DVD Times Explained - A Glossary
16:9 (or 16x9)
This is the aspect ratio of a widescreen television set. For every 16 units in width there are 9 units in height. 16x9 sometimes also indicates an Anamorphic transfer. It is roughly halfway between the European 1.66:1 and US 1.85:1 widescreen standards.
4:3 (or 4x3)
This is the aspect ratio of a standard television screen. It is also sometimes referred to as being in the ratio of 1.33:1. This is also the aspect ratio of virtually all films made before widescreen became an issue in the mid-1950s.
An unwanted effect that usually occurs on blinds, checkered clothes, garage doors or other symetrically arranged items - this is usually characterised by "waves" forming over the object rather than it remaining still. Though some DVD transfers have managed to improve this over video, it still occasionally occurs.
An Anamorphic transfer is a widescreen picture which is written in such a way that it uses a greater vertical resolution than a standard letterbox transfer. It can offer up to 33% more lines of picture information and this can result in a much sharper picture on television sets which can support it. The only drawback is the down-conversion from an Anamorphic picture onto a non-Anamorphic display source can sometimes introduce artifacts - although this depends on the hardware used.
There are many types of artifacts apparent on DVD. They range from MPEG2 Compression artifacts introduced by the encoding process to film artifacts which could include dust or scratches on the original print. The higher resolution on DVD also shows up weaknesses in the original print - a good print will always look fantastic on DVD, a poor print could look pretty bad. Artifacts can also be introduced by the downconversion of an Anamorphic source.
The Aspect Ratio is the ratio of width to height of the displayed picture. The most common on DVD are 2.35:1, 1.85:1, 1.78:1 (i.e. 16:9), 1.66:1 and 1.33:1 (4:3), though other aspect ratios are occasionally used. Most film fans prefer the picture to match that of the theatrical showing - as this is the ratio the director of the film intended you to view it. Some 1.33:1 transfers are what are known as open matte or full frame - this means that instead of using the Pan & Scan process, the picture has been opened up at the top and bottom to display more picture. For more details on different aspect ratios check out our Widescreen Unravelled feature.
The most common sound format on the DVD format. Dolby Digital supports anything up to 7 discrete channels of sound and up to two additional channels for low-frequency bass. Most commonly, Dolby Digital on DVD supports 5.1 channels (left, centre, right, surround left, surround right and sub) but the DVD format can handle any number of channels within the Dolby Digital specification. Dolby Digital is a compressed sound format and is stored at a variable bit rate. All DVDs MUST carry one form of Dolby Digital soundtrack to meet the DVD Forum specifications for the format.
An alternative to Dolby Digital, DTS (Digital Theatre System) is widely claimed to offer superior sound. DTS supports up to 7 discrete channels and up to two additional channels for low-frequency bass. Most commonly, DTS on DVD supports 5.1 channels (left, centre, right, surround left, surround right and sub) but the DVD format can handle any number of channels with in the DTS specification. DTS is a compressed sound format but generally undergoes less compression than Dolby Digital and is stored at a constant bit rate.
There is some debate as to what DVD stands for... Some people say it's Digital Video Disc while others say it's Digital Versatile Disc. The most accurate is the latter - DVD's can store more than just video, they are capable of holding data and audio as well. There are three main DVD playback formats - DVD-Video, DVD-Audio and DVD-ROM.
A single sided single layer disc. Can store up to 5GB of data.
A single sided dual layer disc. Can store up to 9GB of data. Sometimes refered to as RSDL (Reverse Spiral Dual Layer) although this is a specific kind of DVD-9 disc.
A double sided single layer disc. Can store up to 10GB of data - 5GB on each side.
A double sided single/double layer disc. One side is single layer, the other is dual layer or RSDL. Can store up to 14GB of data - 5GB on the single layer side, 9GB on the dual layer side. It is basically a DVD-9 and DVD-5 stuck back to back.
A double sided dual layer disc. Can store up to 18GB of data, both sides of the disc are dual layer and each side holds 9GB. Despite these huge advantages, they are rarely used because they are difficult to manufacture and unpopular with buyers, as they're easy to damage.
Touted as a possible replacement for CD (though this is looking increasingly unlikely), DVD-Audio offers by far the best sound quality that the format can currently store: six-channel uncompressed sound at a resolution up to 192kHz (compared with a CD's 44.1 or Dolby Digital's 48). Although the DVD-Audio format is different from DVD-Video, in practice virtually all DVD-Audio discs can play on DVD-Video players, albeit with inferior Dolby Digital or DTS sound. Although much of a DVD-Audio disc is taken up with the sound, the specification also allows for visual material - for instance, text, accompanying slideshows and a limited amount of video.
