G.729.1 is defined in ITU-T Recommendation G.729.1: “G.729 based Embedded Variable bit-rate coder: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729”
G.729.1 is an embedded variable bit rate coder with a core layer at 8 kbps interoperable with legacy G.729 coder.
The output of the G.729.1 coder has a bandwidth of 50-4000 Hz at 8 and 12 kbps (narrowband) and 50-7000 Hz from 14 to 32 kbps (wideband; 10 bit rates with a step of 2 kbps). At 8 kbps, G.729.1 is fully interoperable with G.729, G.729 Annex A and G.729 Annex B. Hence an efficient deployment in existing G.729 based VoIP infrastructures is foreseen. The coder operates on 20 ms frames and has an algorithmic delay of 48.9375 ms. By default, the encoder input and decoder output are sampled at 16 kHz.
The encoder produces an embedded bitstream structured in 12 layers corresponding to 12 available bit rates from 8 to 32 kbit/s. The bitstream can be truncated at the decoder side or by any component of the communication system to adjust "on the fly" the bit rate to the desired value with no need for outband signalling.
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