App Capture uses macOS ScreenCaptureKit to tap the audio output of a specific running application and route it directly into the SignalCaster encoder. It’s perfect for streaming audio from a DJ app, a DAW, a media player, or any other software that produces sound — without routing cables or setting up virtual audio devices.
App Capture requires macOS 14.4 or later. On older versions of macOS the option will still appear in the Audio Source selector but won’t function. The first time you use App Capture, macOS will prompt you to grant Screen Recording permission to SignalCaster — you need to allow this even though no screen video is captured.
In the Settings drawer, set Audio Source to App Capture. A second popup appears immediately below, listing every audio-producing application currently running on your Mac. Select the app whose audio you want to capture.
If your target app isn’t in the list, make sure it’s running and producing audio. Some apps don’t register with ScreenCaptureKit until they actually play sound. Try playing something in the app and then checking the list again.
Pick a different app from the app picker popup at any time — even while streaming. SignalCaster stops capturing from the old app and immediately starts capturing from the new one. There will be a very brief audio gap during the switch, typically less than a second.
ScreenCaptureKit delivers audio at 48,000 Hz. SignalCaster uses this sample rate directly with most streaming targets. For Facebook Live, which requires 44,100 Hz, the audio is automatically resampled before encoding. The Activity Log notes when resampling is active.
SignalCaster has no way to know what the captured application is currently playing, so the dashboard Now Playing label stays blank in App Capture mode. For Icecast streams, the metadata won’t update with track names. If you need now-playing information on your stream, the Local Player or TCP Input (AutoCast) sources are better choices.
If App Capture suddenly stops working (VU meters go flat, Activity Log shows capture errors), check System Settings › Privacy & Security › Screen Recording and confirm that SignalCaster still has permission. macOS occasionally revokes this after system updates.