Welcome to our A-Z of DVD, a glossary of common terms found in the world of DVD. If you have any suggestions, amendments or additions please email them to Ed@dvd-recordable.net

5.1
The five indicates the number of sound channels available - in this case there would be front left and right, rear left and right and centre. The number after the dot indicates sub-woofer support.

Artifacts
Flaws in video caused during conversion to DVD, often by trying to compress too much information on to the disc.

Authentication
Before a movie can be played the player and the disc have to establish a secured communication line on which they can transfer the actual movie. Before they can establish that line they need to make sure that the right 'person' is on the other side - this is done via several key exchanges, verifications, etc.

AC3
Initially known as Audio Coding 3 AC3 is a synonym for Dolby Digital these days. Dolby Digital is an advanced audio compression technology allowing to encode up to 6 separate channels at bitrates up to 448kbit/s. For more information please check out the Dolby website.

ASF
Advanced Streaming Format. Microsoft's Windows streaming media format.

Aspect Ratio
The ratio of width to height. Widescreen is 16:9, while the standard television aspect ratio is expressed 4:3.

AVI
Audio Video Interleave. This is the video format that is most commonly used on Windows PC's. AVI defines how the video and audio are attached to each other, without specifying a codec.

BUP files
These are backups of the IFO files, Useful if the IFO files get corrupted.

Chapter
Just like in a book, DVDs are split into chapters for easy referral and access.

Codec
COder/DECoder: This is a piece of software that allows you to encode something, usually audio or video, to a specific format and can decode media encoded in this specific format again. Popular Codecs are MPEG1, MPEG2, MPEG-4, Indeo and DivX. AVI and ASF, are not codecs but rather a format that can be encoded using different codecs.

CSS encryption
Content Scrambling System. This is the encryption method used in DVDs. It is a copy protection scheme designed to prevent unauthorized copying of DVD movies (although many argue that CSS was also designed to control where DVD movies can be played since without a CSS license you essentially have to crack the encryption just to play a DVD movie). The encryption allows files to be copied off a DVD, but the resulting files will contain data that will be useless. However, not all files on the DVD are encrypted though and different files may use a different decryption key.

Demultiplexing
This is the opposite of multiplexing where a combined audio/video stream will be separated into the number of streams it consists of (a video stream, at least one audio stream and a navigational stream). Every .VOB encoder demultiplexes the .VOB files before encoding (FlaskMpeg, mpeg2avi, dvd2mpg, ReMpeg2) and every DVD player does the same (audio and video are being treated by different circuits, or decoded by different filters on a PC).

Descrambling
Descrambling means reversing the scrambling process, making movies that are scrambled with CSS (content scrambling system) playable again. If you try to copy a movie to your hard disk without descrambling it you will receive a garbled picture because it is still scrambled. Common CSS descramblers either use a pool of known descrambling keys (DeCSS or DODSrip) or try to derive the key by a cryptographic attack (VobDec).

DivX
This is not to be confused with the now obsolete DIVX (DIgital Video eXpress) system introduced by Circuit City 1998. DivX is the name of the hacked Microsoft Mpeg4 codecs (Windows Media Video V3). Those codecs were developed by Microsoft for use in it's proprietary Windows Media architecture and initially supported encoding AVIs and ASFs but all non-beta versions included an AVI lock, making it impossible to use them to encode to the AVI format - and only a few tools support ASF today. What the makers of DivX did was remove the AVI lock making it possible to encode to AVI again, and changed the name to DivX video in order to prevent confusion of codecs, since it's possible to have both the unhacked and hacked codecs on the same computer if you use the Windows Media Encoder. The image quality on DivX can range from below VHS up to DVD depending on the bitrate and resolution you choose. You can make DivX CDs that are almost identical to DVD if you use the right software including such features as multi-language, subtitles, menus, etc. A current disadvantage is that there is no stand-alone player and DivX can only be played on Windows (and Macs if you convert it to ASF).

Dolby Digital
This proprietary technology is used to decode high-quality sounds from the DVD. For more information please check out the Dolby website.

