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11a. Multimedia Wrapper Formats (AVI & OGM)
Multimedia Wrapper Formats (AVI & OGM) [Keikai]
While the .AVI extension has often been associated with the MPEG4 codec, they are actually not the same thing. In fact, AVI files can contain codecs other than MPEG4 and there are MPEG4 codec encodes that are not ,AVI files.
.AVI files, amongst others, are wrapper formats that explain the multimedia content. They explain to the operating system what it will need to play the files. Also, they allow for synchronization between the video, audio, and other encoded information within a multimedia file, including subtitles. Modern implementations allow for multiple audio and subtitle tracks.
Nearly all multimedia files actually contain a wrapper as well and the encoded streams, however, some are not codec specific. Examples of codec specific wrapper files are .WMV, .ASF, .RM, and .QT. These are all discussed in their associated codec section of this FAQ.
.AVI (Audio-Video Interleave) Files [Keikai]
.AVI files are by far the most common multimedia file to be found in AB(M)A. And while they are generally associated with DivX files, they can actually contain streams encoded by any number of codecs. The codec(s) needed by the contained video and audio streams must already be installed to play any .AVI file. Therefore, it is necessary to be aware of what codecs an .AVI file needs. This information will often be provided by the poster of the file. If not, this FAQ lists other methods to determining the codec.
See the subtitle section for more information on displaying subtitles with AVI files.
. OGM (Ogg Media) Files [Orqyman, Keikai, xo, ed.]
Ogg Media (.OGM) files are a far more recent wrapper format than .AVI. Usually, they contain either DivX or XviD encoded video streams. .OGM files are becoming popular as they are far more adept at supporing multiple audio and subtitle streams than .AVI. As with .AVI files,you must have the codecs needed by the contained streams to play these files. Therefore, it is necessary to be aware of what codecs an .OGM file needs. This information will often be provided by the poster of the file. If not, this FAQ lists other methods to determining the codec.
Assuming the necessary video and audio codecs of the OGM file are known, and are already installed, it is also necessary to install the Ogg Vorbis Directshow filters available at http://tobias.everwicked.com/. Any DirectShow-compatible media play should then be able to play Ogg Media files. DirectX 8.0 or higher is necessary, as well.
When subtitles are encoded into the Ogg Media file, either DVobSub or SubTitDS is necessary to display them. The SubTitDS method will not work, however, for Windows 9x/ME users, and, therefore, DVobSub will be necessary.
See the subtitle section for more information on these DirectShow filters.
Some of the advantages of Ogg Media files over AVI files are:
Determining the codec inside a Wrapper FileTo be added later
User Contributed Notes