, ultimately resulting in powering loudspeakers in the case of home theater.

Anamorphic
A wide-screen process of recording images, in video and film, so that each frame is horizontally compressed "squeezed" on a videodisc or strip of film. During playback, the image is expanded, restoring to its original size. Anamorphic film is best viewed in the wide-screen format. Brand marks include Cinemascope and Panavision.
This type of display format is optimized for playback on a TV with 16:9 aspect ratio. When wide-screen (letterboxed) movies are stored on VHS, Laserdisc, or non-anamorphic DVDs the horizontal scan lines that make up the black bars top and bottom are also stored. This is a waste of resolution because lines that could be used for the picture are being used to store the black bars. With anamorphic DVDs the widescreen picture is "squashed" to fit into a whole frame without black bars. If this were viewed without first "un-squashing", the picture would be out of proportion e.g. the actors would look tall and thin. The DVD player must expand the picture to get it back to the original proportions and then either send this picture to a widescreen 16:9 TV or add black lines top and bottom for a standard 4:3 TV. Basically, any DVD that is "enhanced for widescreen TVs" or is "anamorphic" will give better picture quality on widescreen TVs where the picture would otherwise have to be "zoomed" to fit the 16:9 frame.

Artifact
An anomaly that occurs on a video image as a result of a problem in the film to video transfer, or problem with playback. A common artifact on DVD is pixelation, where individual pixels or groups of pixels produce an unnatural, "blocky" image. Other examples include image flicker, color shift, loss of resolution or changes in aspect ratio. On DVD, artifacts are usually a symptom of poor mastering, poor playback equipment, or improper adjustment of your television monitor. Make sure to calibrate your picture using a test disc like Video Essentials if you feel you are seeing artifacts.

Aspect Ratio
The width-to-height ratio of a television screen, letterboxed image on that screen, or motion-picture theater screen. Typical TV sets have a 1.33:1(4:3) ratio, while wide-screen versions have a 1.77:1 (16:9) ratio. Common aspect ratios for film and video are 1.33:1 (Academy), 1.78:1 (widescreen TV and HDTV), and 2.35:1 (Cinemascope).
Video can be stored on a DVD in 4:3 or 16:9 format. DVD players can output video in four different ways:
- full frame (4:3 video for 4:3 display)
- letterbox (16:9 video for 4:3 display)
- pan & scan (16:9 video for 4:3 display)
- wide screen (16:9 video for 16:9 display)
Letter box is when you have the black bars at the top and the bottom of your TV, Pan and scan is where the picture has been modified to fit your TV, i.e. chopping off the sides of the frame.

Audio Frequency
Frequencies within the range of human hearing (20 Hz to 20kHz).

Audio Streams
DVD has the ability to hold a maximum of eight audio streams on a single disc. This allows DVDs to have up to eight different language tracks for multiple languages and/or director's commentary.

Authoring
In the case of DVD, it is the process of creating video (MPEG-2) from film.

Average Bit Rate
Average volume of data (in a variable bit rate DVD system) measured over time. DVD uses variable bit rates for optimized storage capacity on a disc.