The most common type of DVD available. DVD-Video discs mainly store video images and are used for feature films, television series and very limited games.
DVD-ROM is a replacement for the CD-ROM found in virtually all modern computers. It's advantages are the greatly increased storage capacity and a higher playback speed. DVD-Video discs can also be played back via a DVD-ROM drive. There are a few DVD-ROM releases available and it is predicted that DVD-ROM will eventually supercede CD-ROM as the storage format of choice for computer users.
A Flipper is a DVD which needs to be flipped during the film. A disc with one version of the film on one side and another on the other is not regarded as a flipper. If a disc has to be flipped mid presentation then this is a flipper.
There are a number of different DVD configurations - Single Layer (DVD-5), Dual Layer (DVD-9 / RSDL), Double Sided Single Layer (DVD-10), Double Sided Single/Double Layer (DVD-14) and Double Sided Dual Layer (DVD-18). Each layer on a DVD contains information, at the end of the first layer the laser within the DVD player needs to refocus on the second layer. This can take anything from 1/10th of a second to 5 seconds depending on the disc and player.
This is another term for a widescreen picture. A letterbox transfer is usually one which is not Anamorphic. Any transfer with an aspect ratio greater than 4:3 and is not anamorphic is letterboxed. The name comes from the effect caused by the black bars displayed when outputting a widescreen picture to a television screen of a lower ratio.
All pictures encoded on a DVD are compressed using the MPEG2 algorithms. This compression can sometimes introduce artifacts - although newer discs suffer from these a lot less than early releases. MPEG compression involves only storing the changes between each scene and not the whole picture - this can dramatically reduce the amount of space required. However on large areas of colour, MPEG2 compression can have very strange effects where something in front the camera is constantly changing while the background only updates occasionally.
The television standard used in numerous countries including the USA, Canada and Japan. NTSC has a lower vertical resolution than PAL but has a greater number of frames per second (30fps) and a higher refresh rate (60Hz). The conversion from the theatrical 24fps to the NTSC 30fps involves a process where for every 5 frames displayed one is repeated - this introduces a 'feature' known as 3:2 Pulldown which can cause the picture to appear jumpy on horizontal pans. The lower vertical resolution makes the NTSC picture less clear than the PAL equivalent - scan lines are also much more visible on an NTSC picture.
The television standard in Europe and Australasia. PAL has a higher vertical resolution than NTSC but has fewer frames displayed per second (25fps) and a lower refresh rate (50Hz). Also the conversion from the theatrical 24fps to the PAL 25fps involves the speeding up the movie by 4% making all PAL DVD's run a number of minutes shorter than their NTSC counterparts. The higher resolution makes PAL transfers appear much sharper than the respective NTSC version.
Pan & Scan
This is the term applied to the conversion of a widescreen picture to fit a 4:3 screen. The picture takes up the full vertical height of the screen and sides are cropped. In order to pick up important information displayed to the left or right the view window is shifted or panned across the picture.
RSDL (Reverse Spiral Dual Layer) DVDs are the most common form of dual layer discs. Layer one of a RSDL disc is read from the inside to the outside, while layer two is read from the outside to the inside. This results in a minimal amount of time for transition between layers. Some DVD-9 and DVD-18 discs are not RSDL and when changin layers, the DVD laser must return to the inside track of the disc before commencing playback on the second layer. This results in a much lengthier pause between layers.
A PAL television picture is updated 50 times a second (NTSC is updated 60). On a standard display, the first 50th (60th) of a second contains lines 1,3,5,7 and so on, the second 50th (60th) the picture is made up of lines 2,4,6,8 etc. This makes up the 25 frames per second (60fps for NTSC). This is known as interlacing and can be seen quite clearly on DVD menu's where the screen flickers slightly - this flickering is more evident on PAL displays because of the lower refresh rate, it also stands out more on text. When you look closely at a television picture you can physically see the displayed lines - they are spaced very slightly. On a larger screen these lines are more apparent. Due to the nature of an NTSC display these gaps are more visible - there are fewer lines of picture information in the same amount of space taken up by the equivalent PAL display. These are the scan lines.
The vertical resolution refers to the number of lines displayed on the screen - in the picture area. The higher the number of lines displayed, the better the picture. Anamorphic transfers always display more lines than non-Anamorphic transfers on a screen which supports an Anamorphic display. The table below details the number of lines of resolution available from different picture sources.
|Data gathered by Charlie Pearce|
Any picture with an aspect ratio greater than 1.33:1 or 4:3 is considered as being widescreen. Widescreen is also sometimes refered to as being a letterbox picture - although this can sometimes be inaccurate.
This is the name given to a picture which has bars at the sides instead (or as well as) bars at the top and bottom. 4:3 pictures are occasionally displayed windowboxed on widescreen televisions.