Turn any audio input or the apps themselves into a live stream: low-latency HLS, AAC, MP3, FLAC and raw PCM,
from a menu bar app, on your network or on your own domain with HTTPS.
Off air it tells you whether everything is set. On air it is a control room. Settings slide in and out of the same window.
Streaming your Mac's audio somewhere else usually means Icecast, OBS or a paid service, and several seconds of delay. MicroCast is the small tool in between: pick an input such as Elgato's Wave Link Stream mix, press Start, and share a link. Listeners get a page that plays in about a second over HLS, or in 200 ms uncompressed on a connection that can carry 1.5 Mbit/s, and hi-fi players get plain AAC, MP3 or lossless FLAC URLs.
- Any input: every Core Audio device, virtual ones included (Wave Link, BlackHole, Loopback, aggregate devices…), captured at 48 kHz stereo.
- Or the apps themselves: capture the output of chosen running applications, or of everything, through a system audio tap, optionally mixed with an input. No virtual audio driver needed.
- Low-Latency HLS with one AAC rendition per bitrate (64, 128, 256 and 320 kbps by default, configurable), partial segments, blocking reloads and preload hints. About 1.3 s in hls.js on a LAN.
- Direct streams for real players: AAC, MP3, FLAC (lossless) and raw PCM, with
icy-name, ID3 and Vorbis tags so the stream name shows up in VLC, mpv or foobar2000. - Now-playing title: a pattern like
%name% - Now playing: %artist% - %title%, shown live as the ICYStreamTitlein VLC, mpv and foobar2000, and in the browser tab. - A player page served by the app: hls.js, quality selector, live latency and level, an ultra-low-latency PCM mode (~0.2 s, uncompressed), direct links, a listener graph, the track playing in Music or Spotify with its artwork, light and dark, lock-screen controls and Add-to-Home-Screen on phones.
- Screen streaming: capture a display or a region of it and show it on the page as low-latency MJPEG, with cinema mode and full screen. No audio sync, it's a visual companion.
- Jingles: drop audio files in a folder; one plays over the music at every track change in Music or Spotify — or every few tracks, your call — and on demand from a button. The music fades to a set level and comes back, radio style.
- Always there: the address stays online between streams with an off-air page that starts playing by itself the moment you go live, so listeners can keep it bookmarked.
- Internet in one click through Cloudflare (no account needed), ngrok, Tailscale Funnel or any command that prints a URL, with an optional password. Or your own domain, free: DuckDNS keeps a fixed name pointed at your router and the app serves HTTPS with a Let's Encrypt certificate it obtains and renews itself.
- Record while streaming to FLAC, AAC or MP3 in
~/Music/MicroCast. - Menu bar app: a stereo level trace, one-click start, QR code and share sheet for the addresses, a listener graph
with peak, a Settings window,
Bonjour advertisement,
hostname.locallinks, launch at login and auto-start. - No third-party Swift dependencies: AVFoundation, AudioToolbox, Network.framework and SwiftUI only.
Download the DMG from the releases, drag MicroCast to Applications, launch it: it lives in the menu bar as a radio icon. macOS asks once for microphone access, which is how it gates every audio input, and once for System Audio Recording when you capture applications.
The DMG is signed ad hoc, so Gatekeeper will complain on first launch: right-click → Open, or
xattr -d com.apple.quarantine /Applications/MicroCast.app
Or build it yourself (macOS 14.2+, Xcode command line tools):
git clone https://github.com/eko/microcast.git
cd microcast
./run.sh
MP3 needs lame (brew install lame); everything else uses codecs built into macOS.
- Click the radio icon in the menu bar. The window opens and stays open. It has no title bar buttons: click the icon again, or press ⌘W, to put it away — either way MicroCast stays in the menu bar rather than quitting, and the next click brings the same window back, same place, same screen you left it on. Drag it by its background. Press Start streaming. Wave Link Stream is selected by default when present; pick another input, or switch Capture to Running applications and tick the apps you want, in Settings → General (⌘,).
- Off air, the dashboard is a pre-flight panel: source, formats, address and jingles, each row telling you whether it looks usable and taking you straight to the setting that changes it. On air it becomes the control room — a rolling stereo trace of the output with peak-hold marks, uptime and listener count, the current track with its cover, and the addresses to share: copy, AirDrop to your phone with the share button, open in the browser, or scan the QR code.
