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A codec ( syllable word from English co der , German encoder , and dec or , German decoder ) is a pair of algorithms that digitally encodes and decodes data or signals. Direct conversion from one format to another (e.g. MPEG-2 to MPEG-4 or MP3 to WMA) is called conversion or, in the case of audio and video files, also called transcoding . Colloquially, the use of the term codec has also become established for the integrated circuits that do the coding.


In most cases, the analog signals are not digitized without loss during the encoding process, but instead the analog signal is dynamically reduced and the digital signal is compressed , which, depending on the extent and method, leads to quality losses when converting the digital data stream back into the analog signals. Picture and sound quality can be affected, as can the continuity of playback. This results in a reduction in the bandwidth required for the transmission of the digital signal or a reduction in the storage capacity required for storage.

It is also important to differentiate between the encoded data format, i.e. the audio format and the video compression used , and the container format . For example, the well-known XviD codec created MPEG-4 -Videospuren or MP3 audio codec MP3 -Audiospuren. These two classes can be combined in a file container (e.g. AVI ) and then saved.

A large number of different codecs are used in international telephone networks ; While fixed and mobile network telephony works with a few codecs of the G series from ITU-T (for example G.711 or G.726 ), there is a great variety of mobile phones in the area of ​​access to mobile networks. Many coding methods have been standardized by the International Telecommunication Union , including those developed by the MPEG such as B. the video format MPEG-4 AVC also known as H.264 . In order to enable communication between participants whose end devices work with different codecs, conversion into the other format, i.e. transcoding, is required. For telephony over the Internet, IP telephony , it is still a major technical hurdle to master all procedures and their transcoding.

List of common codecs with corresponding program implementations

Video codecs

Audio codecs

Speech codecs

Codec collections

  • libavcodec : Library from the FFmpeg project with implementations of various audio and video codecs, for example for FLAC, MP3, WMA, WMV, MPEG-1/2/4, Huffyuv
  • Nero Digital : MPEG-4 Part 2 ASP video codec, H.264 video codec, LE-AAC audio codec, HE-AAC audio codec

See also

Web links