Codec

This article is about encoding and decoding a digital data stream. For other uses, see Codec (disambiguation).
Further information: List of codecs and Video codecs

A codec is a device or computer program for encoding or decoding a digital data stream or signal.[1][2][3] Codec is a portmanteau of coder-decoder or, less commonly, compressor-decompressor.

A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Codecs are used in videoconferencing, streaming media, and video editing applications.

Related concepts

In the mid 20th century, a codec was a hardware device that coded analog signals into digital form using pulse-code modulation (PCM). Late in the century the name was also applied to a class of software for converting between different digital signal formats, including compander functions.

A modem is a contraction of modulator-demodulator. The telecommunications industry referred to the device as a dataset. It converts digital data from computers to analog signals for transmission over telephone lines. On the receiving end the analog signal is converted back to digital data.

An audio codec converts analog audio signals into digital signals for transmission or storage. A receiving device then converts the digital signals back to analog using an audio decompressor, for playback. An example of this is the codecs used in the sound cards of personal computers. A video codec accomplishes the same task for video signals.

Compression quality

Media codecs

Two principal techniques are used in codecs, pulse-code modulation and delta modulation. Codecs are often designed to emphasize certain aspects of the media to be encoded. For example, a digital video (using a DV codec) of a sports event needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to encode color and surface texture well.

Audio codecs for cell phones need to have very low latency between source encoding and playback. In contrast, audio codecs for recording or broadcast can use high-latency audio compression techniques to achieve higher fidelity at a lower bit-rate.

There are thousands of audio and video codecs, ranging in cost from free to hundreds of dollars or more. This variety of codecs can create compatibility and obsolescence issues. The impact is lessened for older formats, for which free or nearly-free codecs have existed for a long time. The older formats are often ill-suited to modern applications, however, such as playback in small portable devices. For example, raw uncompressed PCM audio (44.1 kHz, 16 bit stereo, as represented on an audio CD or in a .wav or .aiff file) has long been a standard across multiple platforms, but its transmission over networks is slow and expensive compared with more modern compressed formats, such as Opus and MP3.

Many multimedia data streams contain both audio and video, and often some metadata that permit synchronization of audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data streams to be useful in stored or transmitted form, they must be encapsulated together in a container format.

Lower bitrate codecs allow more users, but they also have more distortion. Beyond the initial increase in distortion, lower bit rate codecs also achieve their lower bit rates by using more complex algorithms that make certain assumptions, such as those about the media and the packet loss rate. Other codecs may not make those same assumptions. When a user with a low bitrate codec talks to a user with another codec, additional distortion is introduced by each transcoding.

AVI is sometimes erroneously described as a codec, but AVI is actually a container format, while a codec is a software or hardware tool that encodes or decodes audio or video into or from some audio or video format. Audio and video encoded with many codecs might be put into an AVI container, although AVI is not an ISO standard. There are also other well-known container formats, such as Ogg, ASF, QuickTime, RealMedia, Matroska, and DivX Media Format. Some container formats which are ISO standards are MPEG transport stream, MPEG program stream, MP4 and ISO base media file format.

Telephony Codec

See also

Comparisons

References

  1. "Using codecs". Microsoft. Retrieved 2009-12-21.
  2. "About.com - Codec". About.com. Retrieved 2009-12-21.
  3. "Ubuntu Documentation - What is a codec?". Ubuntu Documentation Team. Archived from the original on February 19, 2012. Retrieved 2009-12-21.
  4. "Audio quality of aac vs. mp3 vs. wma vs. ogg encoders". SoundExpert. Retrieved 2010-07-25. above 5.0 – all sound artifacts will be beyond threshold of human perception with corresponding perception margin
This article is issued from Wikipedia - version of the Wednesday, March 30, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.