How to multistream without doubling your upload
Send one encode up and let the fan-out happen downstream. Multistreaming from your own computer sends a separate copy to each platform, so four destinations cost four times your upload. One encode upstream costs the same regardless.
Multistreaming sounds like a feature and is really a question about where the copying happens. Get that wrong and the number of platforms you can reach is capped by your broadband contract rather than by anything about your show.
The arithmetic of doing it locally
If your computer sends to each platform directly, it opens a separate connection for each one and sends the whole stream down all of them. A 1080p60 programme at 9 Mbps going to four platforms is 36 Mbps leaving your house, continuously, for the length of the show.
Most domestic connections cannot do that, and the ones that can will not do it while anybody else is home. Worse, the failure is not graceful: as the connection saturates, every destination degrades at once and the encoder starts dropping frames for all of them together.
Sending once instead
The alternative is to send a single encode upstream and let the duplication happen where bandwidth is not scarce. Your upload is 9 Mbps whether the show reaches one platform or six, and adding a seventh changes nothing about your connection at all.
The second benefit is less obvious and arguably larger: your machine encodes once instead of several times. Encoding is the expensive thing a computer does during a stream, and on a machine that is also running a game, four simultaneous encodes is the difference between a smooth show and a stuttering one.
What it costs
Each additional destination is five dollars a month, which makes adding a platform a decision you can test rather than commit to. If a channel does not repay the effort of being there, remove it and the cost goes away.
Encoding in the browser is free on every plan. The GPU-backed cloud encoder is metered instead: every plan includes a block of hours each month and charges for anything past it, so the shape of your schedule — four hours a week versus forty — matters more than the number of platforms.
The catch worth knowing before you wire up six
One encode means one set of settings, and those settings have to satisfy every destination at once. Because the programme is clamped down to the least capable platform enabled, one platform that will not take more than 720p live drags the entire simulcast down to 720p.
It is also worth being clear that only the video merges. Moderation, music policy, monetisation rules and takedown regimes stay separate, enforced by separate automated systems, and a strike on one platform tells you nothing about the next. Reach multiplies; so does exposure.
Put it to work on a real show
The whole page is this problem: one upload, five audiences, and chat from all of them in one panel.
Restream is the name most people reach for first. Worth reading if you want multistreaming plus a real scene canvas rather than either separately.
Outputs are priced individually, so the cost of a sixth platform is a number you can check before you add it.
Related guides
Because one encode has to satisfy every destination at once, the programme is clamped to the least capable one enabled. Switch on a service that caps live contribution at 720p and everything else receives 720p too.
Comfortably more than your target bitrate, sustained for the whole show. A 1080p60 programme at 9 Mbps wants real headroom above 9 at all times — not a speed test that touched 12 once on a quiet afternoon.
Four things generate cost: how many sources come in, how many go out, whether you encode in the browser or on a GPU, and how much recording you keep. Inputs and outputs are five dollars a month each.