How to split stream audio from desktop audio on a Mac

To split stream audio from desktop audio on a Mac, you send the apps you want on stream to a virtual audio device — BlackHole is the free standard — capture that device in OBS, and add a Multi-Output Device so you still hear everything yourself. macOS has one master output, so without a virtual device your stream hears exactly what you hear. The split is a matter of deciding which apps go to the capture bus and which stay private, then keeping their levels balanced.

"Split stream audio from desktop audio" usually means one of two things, and they share the same fix. You want your viewers to hear a different mix than you do — copyrighted music muted from the broadcast but still playing in your ears, a Discord monitor kept out of the recording, alert sounds that never reach the stream. Or you want desktop audio as its own OBS track, separate from your mic, so you can balance it in post or on the fly. Both come down to routing: on a Mac, everything defaults to one output, so the moment you capture "desktop audio" you capture all of it. Splitting means peeling specific apps onto a bus that OBS listens to.

Why macOS makes this harder than it should be

Windows streamers can lean on the Volume Mixer and app-level routing that the OS ships. macOS gives you a single system output and no per-app view of it. There's no native "send this app to the stream and that one to my headphones." OBS can grab your default output, but that's an all-or-nothing capture — the same signal you're monitoring. To get two different mixes you have to build the split yourself with a virtual device, or hand the routing to an app that does it per application.

The free route: BlackHole + a Multi-Output Device

This is the setup most Mac streamers land on, and it costs nothing. BlackHole is a free, open-source (GPL-3.0) virtual audio driver from Existential Audio that passes audio between apps with zero added latency. It shows up as a normal output and input device, so OBS can capture whatever you send into it.

1. Install BlackHole (the 2ch build is fine for stereo) via its signed installer or brew install blackhole-2ch.
2. Open Audio MIDI Setup (in Applications → Utilities) and create a Multi-Output Device that includes both your real speakers or headphones and BlackHole. Put your real device at the top as the primary.
3. In System Settings → Sound, set output to that Multi-Output Device. Now everything you play goes to your ears and into BlackHole.
4. In OBS, add an Audio Input Capture source (or set Desktop Audio) to BlackHole 2ch. That's your stream's desktop feed.

That gets desktop audio onto the stream while you still hear it. The limitation is precision. A Multi-Output Device is a blunt copy — every app that hits your output lands in BlackHole, including the alert sounds and private apps you probably didn't want broadcast. To keep an app off the stream, you have to route that one app somewhere the Multi-Output Device can't see it, which means more devices and more Audio MIDI Setup surgery. OBS 30+ on macOS 13 and later can capture some app and device audio directly, which helps, but you're still hand-managing what goes where.

The paid tools, honestly compared

A few apps make the split cleaner, and they aim at different jobs. Here's the honest lay of the land so you can match the tool to what you actually need.

Loopback ($99) is the power tool: draw wires between apps and devices and build exactly the aggregate you want. If your routing is genuinely complex, it's worth it — but it's a lot of app for "keep music off the stream." Audio Hijack ($94) is built for recording and processing, not for riding levels live. SoundSource ($49) does per-app volume, per-app output, and EQ from a tidy menu-bar panel, and it's excellent — the reach is a mouse and a menu. All three are honest, well-built apps from Rogue Amoeba.

Where Fader fits — and where it doesn't

Be clear about this: Fader is not a virtual capture cable. You still install BlackHole (free) as the bus OBS listens to — Fader doesn't replace that piece. What Fader replaces is the tedious part: deciding which app goes to the stream bus and which stays in your ears, and then balancing all of it in real time. In Fader you point each app at an output device, so the apps you want broadcast go to BlackHole while your alerts, DMs, and monitor stay on your headphones only. No rebuilding aggregate devices in Audio MIDI Setup every time your setup changes.

The part that matters mid-stream is speed. When a track comes on that you can't broadcast, or a guest gets buried, you don't want to alt-tab into a menu and drag a slider on camera. Fader turns the keyboard into the mixer: hit a toggle hotkey and letter keys become per-app faders — one column per app — so you duck the music on the stream bus, push a guest up, or mute an app with a keystroke without leaving your scene. For a live show where the mix changes constantly, reaching the control in one keypress is the whole game. If your need is pure recording or one static aggregate you build once, the free route or Loopback may suit you better, and that's a fair call.

A practical split that works

A setup that holds up on air: route your music player, game, and browser to BlackHole so they hit the stream, and leave Discord, Mail, and system alerts on your headphones so they never do. Point OBS at BlackHole for desktop audio and add your mic as its own source. Now your viewers get game and music, you hear everything, and a copyright-flagged track is one hotkey from muted on the broadcast while it keeps playing for you. If you want the deeper walk-through of a no-hardware streaming rig, see the streamer's Mac audio setup without hardware, and for the routing mechanics on their own, how to send an app's audio to a different output on Mac.

Bottom line

Splitting stream audio from desktop audio on a Mac always comes back to routing, because macOS only gives you one output. BlackHole plus a Multi-Output Device is the free foundation and you should start there. The question is control: if you're happy hand-building devices for a static setup, the free route is enough. If your mix moves during the show and you want to assign apps and ride levels without touching the mouse, a keyboard-driven per-app mixer is what makes it fast — which is exactly what Fader is built for.