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Collaboration, Voice & AV · Intermediate

Multipoint Control Unit (MCU)

A conference bridge that decodes, mixes and re-encodes audio and video from multiple participants into composite streams.

Definition

MCUs transcode each participant's stream to create continuous presence layouts and can adapt resolution and codecs for each endpoint. Transcoding adds latency and needs significant DSP or CPU resources. Modern cloud services often use SFU architectures instead, although transcoding is still used for interop with legacy endpoints.

Example

A legacy H.323 room system joins a meeting through an MCU that sends it a 2x2 composite layout.

Exam tip

MCU equals transcoding and compositing; SFU equals forwarding without decoding.

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