SFU / MCU

What is it?

SFU and MCU are the two architectures for multi-person real-time video (the technology behind guest features):

• SFU (Selective Forwarding Unit): a smart relay — receives each participant's video and forwards copies to the others without altering them. Each person's device assembles the grid view itself.
• MCU (Multipoint Control Unit): a mixer — receives everyone's video, combines them into one composed picture on the server, and sends that single mix out.

A useful analogy: SFU is a mail sorting office (passes every letter along untouched); MCU is an editor who merges all the letters into one newsletter.

Practical example

A four-guest live show: with an SFU, each guest's device receives three separate video feeds and arranges them — flexible (each person could have a different layout) and cheap on server power, which is why modern video calling overwhelmingly uses SFUs. But the broadcast going out to the audience needs to be one single combined picture — so the show's layout (grid, spotlight) gets composed once, MCU-style, and that mixed feed is what flows to YouTube and the viewers. Most real products are hybrids: SFU among the participants, server-side mixing for the broadcast output.

Key things to know (non-technical)

• The trade: SFU = light on servers, heavy on each participant's device and bandwidth; MCU = heavy on servers (mixing costs computing), feather-light for everyone receiving.
• Guest count limits in products ("up to 10 on screen") trace directly to this architecture choice.
• The broadcast side of a live-studio product effectively requires a composed single feed — so "where does the mixing happen" (each host's phone vs the cloud) is a defining design decision.
• Cloud-side mixing also enables a weak phone to host a heavy show — the server does the lifting.

In Tupic Live

Tupic Live's guest architecture — SFU between participants, cloud composition of the final layout for broadcast — determines its guest limits, its phones' battery drain, and whether a mid-range Android can host an eight-person panel: invisible plumbing that defines visible product promises.