G.729
G.729 is a narrowband audio codec at 8 kbps — one-eighth the bandwidth of G.711, useful for satellite, mobile, or constrained-network links. Patent royalties expired in 2017, so it is now royalty-free.
Specs
- Sample rate: 8 kHz
- Bitrate: 8 kbps (Annex A: 6.4 kbps low-rate, Annex B: VAD/CNG silence suppression)
- Frame: 10ms (typical packetization 20-30ms = 2-3 frames per RTP packet)
- MOS: ~3.9 (vs 4.2 for G.711)
When to use it
- Satellite or mobile-data links where bandwidth is the bottleneck.
- Branch offices on slow VPNs.
- Not recommended as a default — the bandwidth difference is rarely worth the quality drop on modern broadband.
Transcoding cost
G.729 is more CPU-expensive to encode/decode than G.711. PBX-to-carrier traffic in G.729 forces the carrier to transcode for the PSTN side, which can degrade quality further. Prefer G.711 unless you have a measurable bandwidth constraint.
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