Everything about Codec totally explained
» This article is on the compression/decompression algorithms used in digital media. For other uses of codec, see Codec (disambiguation).
A
codec is a device or
program capable of
encoding and/or
decoding a
digital data stream or
signal. The word
codec may be a combination of any of the following:
'compressor-
decompressor',
'coder-
decoder', or
'compression/
decompression algorithm'.
Description
Related concepts
An
endec is a similar yet different concept mainly used for
hardware. In the mid
20th century, a "codec" was hardware that coded analog signals into
Pulse-code modulation (PCM) and decoded them back. Late in the century the name came to be applied to a class of software for converting among digital signal formats, and including
compander functions.
In the recent software sense, codecs encode a data stream or signal for transmission, storage or
encryption, or decode it for viewing or editing. Codecs are often used in
videoconferencing and
streaming media applications. A video camera's
analogue-to-digital converter (ADC) converts its analogue signals into digital signals, which are then passed through a
video compressor for digital transmission or storage. A receiving device then runs the signal through a video decompressor, then a
digital-to-analogue converter (DAC) for analogue display. A "codec" is a generic name for a video conferencing unit.
An
audio compressor converts analogue audio signals into digital signals for transmission or storage. A receiving device then converts the digital signals back to analogue using an audio decompressor, for playback. An example of this are the codecs used in the sound cards of personal computers.
The raw encoded form of audio and video data is often called
essence, to distinguish it from the
metadata information that together make up the information content of the stream and any "wrapper" data that's then added to aid access to or improve the
robustness of the stream.
Compression quality
Most codecs are
lossy, which due to the reduced size of the resulting data stream achieve higher network transmission rates. Additionally, smaller data sets ease the strain on relatively expensive storage sub-systems such as
non-volatile memory and
hard disk, as well as write-once-read-many formats such as
CD-ROM,
DVD and
Blu-ray Disc.
There are also
lossless codecs which are typically used for archiving data in a compressed form while retaining all of the information present in the original stream. If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred. Especially if the data is to undergo further processing (for example
editing) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it's readily identifiable (visually, audibly or both). Using more than one codec or encoding scheme successively can also degrade quality significantly. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media.
Codecs are often designed to emphasise certain aspects of the media to be encoded. For example, a digital video (using a DV codec) of a sports event, such as
baseball or
soccer, needs to encode motion well but not necessarily exact colours, while a video of an art exhibit needs to perform well encoding colour and surface texture. There are hundreds or even thousands of codecs ranging from those downloadable for free to ones costing hundreds of dollars or more. This can create compatibility and obsolescence issues. By contrast, lossless PCM audio (44.1 kHz, 16 bit stereo, as represented on an audio CD or in a .wav or .aiff file) offers more of a persistent standard across multiple platforms and over time.
Many
multimedia data streams need to contain both
audio and
video data, and often some form of metadata that permits synchronisation of audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data stream to be useful in stored or transmitted form, they must be
encapsulated together in a
container format.
The widely spread notion of
AVI being a codec is incorrect as AVI is a
container format, which many codecs might use (although not to
ISO standard). There are other well-known alternative containers such as
Ogg,
ASF,
QuickTime,
RealMedia,
Matroska,
DivX, and
MP4.
Further Information
Get more info on 'Codec'.
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