DRC
Dynamic Range Compression. AC3 Tracks contain a much larger dynamic range that most audio equipment can handle, therefore most standalone and software DVD players will compress the dynamic range somewhat, according to the actual dynamic range. In layman terms the volume will be augmented dymanically, e.g. explosions won't become louder or only a bit louder, whereas in normal dialogues the volume will be augmented quite a bit. Since your player will do the same this is the way to go to have augmented volume.

Dual-Layer
A dual-layer disc has two layers of data, one of them semi-transparent so that the laser can focus through it and read the second layer. Since both layers are read from the same side, a dual-layer disc can hold almost twice as much as a single-layer disc, typically 4 hours of video. more info.

DVD-R and DVD-RW
These 2 disc types were created by the DVD Forum. By contrast to the write-once DVD-R types, the DVD-RW is fully re-writable or eraseable up to 1,000 times. The 'minus' format is the most popular format for most Windows users, and is almost universally accepted by Mac users as their standard DVD recordable format. Read our FAQ for more info comparing DVD formats.

DVD+R and DVD+RW
These two types were created and are backed by the DVD+RW Alliance. A few companies who back the DVD Forum (above) are also active in the DVD+RW Alliance, but the two standards are not compatible. The oldest "plus type" DVD is the DVD+RW. It, like DVD-RW, is a rewriteable 4.7 GB DVD kind of disc. DVD+RW, does have a couple of technical advantages -- (1) lossless linking (which enables some editing after recording without a full erasure that DVD-RW requires), (2) up to 2.4X recording speeds on some burners, and (3) a special drag-and-drop file support on the desktop (otherwise known as DVD+MRW). Unfortunately, the DVD+R disc type does NOT even begin to compare with DVD-R as far as DVD playback compatibility. However, the actual level of DVD workability on players of DVD+RW is claimed to be about equal to DVD-RW. Of course, even so, neither the DVD+R nor the older DVD+RW discs are as popular as DVD-R and DVD-RW are. Read our FAQ for more info comparing DVD formats.

DVD-RAM
DVD-RAM is used for data backups and storage, and for editing of video or audio content prior to the production of a final distribution DVD. The DVD-RAM disc type is made to act a lot like a hard drive, where the disc can be formatted for HFS+ Macintosh or Windows type computers, and so on. It can handle 100,000 or more erasures, and should last for many years. Of course it is not playable on many DVD players. Type 2.0 DVD-RAM discs can be removed from their cases to enable playback on the few players in which they are compatible. The newer DVD-RAM drives can handle any sized such disc, including 2.6, 5.2, 4.7 or 9.4 GB discs. Read our FAQ for more info comparing DVD formats.

Easter Eggs
These are hidden features that many DVDs now contain and can usually be accessed via a hidden icon on a menu.

FourCC
FourCC stands for four character code and is a code that uniquely identifies a video data stream format. A movie player will look up the FourCC code then look for the codec associated to the FourCC code in order to play a certain video stream. A few examples: DIV3 = DivX Low-Motion, DIV4 = DivX Fast-Motion, DIVX = DivX4.

Frame
The basic source of a movie. One frame represents one image. A movie usually runs at 24 frames per seconds, so it has 24 different images per second. Imagine 24 images with a bird on it, in the first image it's on the left, then it gradually movies somewhat to the right. On the 24th frame the bird is on the right end of the image. Imagine these 24 images being played in sequence fast enough and it looks like a bird would fly from left to right to the human eye.

Frame Rate
Number of frames (see above) per second displayed in motion.

I and P Frames
Frame describing only the differences to the frame before (this is less than accurate but I think you'll get the picture that way). Say we have a keyframe with a bird before a cloudy sky. Then we can use I frames which say something like this : move the bird an inch to the left and one inch to the bottom.

IFO Files
These files contain the formatting information of the .VOB files, which tell the DVD player exactly how the DVD should be played (i.e., which subtitles to use, which languages, etc.). If you Rip the DVD without .IFO files, then the .VOB files may not play correctly, or may not even play at all.

Layer
This is where all the information appearing on your screen is physically stored on the DVD disc. DVDs can be double sided (two layers) though reliability is questionable with cheaper DVD players. See also 'dual-layer' above.

Letterbox
The use of upper and lower black mattes to keep films in their original aspect ratio, ie a film in letterbox format will have black margins at the top and bottom of the screen to keep the viewable film to the correct rectangular shape.

