Video Glossary

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for more information see AAC audio codec

(Advanced Audio Coding) AAC is the successor of AC3 audio. It is based on AC3 while adding a number of improvements in various areas.


for more information see AC3 audio codec

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


for more information see ASF container

(Advanced Streaming Format) Microsoft's answer to Real Media and streaming media in general.


for more information see AVI container

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

Aspect Ratio

for more information see Aspect Ratio

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for more information see bitrate

In digital multimedia, bitrate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors:

  • The original material may be sampled at different frequencies
  • The samples may use different numbers of bits
  • The data may be encoded by different schemes
  • The information may be digitally compressed by different algorithms or to different degrees

Generally, choices are made about the above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played.


for more information see Constant Bitrate

(Constant BitRate) It's possible to encode audio in CBR mode, which will use the same bitrate for the whole file.


for more information see codec

(COder/DECoder) a codec is a piece of software that allows you to encode something - usually audio or video - to a specific format and can decode the media encoded in this specific format again. Popular video codecs include; DivX, MPEG1, MPEG2, MPEG4, XviD, MKV,etc. The file file containers; AVI, ASF, MOV, etc. are not codecs but a file container that can be encoded using different codecs. Codecs are very important when it comes to digital video since unless it was compressed it would take Terabytes - thousands of Gigabytes to store a movie uncompressed. Since standard loss less compression is insufficient for video, the video codecs have to get rid of unimportant information, stuff the human eye won't see or is unlikely to see. Since that is still not enough modern compression algorithms use video keyframes, I and P frames in order to save space.


for more information see file container

A container is a construct to contain data - in this case video and audio data and possibly subtitles and navigational information. For instance, you would like to put a soundless video stream and the audio track together in one file. To do that you need a container format. Examples of container formats are: AVI, ASF, OGM, MOV, VOB, MKV, and MPG.


for more information see Display Aspect Ratio

(Display Aspect Ratio) DAR indicates the dimension of a screen. Most PC screens have a DAR of 4:3, meaning that the horizontal size is 4/3 as large as the vertical size. For TVs we have a lot of old 4:3 displays and more and more 16:9 displays. As you can guess from the numbers 16:9 displays are broader than 4:3 displays having the same diagonal size. 16:9 screens are more suited to display Hollywood movies which are usually shot with an aspect ratio of 1:2.35 or 1:1.85 (meaning that the horizontal size of the picture is 1.85 times as wide as the vertical size).


for more information see DivX video codec

There are 2 flavors of DivX today: DivX is the name of the hacked Microsoft MPEG4 codecs (Windows Media Video V3). Those codecs were developed by Microsoft for use in its 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 is remove that 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 latest releases of DivX also include a hacked Windows Media Audio Codec called DivX Audio.

The other DivX is a brand-new MPEG4 video codec developed by DivXNetworks. It offers much advanced encoding controls and 2 pass encoding. Furthermore the codec can play the old DivX (DivX3) movies. The codec is commonly called DivX4.


for more information see DTS audio codec

(Digital Theater System) DTS is an audio codec supporting multi-channel digital surround sound format used for both commercial/theatrical and consumer grade applications.


See file container.


for more information see 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.


for more information see video 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. Please note that a human eye cannot see more then 24 frames per second so going any higher is pointless.

Frame Rate

for more information see Frame rate



for more information see H264 video codec

H.264 is a codec for video compression, and is equivalent to MPEG4 Part 10. The intent of the H.264 project was to create a standard capable of providing good video quality at substantially lower bitrates.

I and P Frames

for more information see I and P frames

A video 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 video 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.


for more information see video keyframe

A complete video frame but heavily compressed.

Lossless Compression

for more information see Lossless Data Compression

Lossless data compression is a data compression algorithm that allows the exact original data to be reconstructed from the compressed data. The term lossless is in contrast to lossy data compression, which only allows an approximation of the original data to be reconstructed, in exchange for better compression rates.

Lossy Compression

for more information see Lossy Data Compression

A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way. Lossy compression is most commonly used to compress multimedia data (audio, video, still images), especially in applications such as streaming media and internet telephony.


for more information see MKV container

(Matroska Multimedia Container) MKV is an open standard free file container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks inside a single file. The most common use of .MKV files are used to store HD video files. It usually carries H.264 video, one or more AC3/AAC/DTS audio tracks and sometimes one or more subtitle tracks (sometimes coupled with one or more embedded TrueType or OpenType font).

