A program or a device capable of performing encoding and decoding on a digital data stream or signal is known as Codec. The stream or signal for transmission, storage or encryption are encoded and decoded by the Codecs. In the video camera, the ADC converts its analogue signals to digital signals, which after passing through the video compressor for transmission or storage are decoded by the DAC for analog display. An audio compressor converts analogue audio signals to digital signals for transmission or storage. The de-compressor at the receiving end converts the digital signals back to analog for playback. Essence is a term commonly associated with the raw encoded form of audio and video data.

Codec is an algorithm used to code and decode the voice conversation in case of VoIP. The voice and sound that we hear is in analogue form and needs to be converted into a digital form for transmission over Internet. On the other side, it needs to be decoded once again to make it easy to hear for the recipient. The coding and decoding can be done in different ways by utilizing compression to reduce the bandwidth of the conversation. It is pertinent to mention that with VoIP, encoding with heavy compression takes more time and delays the conversation. It is here that the codec becomes eminent for it not only maintains good quality with compression but also does the encoding and decoding in a reasonable time.

Different VoIP clients support different codecs and each VoIP service provider supports the subset of a codec. In simpler terms when a VoIP call is established, you need to use a codec that is supported by both the parties and the provider. It is imperative to understand codecs so as to enable you to have a better understanding as to why some VoIP service providers are better than others and also why audibility through IPS with some service providers is better than others. In the following paragraphs, the different types of codecs and their utility are elaborated.

There are basically three types of codecs namely Audio codecs, Video codecs, and Data codecs.

Audio codec A computer program which compresses/decompresses digital audio data is known as audio codec. Most of these codecs are implemented as libraries that act as an interface to one or more multimedia players such as Winamp, XMMS and Windows Media Player. At times, the audio codec can refer to a hardware implementation or sound card. In such a context, the term audio codec actually refers to a combined audio AD/DA converter and a fine example of this would be the Intel Corporations AC97.

Video codec is the device or software module that enables the use of data compression for digital videos. Initially, videos were stored on magnetic tapes as an analogue signal. However with the evolution of compact discs, it became feasible to store and use video in a digital form. A combination of audio and video calls for customized methods of compression. There lies the complexity between video quality bit rate, the complexity of coding and decoding, robustness of data loss and error, random access and the art of compression.

The Digital video codec are found in DVD, VCD in emerging satellite and terrestrial broadcast systems and on the Internet. Online video encoding has led to the availability of codec packs with installer as a software package for PCs.

Data Codecs Data that is not automatically handled by quick time media operations and can be compressed and decompressed with the help of data codecs. Quick time media would automatically compress and decompress video and sound tracks with the help of image and sound codecs but it will not automatically compress or decompress sprites. Data codes are useful for compressing and decompressing sprites, 3D models and arbitrary blocks on data from other sources.