Macrovision Copy Protection
This is copy protection to prevent DVDs from being recorded by VCRs. Macrovision copy protection is encoded onto .VOB files. Some Rippers offer you the ability to rip out Macrovision protection during normal Ripping. Once Ripped this way, the files will play in any DVD player, and will not have Macrovision or region protection problems. Read ouor FAQ on Copy Protection for more info.

Merging
Some Rippers allow you to "merge" the .VOB files during Ripping. We do not recommend doing this as merging .VOB files will most likely damage their file structures.

MiniDVD
This is basically a DVD on a CD. It can contain bitrates up to 10mbit/s (audio and video combined). The video is MPEG2 and the quality can be up to an actual DVD level if you accept the limited playtime of a CD. You can create DVD-like menus as well. The drawback is that miniDVDs will only play on PCs.

MPEG
Motion Picture Expert Group. This is the definitive resource for video formats in general. This group defines standards in digital video, among it the MPEG1 standard (used in Video CDs), the MPEG2 standard (used on DVDs and SVCDs), the MPEG4 standard and several audio standards - among them MP3 and AAC.

Moire
The circular lines or flickering that occurs when television screens are filmed.

Multipass encoding
Before you read on: Currently true multipass encoding is available only for WM8 and MPEG-2 (SVCD & miniDVD). M4C is not true multipass encoding (and read the M4C guide to find out what it is and how it works). An encoder that supports multipass will in a first pass analyze the video stream to be encoded and write down a log about everything it encounters. Let's assume that we have a short clip which starts out in a dialog scene where we have few cuts and the camera stays static. Then it leads over to a karate fight with lots of fast cuts and a lot of action (people flying thru the air, kicking, punching, etc). In regular CBR encoding every second gets more or less the same bitrate (it's hard to stay 100% CBR but that's a detail) whereas in multipass VBR mode the encoder will use the bitrate according to its knowledge about the video stream, that is the dialog part gets of the available bitrate and the fighting part gets more bitrate. The more passes the more refined will the bitrate distribution be. In single pass VBR the encoder has to base his decisions on where to use how much bitrate solely on the knowledge of the stuff it previously has encoded.

Multiplexing
Usually video and audio are encoded separately. You then have to join both of them to make a movie that you can play. During multiplexing the audio and video track are combined to one audio/video stream. The audio and video stream will be woven together and navigational information will be added so that the player can have fast forward/backward and still retain synch audio/video.

Normalizing
Normalizing consists of finding the volume peak of a soundtrack, then increase the rest of the soundtrack to the same level. This is usually done at WAV level, that is all variables are integers so the precision is not as good as in DRC. Hence DRC is to be preferred over Normalizing.

Parental Lock
Allows users to block certain content

PGC
PGC stands for ProGram Chain. It is a term often used in DVD authoring it's basically one concurrent playback item. For instance the main movie has its own PGC, each trailer on a DVD usually has its own PGC. The studio logo that comes up when you enter the disc has its own PGC, etc. Both SmartRipper in Movie mode and DVD Decrypter in IFO mode will show you all PGCs a DVD has.

Pixel
When a display is measured in pixels then this is the number of individual 'dots' of colour on the screen.

RSDL:
Reverse Spiral Dual Layer. Format used to allow scanning of two layers of a DVD disc with a minimal delay between layers. See 'dual-layer' above.

Region Code
Six region codes determine where you can watch your DVD. If you purchased a DVD in Sydney, you won't be able to watch it in Paris. See 'region protection' below for more info.

Region Protection
Region Protection is encoded onto .VOB files. Some Rippers offer you the ability to Rip out Region protection during normal Ripping. Once Ripped this way, the files will play in any DVD player, and will not have Region protection problems. Read our FAQ on Region Codes for more info.

Ripper
A Ripper is a program that allows you to break the DVDs encryption and "rip" out the files from the DVD, without it being turned into meaningless data. Basically, it allows you to copy files from the DVD to your hard drive successfully.

Ripping
This means copying a DVD movie to your hard drive. This includes the authentication process for the DVD Drive and the actual CSS Descrambling. The term "Ripping" is often confused with the entire process of descrambling a DVD and then converting the audio and video into another format, which it is not.