Think of the MKV file container as a DVD in one file!


for more information see MOV container

A Quicktime file container.


for more information see MP3 audio codec

MPEG1 layer 3 audio codec. Please don't confuse it with a MP3 music file, MP3 is both a codec and a file container.


for more information see Motion Picture Expert Group

(Motion Picture Expert Group) MPEG is the 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. Files containing MPEG-1 or MPEG-2 video often use either the .mpg or .mpeg file container.


for more information see MPEG4

MPEG4 is pretty much a collection of standards defined by the MPEG Group, and it is the standard in digital video (mainly for picture phones, streaming media on the Internet and more). MPEG4 allows the use of different encoding methods, for instance a video keyframe can be encoded using ICT or Wavelets resulting in different output qualities.


for more information see MPG container

MPG can be either an abbreviation for MPEG or is used as a file container for MPEG-1 and MPEG-2 video data. It is a file container to contain MPEG-1/2 video stream and MPEG1 layer 2 audio (aka mp2 files). MPG file containers are also referred to as program streams.


for more information see OGM container

(OGg Media) Which is the name of the Ogg file container implementation by Tobias Waldvogel. OGM can be used as an alternative to the AVI file container and it can contain Ogg Vorbis, MP3 and AC3 audio, all kinds of video formats, chapter information and subtitles. Another alternative to OGM is MKV.

Real Media

for more information see Real Media

Real Media is a streaming media technology from RealNetworks. Real Media uses proprietary codecs developed by RealNetworks.


for more information see DVD Ripping

Basically ripping means copying a DVD movie to your hard disk. This includes the authentication process for the DVD Drive (try to copy a file off a DVD and you'll get a message that this operation is not supported if your drive hasn't been authenticated) and the actual CSS Descrambling. CSS (Content Scrambling System) is a copy protection scheme designed to prevent unauthorized copying of DVD movies, although many argue that it was also designed to control where DVD movies can be played since without a CSS license you essentially have to crack the encryption to play a DVD movie. The term ripping is also often used (even on this site) to describe the whole process of descrambling a DVD, then convert the audio and video into another lesser format.


for more information see Super Video CD

(Super Video CD) SVCDs are mainly used in Asian countries. They use MPEG2 Video and therefore have much better image quality, Laser Disc like and also offers High quality surround sound. Furthermore it can take advantage of hardware decoders and there are players for many operating systems. 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 most players will only output 2 channels and those that will pass through 5.1 audio still require that you have an MPEG2 multichannel capable receiver.


for more information see Variable Bitrate

(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 = Constant 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.


for more information see Video CD

(Video CD) VCDs work on many DVD players, there are software players on almost every operating systems, doesn't need a fast computer but the image is VHS-like. Video is MPEG1 at 1150kbit/s and audio MPEG1 audio layer 2 at 224kbit/s.

VOB Files

for more information see VOB container

All DVD movies are stored in so-called VOB files. Vob files usually contain either multiplexed Dolby Digital Audio or Digital Theater System audio and MPEG2 video. Vob Files are called as follows: vts_XX_y.vob where XX represents the title and Y the part of the title. There can be 99 titles and 10 parts, although VTS_XX_0.VOB does never contain any video, usually just menu or navigational information. There's 2 ways to find out which files contain the main movie: First: Play the movie in any DVD player and watch the LED on a standalone or the status window on a software player. Second: The main movie is the largest number of consecutively numbered VOB files. For instance it's vts_05_1.vob, vts_05_2.vob.... vts_05_8.vob.


for more information see Vorbis audio codec

Vorbis is a free and open source, lossy audio codec project headed by the Xiph.Org Foundation and intended to serve as a replacement for MP3. It is most commonly used in conjunction with the Ogg file container and is therefore called Ogg Vorbis.


WMV Codec

for more information see WMV Codec

(Windows Media Video) is a compressed video file format for several proprietary codecs developed by Microsoft. The original codec, known as WMV, was originally designed for Internet streaming applications, as a competitor to RealVideo.

WMV Container

for more information see WMV Container

A WMV file is in most circumstances encapsulated in the ASF container format.[ The file extension .WMV typically describes ASF files that use Windows Media Video codecs. The audio codec used in conjunction with Windows Media Video is typically some version of Windows Media Audio, or in rarer cases, the deprecated Sipro audio codec. Microsoft recommends that ASF files containing non-Windows Media codecs use the generic .ASF file extension.

Although WMV is generally packed into the ASF container format, it can also be put into the AVI or Matroska container format. The resulting files claim the .AVI, or .MKV file extensions, respectively. WMV can be stored in an AVI file when using the WMV 9 Video Compression Manager (VCM) codec implementation. Another common way to store WMV in an AVI file is to use the VirtualDub encoder.


for more information see XviD video codec

XviD is a word play, read it the reverse way and you might find a familiar term. XviD is an open source MPEG4 codec which depending on whom you're asking yields even better quality than the best DivX codec. The XviD homepage can be found here.