Audio Video Interleave

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5249.4646.xxxx.xxxx 4156.4920.4C49.5354 hex RIFF .... AVI LIST ( ASCII)

Audio Video Interleave ( AVI) is a defined by the software manufacturer Microsoft video container format that is derived from the introduced for Windows 3.1 RIFF ( Resource Interchange File Format). "Audio Video Interleave " means that audio and video data interlocked, so " interleaved " are saved ( See also interleaving ).

General

The first definition of AVI is as old as multimedia PCs. The format was created by Microsoft in 1992 as part of the Video for Windows API to allow playback of audio-visual data within Windows. In an AVI file multiple video, audio and text subtitle streams can be present, which may be encoded by different methods in turn. The type of a video stream is stored on FourCCs (Four Character Code ), for audio streams come TwoCCs used. To encode or decode a corresponding codec is required for each stream. Most AVI files use the extensions, which were presented by the Matrox OpenDML group in February 1996. These files are supported by Microsoft to a limited extent and are unofficially known as AVI 2.0.

Advantages of AVI

  • The AVI format is widely used and is at least sufficiently supported by most multimedia programs.
  • The format is also supported by a large number of DVD players (if the codecs used are supported by this ).

Disadvantages of AVI

  • No standardized way to store the aspect ratio, which playback software can not automatically select the correct
  • Not designed for video and audio formats, variable frame - (VFR ) and data rate ( VBR) revise the
  • Not intended for video compression that use images that lie in front of the currently displayed (MPEG- 4, ...)
  • Poor support for subtitles ( subtitles as images, such as DVDs, are not possible)
  • No support from menus or chapters
  • No uniform way to specify timestamps ( time code )

Some of these limitations can be circumvented sometimes. Thus, for example, enables the encoder to use FFmpeg Vorbis audio in AVI files. Most but not without disadvantages such as greatly increased data traffic ( overhead) or incompatibility with hardware or software.

This led to the development of other new container formats like Matroska, Ogg Media or the MP4 container format.

Construction

An AVI 1.0 file consists of a RIFF file with a single AVI - list, an AVI 2.0 file contains additional AVIX lists. Each AVI and AVIX list is not larger than 2 GB. In the case of AVI 2.0 file requires the specification that the first RIFF list does not exceed 1 GB. This point is ignored by some applications when creating such files. The AVI LIST contains a list with the headers, a list of the actual data and an optional chunk for index entries.

An AVI file usually contains one image in a block, called chunk. Deviating from multiple images can be housed together in a chunk, if specified in the header that the index must necessarily be used to find the pictures.

This index is usually contained lists all frames (video, audio, subtitle ) with position and size. For AVI 1.0 it is not necessarily required. Timestamps are only implied. In the case of AVI 1.0, the index is at the end of the file, in the case of AVI 2.0 is a two-stage index used. The first stage is then for each stream in the header of this stream, the second stage is located in the middle of the video / audio data. The block size for the second stage of the index is not specified, format of technical reasons, but at least one block per stream and per 4 GB must be present. Since a file can only be played correctly in some cases when this information is available, especially if parts of the data stream are corrupted AVI is unsuitable as a streaming format.

The header can also be stated that the index must be used to find data blocks. This is relevant if the data is not within the AVI file in the playback order, or there are multiple frames, such as multiple images in a single chunk. Packing multiple images in one chunk to save overhead allowed, because each chunk pulls, not counting an index entry, 8 bytes overhead by itself, but reduces the chance of being able to play undamaged parts partially damaged files.

Because the AVI format on the x86 architecture has its origin, the figures contained therein, in little- endian format are kept.

Audioformat Indeo Cinepak Technical standard
18315
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