ROM
Read Only Memory: cannot be written to.



Streamlist
A streamlist is an ASCII test file that contains the pathnames and filenames of your VOB files, one file on every line. Here's a small example:
e:\video_ts\vts_01_1.vob
e:\video_ts\vts_01_2.vob
e:\video_ts\vts_01_3.vob
e:\video_ts\vts_01_4.vob
e:\video_ts\vts_01_5.vob

Save this file as streamlist.txt, or streamlist.lst. Make sure that you save it as unformatted ASCII text, I suggest you use notepad to edit your streamlists, since notepad won't save in another format. Mpeg2avi needs the streamlist to have the extension lst, whereas you're free to chose any other extension for other programs that use a streamlist. However the GUI is kind of limited in its choice for input files/extensions, therefore you might have to rename your streamlist, if it doesn't show up in the file selection dialog.

Surround Sound
One of the most high-fidelity sound protocols available for the home user. It allows you to hear a car moving from behind you to in front of you. Also known as positional sound.

SVCD
Super Video CD.This format is mainly used in Asian countries. It uses MPEG2 Video and has a high quality, LaserDisc-like appearance and also offers high quality surround sound. Additionally, it can take advantage of hardware decoders and there are players for many operating systems. However there are only a few, mostly Asian made low-end DVD players that can play SVCD and other than specific SVCD players which are not sold in the United States and in Europe you can only play SVCDs on your computer. The video is MPEG2 at up to 2600kbit/s and audio MPEG1 audio layer 2 up to 224kbit/s. MPEG2 multichannel audio is also possible but can only be encoded on Linux.

VBR
Variable BitRate. It's possible to encode both audio and video in VBR mode, which won't use the same bitrate for the whole file (as in CBR = Constand BitRate) but rather more complicated parts of the video/audio will receive more bitrate in order to look/sound better and less demanding parts will get less bitrate.

VCD
Video CD.This is a CD that is created to play on CDi and Video CD players and works on many DVD players along with the ability to play on software players on almost every operating systems. VCD does not require a fast computer but the image is VHS-like. The video is MPEG1 at 1150kbit/s and audio MPEG1 audio layer 2 at 224kbit/s.

VKI
Variable Keyframe Interval. Basically that means that keyframes will not be inserted in regular intervals as in the regular DivX codecs but where they are needed. There are 2 ways of VKI: The first is that the encoder analyzes the compressed frame, compares it against the original and reencodes the frame again as a keyframe if the quality difference is higher than a set threshold. This way of encoding is only possible with a certain special application: m4c. There's a command line based version and a plugin for AviUtl available (the latter is described in detail in the AviUtl guide). If you set the treshold too high you'll end up with a lot of keyframes. Then there's the 2nd way which is basically keyframe insertion at scene changes. In order to do that the encoding program or the codec will detect when there's a cut (as it's called by movie makers) occurr and make the first frame of the new scene a keyframe. This can be achieved by using mpeg2aviAr (part of AviRevolution 2.1), m4c or by installing the DivX VKI codec. If you use the latter you don't have to worry about the encoder... every program that can encode to DivX will then result in files that has keyframes at scene changes. VKI, when properly used (that applies to the first way), can help you increase quality and reduce the amount of keyframes, which may lead to higher quality again because especially at lower bitrates too many keyframes will give you a worse quality.

VM2
Short version of VKI + MM4 + VBR MP3

VOB Files
.VOB files are the default format of DVD movies. These files may contain several streams of audio/video which are "multiplexed" together (for example, the chapters/language selections). These files, once they are Ripped , can be played back with any DVD player software that supports the file opening feature. .VOB files have a specific naming standard located between the VTS and the .VOB where the first set of numbers stand for the Title number and the second set stands for the Section number. (Example - vts_01_1.vob). The whole movie is usually contained within one title while the rest of the titles contain extras such as bonus tracks, trailers , etc. Video_ts.vob usually contains the main menu information. Each section of the title cannot exceed 0.99GB in size.

XVCD
VCD's need to be a certain size and format to be played back on a standalone DVD or SVCD player. If they do not follow these rules they are called eXtendec Video CD's. This is not an official format.

Added:  Tuesday, October 01, 2002
Reviewer:  Ed

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