A description of the VOIP codecs G.723, G.711 and G.729, needs initially to provide a description of the use performed by codecs. A standard telephone call that utilizes VoIP architecture needs to pass through two separate environments which are not readily interoperable. The first environment belongs to the standard telephony service which is analog and will need to be converted to digital bitstream in order to progress along the digital environment without disruption to the signal.
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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.
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