How to Build an App Like Zoom

Why mesh fails past three people

The simplest WebRTC topology has everyone send their stream to everyone else. With N participants each device uploads N-1 streams.

At four people that's three uploads per device — already beyond typical home upstream bandwidth, and punishing on mobile CPU and battery. Mesh is viable for one-to-one and nothing more.

SFU is what production uses

A Selective Forwarding Unit means each participant uploads once to a server that forwards streams to everyone else. Upload cost becomes constant regardless of participant count.

What the SFU then has to do well is where the difficulty lives:

Simulcast — clients publish several quality layers so the server can send each receiver an appropriate one
Bandwidth estimation per receiver, adapting continuously as networks change
Active speaker detection, so you forward the streams that matter rather than all of them
Packet loss recovery through retransmission and forward error correction
Geographic distribution, because a call routed through the wrong region adds latency nobody can fix client-side

Each of those is a specialist domain. Together they're why video infrastructure companies exist.

The parts people forget

TURN servers. Roughly a fifth of connections can't establish peer-to-peer through NAT and firewalls, and must relay. TURN relay bandwidth is a real, ongoing cost.

Recording means server-side composition of multiple streams into one file — CPU-heavy, storage-heavy, and it creates retention and consent obligations, especially in regulated settings.

Echo cancellation and noise suppression. Browsers provide baseline processing; the perceived quality gap between adequate and excellent audio is larger than for video, and audio problems end calls faster than video problems.

What to demand from a provider

Since you should almost certainly buy — Daily, LiveKit, Twilio, Agora, Vonage — evaluate on: SFU with simulcast, geographic coverage matching your users, recording controls and where recordings are stored, graceful degradation to audio-only, a BAA if healthcare is in scope, and transparent per-minute pricing.

LiveKit is worth noting as open source, so self-hosting stays available if per-minute economics eventually stop working.

When building is defensible

Only when video is the product and you have differentiated requirements — unusual codecs, very large broadcasts, or specialised low-latency needs — plus the team to own it. For a telemedicine, education, or support product, video is a component and buying is correct.

Related builds

How to build a telemedicine app — BAA-covered video in a clinical flow
Best video SDK for telemedicine apps
How to build an eLearning platform

FAQ

Why can't you build group video with plain WebRTC?

Mesh topology has every participant upload a stream to every other, so four people means three simultaneous uploads per device — beyond typical home upstream bandwidth and punishing on mobile CPU. Production uses an SFU, where each client uploads once to a server that forwards streams, making upload cost constant.

Should I build or buy video infrastructure?

Buy, unless video itself is your product and you have differentiated requirements plus a team to own it. Simulcast, per-receiver bandwidth estimation, packet loss recovery, TURN relay, and geographic distribution are each specialist domains — which is precisely why video infrastructure companies exist.

What should I look for in a video SDK?

SFU with simulcast, geographic coverage matching your users, recording controls including where files are stored, graceful degradation to audio-only on poor networks, a BAA if healthcare is in scope, and transparent per-minute pricing. LiveKit is worth noting as open source, keeping self-hosting available if per-minute economics stop working.