Acodec is a computerhardware orsoftware component that encodes ordecodes adata stream orsignal.[1][2][3]Codec is aportmanteau ofcoder/decoder.[4]
In electronic communications, anendec is a device that acts as both an encoder and a decoder on a signal or data stream,[5] and hence is a type of codec.Endec is aportmanteau ofencoder/decoder.
A coder or encoder encodes a data stream or a signal for transmission or storage, possibly inencrypted form, and the decoder function reverses the encoding for playback or editing. Codecs are used invideoconferencing,streaming media, andvideo editing applications.
Originally, in the mid-20th century, a codec was a hardware device that coded analog signals into digital form usingpulse-code modulation (PCM). Later, the term was also applied to software for converting between digital signal formats, includingcompanding functions.
Anaudio codec converts analog audio signals into digital signals for transmission or encodes them for storage. A receiving device converts the digital signals back to analog form using an audio decoder for playback. An example of this is the codecs used in the sound cards of personal computers. Avideo codec accomplishes the same task for video signals.
When implementing theInfrared Data Association (IrDA) protocol, an endec may be used between theUART and theoptoelectronic systems.[6]
Examples of hardware codecs includeIntel QSV andAzalia Audio; examples of software codecs includeFfmpeg (and itsLibavcodec).
In addition to encoding a signal, a codec may also compress the data to reduce transmission bandwidth or storage space. Compression codecs are classified primarily intolossy codecs andlossless codecs.
Lossless codecs are often used for archiving data in compressed form while retaining all 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. This is especially true 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 is no longer 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.
Many popular codecs are lossy. They reduce quality in order to maximize compression. Often, this type of compression is virtually indistinguishable from the original uncompressed sound or images, depending on the codec and the settings used.[7] The most widely used lossy data compression technique indigital media is based on thediscrete cosine transform (DCT), used in compression standards such asJPEG images,H.26x andMPEG video, andMP3 andAAC audio. Smaller data sets ease the strain on relatively expensive storage sub-systems such asnon-volatile memory andhard disk, as well aswrite-once-read-many formats such asCD-ROM,DVD, andBlu-ray Disc. Lower data rates also reduce cost and improve performance when the data is transmitted, e.g., over the internet.
Two principal techniques are used in codecs, pulse-code modulation anddelta modulation. Codecs are often designed to emphasize certain aspects of the media to be encoded. For example, a digital video (using aDV 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 lowlatency between source encoding and playback. In contrast, audio codecs for recording or broadcasting can use high-latencyaudio 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 on small portable devices. For example, raw uncompressedPCM 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 asOpus and MP3.
Manymultimedia data streams contain bothaudio andvideo, and often some metadata that permits 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 acontainer format.
Lowerbitrate 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 eachtranscoding.
Audio Video Interleave (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 anISO standard. There are also other well-known container formats, such asOgg,ASF,QuickTime,RealMedia,Matroska, andDivX Media Format.MPEG transport stream,MPEG program stream,MP4, andISO base media file format are examples of container formats that are ISO standardized.
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Fake codecs are used when an online user takes a type of codec and installs viruses and othermalware into whatever data is being compressed and uses it as a disguise. This disguise appears as a codec download through a pop-up alert or ad. When a user goes to click or download that codec, the malware is then installed on the computer. Once a fake codec is installed, it is often used to access private data, corrupt an entire computer system or to keep spreading the malware. One of the previous most used ways to spread malware was fake AV pages, and with the rise of codec technology, both have been used in combination to take advantage of online users.[8] This combination allows fake codecs to be automatically downloaded to a device through a website linked in a pop-up ad, virus/codec alerts or articles as well.
above 5.0 – all sound artifacts will be beyond threshold of human perception with corresponding perception margin