- The gear slides the same window over to Settings; the chevron, or Escape, slides it back. Settings hold the stream name and port; under Stream the HLS part and segment lengths (shorter = lower latency, more requests), which formats to produce (HLS, AAC, MP3, FLAC, PCM) and the list of bitrates; recording; and under Internet the tunnel and password. Changes apply on the next start; while live, the dashboard offers a one-click restart.
- Right-click the menu bar icon for start/stop and a jingle without opening the window.
| Give this to… | URL |
|---|---|
| anyone with a browser | http://<mac>.local:8080/ |
| VLC, mpv, foobar2000, a smart speaker | http://<mac>.local:8080/stream.flac or /stream-256.mp3 |
| an HLS player, a website, OBS | http://<mac>.local:8080/hls/master.m3u8 |
| ffmpeg, sox, your own code | http://<mac>.local:8080/stream.pcm |
The full list, headers and formats are in docs/STREAMS.md.
| Path | Measured |
|---|---|
| Page, ultra-low-latency mode (uncompressed, 1.5 Mbit/s) | ~0.2 s |
| Page, LL-HLS, same network (334 ms parts) | 1.3 s |
| Page, LL-HLS through a Cloudflare tunnel | 2–3 s |
| VLC or mpv on a direct stream | 1–2 s |
Pick a tunnel under Settings → Internet. Cloudflare's quick tunnel needs no account and gives a random
trycloudflare.com address; a named tunnel gives you a stable hostname on your domain; ngrok and Tailscale
Funnel work too, and Custom command runs anything that prints an https:// URL. If you can forward a port on
your router, DuckDNS + HTTPS gives you a free fixed name (or your own hostname via CNAME) with a real
certificate and no buffering, and Own hostname + HTTPS does the same with a name your box already keeps
current. Set a password before you share the link. Details and measurements in
docs/TUNNELS.md.
flowchart LR
A[Audio device] --> B[AVCaptureSession<br/>48 kHz s16le]
B --> C[AVAssetWriter ×4<br/>fMP4 parts] --> D[LL-HLS playlists]
B --> E[AudioConverter<br/>AAC ×4, FLAC]
B --> F[lame ×4<br/>MP3]
B --> G[PCM chunks]
D & E & F & G --> H[HTTP server<br/>Network.framework]
H --> I[Browsers, players, tunnel]
Capture, encoding, packaging and serving all live in one process. docs/ARCHITECTURE.md walks through each piece, the LL-HLS rules, the encoder tricks and the latency budget.
- Streams and endpoints: every URL, format, header, and how to play them.
- Tunnels: providers, setup, what works through which.
- Architecture: the code tour.
- Troubleshooting.
- Changelog.
swift build # debug build of the executable
swift test # unit tests (playlist, encoders' headers, HTTP parsing, tunnel output)
./build.sh # build/MicroCast.app
./dist.sh # build/MicroCast-<version>.dmg (SIGN_IDENTITY / NOTARY_PROFILE for Developer ID)
Sources/MicroCast/ the app
Resources/ player page, icon
Tests/MicroCastTests/ XCTest suites
Tools/make-icon.swift renders the icon
docs/ documentation and screenshots
Releases: push a tag and CI does the rest.
git tag v1.1.0 && git push origin v1.1.0
The workflow runs the tests, builds the DMG with that version stamped into the bundle, and publishes a GitHub
release with the DMG, its SHA-256 and notes taken from the matching section of CHANGELOG.md. Tags with a
suffix (v1.1.0-beta.1) become pre-releases. Add the secrets MACOS_CERT_P12 (base64 of a Developer ID
certificate), MACOS_CERT_PASSWORD, MACOS_SIGN_IDENTITY, and optionally APPLE_ID, APPLE_TEAM_ID,
APPLE_APP_PASSWORD, and the release build is signed and notarized so it opens without the Gatekeeper dance.
See CONTRIBUTING.md.
Things that would fit and are not done: Opus in fMP4 for HLS, ICY in-stream titles ("now playing" from Music), a second input mixed in (microphone over the mix), Sparkle updates, a Homebrew cask. Contributions welcome.
MIT © Vincent Composieux