GOM Encoder


>> Glossary of Terms

This glossary page is designed to help users navigate through some of the more esoteric terms, technical jargon, and misinformation that may be making his or her video conversion endeavors more confusing than they need to be.


Put simply, encoding is the process by which information is converted into symbols for the purpose of transferring, encrypting, compressing, and / or storing.
The reverse of encoding, decoding is the process by which data that is represented by symbols is converted back into information that can be comprehended by the viewer.
Codec is a word derived from "coder-decoder" and is used to describe a device or computer program capable of encoding and decoding digital data ("encoding" for compression, storage, and encryption purposes and "decoding" for playback and editing). After being encoded, files are saved in certain compression formats (or standards) depending on the codec used. These formats are sometimes erroneously referred to as "codecs", but should not be confused with the encoding-decoding programs used to create them. Popular codecs include MPEG4, XVID, DIVX, and WMV for video and MP3, WMA, and AAC for audio.

- Reference / Read more: http://en.wikipedia.org/wiki/Codec
Container Format
In order to make a complete movie file, one must combine various audio, video, subtitle, and perhaps other data into a single file. File formats that specify how this kind of data (or other digital data) is stored are called Container Formats. Popular multimedia containers include formats such as AVI, MP4, MKV, WMV, and others. While such formats describe storage information, they do not describe how the data they contain is encoded. For example, a given AVI container file may contain audio and video data that is encoded at higher bitrates (and/or with different codecs) than another AVI file, despite the fact that the two files use the same .AVI extension. Likewise, a movie file using one container format may include audio and video data that is encoded in the exact same way as another movie file using a different container format. For this reason it is somewhat misleading to claim that one container format is higher quality than another container format.

- Reference / Read more: http://en.wikipedia.org/wiki/Container_format
DSC (Direct Stream Copy)
DSC (Direct Stream Copy) allows you to crop parts of a video file or change its container format while foregoing the decoding / encoding process used in normal conversion. This results in a much faster conversion, since all that is being changed is the length of the video or the package the video is contained in.
Frame Rate
Frame Rate refers to the speed (rate) at which unique images (frames) are displayed in a sequence; in other words, how often the picture on your screen changes. Frame rate is usually expressed in fps (frames per second). The most common frame rates for TV and movies are 24 fps, 25 fps, and 30 fps. While it seems logical to assume that the higher the frame rate the better the image will be, there is a limit to how many frames the human eye can perceive in a second, and therefore after a certain point it becomes impossible to tell the difference.

- Reference / Read more: http://en.wikipedia.org/wiki/Frame_rate
In the context of video compression, key frames are used to limit the amount of data that needs to be stored and make the compressed file as small as possible. With most video sources, the amount an image changes from frame to frame is minimal. Whenever a major change occurs, a key frame, or a frame that stores a complete image, is created. Between these key frames, only the small changes in the image are stored in the data stream.
Normalize Function
This function will equalize a file"s volume level to a set dB level. In other words, it will reduce the volume of exceptionally loud files and raise the volume of exceptionally quiet files to a standard volume level.
Bitrate refers to the speed at which data is presented per unit of time, often times measured in kilobytes per second (kbps) and megabytes per second (mbps). In relation to digital audio and video files, a higher bitrate is indicative of higher quality and larger file size. CBR, or Constant Bitrate, applies the same bitrate to the entire file when converting, regardless of the video content. Conversely, VBR, or Variable Bitrate, applies a low bitrate to sections of video with little movement and a high bitrate to sections with lots of movement. Using VBR therefore enables a user to create a high quality video that is relatively small in size.
FourCC, which stands for "Four Character Code", is when 4 bytes are used in order to uniquely identify a data format. Well known examples DIVX, XVID, and H264 (all of which identify which video codec was used for a given AVI file).

- Reference / Read more: http://en.wikipedia.org/wiki/FourCC
MP3 (Codec)
MP3, or MPEG-1 Audio Layer 3, is a very widely used lossy audio compression algorithm that was first introduced in 1993. Its purpose (as is true with any lossy audio codec) is to greatly reduce the file size of an audio recording while still producing a faithful reproduction of the original recording. To accomplish this, it cuts or reduces accuracy of audio data that is in frequency ranges considered to be beyond human auditory perception, and then encodes the remaining data as efficiently as possible. Files encoded with the MP3 codec use the ".mp3" file extension.

- Reference: http://en.wikipedia.org/wiki/Mp3
MP3P is an abbreviation for "MP3 Player", or a device designed to playback files saved in the MP3 format. Some confusion has been created by certain companies dropping the "P" and referring to MP3 Players as "MP3".
MP4 (Player)
As a result of erroneously labeling MP3P (MP3 Players) as "MP3", some Chinese companies started referring to MP3P with video playback support (like current generation iPods) as "MP4", intending to imply that they were more powerful MP3 Players with additional functionality. However, labeling these players as such causes them to be easily confused with the "MP4" container format.
MP4 (Container format)
MP4 container is a file format defined by MPEG standard and has the .MP4 extension. This format is supported by many companies including Apple and Sony, and is playable with iPod, PSP and etc.

