Codec

As Codec ( portmanteau word from English- coder and decoder ), we describe a method, data or signals digitally encoded and decoded. In the direct conversion from one format to another (eg, MPEG-2 to MPEG -4 or MP3 to WMA) is also called transcoding.

General

Most often, the analog signals are not digitized loss in coding process, but is carried out a dynamic reduction of the analog signal and a data compression of the digital signal, which leads, depending on the degree and method for quality loss during the reconversion of the digital data stream into the analog signals. Picture and sound quality can be affected, but also the continuity of the playback. Therefore a reduction of the necessary for the transmission of the digital signal bandwidth is achieved, or a reduction of the necessary storage capacity for the storage.

Furthermore, it is important to distinguish between the coded data format, that is, the audio format and the video compression used, and on the other hand to the container format. For example, created the famous XviD MPEG-4 video tracks or MP3 Audio Codec MP3 audio tracks. These two classes can be combined in a file container (eg AVI) and then stored.

In the international telephone networks, a large number of different codecs is used; while the fixed and mobile telephony with a few codecs, the G- series of ITU- T works (for example, G.711 or G.726 ), there is a great diversity of mobile phones in the access to the mobile networks. Many coding have been standardized by the International Telecommunication Union, among others, worked out by the MPEG method such as the video format MPEG -4 AVC aka H.264. To enable communication between devices that operate their devices with different codecs, is a conversion into each other format, transcoding is required. For telephony via the Internet, IP telephony, it does not constitute a major technical hurdle to master all the methods and their transcoding.

List of common codecs with appropriate program implementations

Video Codecs

Audio Codecs

  • MP3 codec of the Fraunhofer-Gesellschaft
  • Psytel AAC ( predecessor of Nero Digital Audio)
  • FAAC (AAC encoder) and FAAD2 (open source decoder)
  • FFmpeg AAC
  • Vorbis
  • Opus

Voice codecs

  • Advanced Multi - Band Excitation ( AMBE )
  • AMR
  • Code Excited Linear Prediction ( CELP )
  • GSM
  • Internet Low Bitrate Codec ( iLBC )
  • ITU standards: G.711 or G.711a and G.711u
  • G.722
  • G.722.1
  • G.722.2
  • G.723.1
  • G.726
  • G.728
  • G.729 and G.729.1

Codec collections

  • Libavcodec library from the FFmpeg project with implementations of various audio and video codecs, like FLAC, MP3, WMA, WMV, MPEG-1/2/4, Huffyuv
  • Nero Digital: MPEG -4 Part 2 ASP video codec, H.264 video codec, AAC audio codec LE, HE- AAC audio codec
Bandwidth (signal processing) Audioformat Comparison of video codecs LAME Fraunhofer Society RealAudio Multi-Band Excitation ABX-Test Data compression#Audio Image compression Digital container format Mean Opinion Score
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