An MCU (Multipoint Control Unit) is a media server that decodes every incoming audio and video stream, mixes them into a single composite picture and audio track, and sends that one combined stream back to each participant. From the client's point of view a group call looks like a single incoming video, which makes client load predictable and keeps interoperability with older or constrained endpoints simple. The cost of that simplicity is borne by the server: mixing requires heavy CPU because every stream is fully decoded and re-encoded, and that extra encode-decode step adds a hop of latency to the conversation.
For telemedicine, the MCU's strengths line up with two specific situations. The first is producing a single composite recording of a multi-party consult, where you genuinely want one merged file rather than separate per-participant streams. The second is supporting low-power or legacy endpoints — older hardware, kiosks, or telephony bridges — that cannot handle decoding several independent streams at once.
In practice, most modern telemedicine architectures choose an SFU (which forwards streams without mixing) for live calls, and reserve MCU-style mixing for the narrower jobs of recording composition and legacy interop. Like an SFU, an MCU decrypts and re-encodes PHI-bearing media in the clear, so it must sit inside the HIPAA compliance boundary and be covered by a Business Associate Agreement (BAA) when a vendor runs it. The pitfall is defaulting to an MCU for everything and then paying for the latency and server cost on calls that never needed mixing.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
An MCU mixes everyone into one stream, which helps weak devices and recording but costs server CPU and flexibility. We wrote seven volumes covering the whole video stack, and for MCU decisions start with Volume 3: WebRTC, SFU and MCU topologies, players and delivery economics. Volume 5 covers recording and Volume 2 transport. Written by Nikolay Sapunov, CEO at Fora Soft.
MCU or SFU for group sessions and recorded consults?
We will compare MCU and SFU options for your session types and give you a topology recommendation with server cost estimates. 250+ video products shipped since 2005.