- Reference: http://en.wikipedia.org/wiki/Mp4
MPEG4 (Codec)
MPEG-4 refers to a collection of compression standards for audio and visual data. MPEG-4 is divided into "parts", each of which covers a different compression aspect. The most widely used parts include MPEG-4 Part 2 (Divx, Xvid, 3ivx, Quicktime 6), MPEG-4 Part 10 (AVC/H.264, x264, HD video, Quicktime 7), and MPEG-4 Part 14 (.MP4 file format).

- Reference: http://en.wikipedia.org/wiki/Mpeg4
MS MPEG-4 (Microsoft MPEG-4) refers to a video codec implemented by Microsoft. Initially it could support the AVI format, but after Microsoft MPEG-4 Version 3 (Not to be confused with MPEG-4 Part 3) support was limited to the ASF (WMV) format. It appeared as though Microsoft was planning to abandon AVI to push WMV, which resulted in the creation of the DivX ;-) 3 codec. Currently, support for AVI has been added back into MS-MPEG4.
AVC, H.264, MPEG4 PART10 (Codec)
AVC, H.264, and MPEG4 Part 10 all refer to the same video compression standard. Currently it"s one of the most commonly used codecs for high-definition video and is one of the basic standards for Blu-ray Discs. Online streaming sources like YouTube and Vimeo also use H.264 for transmitting HD video.

- Reference / Read more: http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC
Baseline Profile
There are 17 "profiles" that define various compression capabilities when using H.264/AVC codecs. The Baseline Profile enables videos encoded in H.264/AVC to play correctly on some portable devices (like mobile phones).
AVI (Container format)
AVI (Audio Video Interleave) is a multimedia container format developed by Microsoft in the early 1990s, but is still used frequently to this day. AVI can store audio and video data that is encoded in almost any compression scheme, but lacks support for certain newer computer video techniques that the original specification didn"t anticipate. All of these drawbacks have been addressed by newer container formats such as MP4, MKV, and OGG.

- Reference: http://en.wikipedia.org/wiki/Audio_Video_Interleave
MKV (Container format)
MKV (Matroska Multimedia Container) is a free open-standard container format that is capable of holding an unlimited number of video, audio, picture, and subtitle tracks in a single file. Similar to other container formats like AVI, MP4, and ASF, but is completely open specification and is therefore has implementations in many open source software projects. It supports all known audio and video compression formats.

- Reference / Read more: http://www.matroska.org/technical/guides/faq/index.html
What would eventually become the current DivX codec began around 1998 when MS MPEG-4 Version 3 stopped supporting AVI. Annoyed by this, a French hacker decided to reverse engineer MS MPEG-4 Version 3, changing the FourCC from "MP43" to "DVI3" and distributing it as "DivX ;-) 3.xx"
About a year later, the hacker was recruited to help form a company (called DivXNetworks, Inc. intitally; now called DivX, Inc.) to create an MPEG-4 codec from scratch that would be backwards-compatible with MS MPEG-4 Version 3. The first release resulting from this effort was "OpenDivX".
The company split when an employee wrote a new and improved version of OpenDivX called "Encore 2", and a disagreement in the direction of the product occurred. Employees who wished to continue developing it as free and open-source left and started work on the Xvid project. The rest took the "Encore 2" encoding algorithm and developed the DivX 4.0 codec for commercial release in 2001. Currently DivX, Inc. continues to maintain and update the codec as needed.

- Reference: http://en.wikipedia.org/wiki/DivX
XVID (Codec)
When DIVX4 turned into a commercial project, XVID was derived as an opposition and to remain as an open source project. XVID is DIVX written backwards, and remains as an open source project.

- Reference: http://www.xvid.org
Theora (Codec)
Theora is a free lossy audio compression format developed by the Xiph.Org Foundation designed to compete with MPEG-4. It is most often used in conjunction with the OGG container format.
VORBIS (Codec)
Vorbis is an open source audio codec for lossy audio compression developed to compete with other popular specifications such as MP3, AAC, and WMV. Aside from its clear advantage of being completely free to use, modify, or implement at one"s own discretion, Vorbis encoding also tends to produce higher quality audio than other codecs at most bitrates. It"s sometimes referred to as Ogg Vorbis, as it commonly used in conjunction with the Ogg container format.

- Reference: http://www.vorbis.com
OGG (Container format)
OGG is a free open-source multimedia container format maintained by the Xiph.Org Foundation. Video layers are commonly provided by Theora with Audio layers by VORBIS (although other audio codecs such as Speex and FLAC are also supported). Previously all files that used the OGG container format were labeled with the ".ogg" file extension, but more recently the Xiph.Org Foundation created new extensions such as ".oga" for audio-only files, ".ogv" for video-only files, and ".ogx" for multiplex files (audio + video + subtitles etc).