WhatsApp uses the Opus audio codec for voice calling.
Opus was designed for interactive, real-time audio such as internet calls, conferencing, and games. It combines two approaches: the SILK technology suited to speech and the CELT technology suited to higher-quality general audio. This lets Opus operate across a wide range of bit rates while keeping latency low.
The codec was developed through collaboration involving the Xiph.Org Foundation and Skype engineers, then standardized by the Internet Engineering Task Force in RFC 6716 in 2012. It is royalty-free, an important advantage for large communications platforms.
Speex and Vorbis are related open audio technologies, but neither is WhatsApp’s standard voice-call codec. AAC is widely used for music and video, yet it is not the canonical answer for WhatsApp voice calling. Opus should also not be confused with a transport protocol: it compresses audio, while RTP carries media packets across a network.