backgroundmusic

Background Music is an open-source macOS audio utility (GPLv2 or later) that installs a virtual audio device and provides three main capabilities. Auto-pause music: when a second audio source starts playing, Background Music pauses your music player, and unpauses it when that source stops. Supported players include iTunes, Spotify, VLC, VOX, Decibel, Hermes, Swinsian and GPMDP; adding new players is described as usually straightforward, though players without AppleScript support for isPlaying/isPaused/play/pause events may require more work. Application volume: each running application gets its own volume slider, and quiet applications can be boosted above their normal maximum. The README notes that setting an app above 50% can cause clipping, and that only 2-channel (stereo) output devices are currently supported. Recording system audio: with Background Music running, QuickTime Player can select the Background Music device as input for audio, screen or movie recordings. Combining it with a microphone is possible through an aggregate device created in Audio MIDI Setup. The project requires macOS 10.13+ and is distributed as a signed pkg (version 0.5.0 in the README) or via Homebrew cask `background-music`. It sets itself as the default output device on launch and restores the previous device on quit; no restart is required to install. Building from source needs Xcode 10 or higher and a provided build_and_install.sh script, which restarts coreaudiod. Uninstall is handled by uninstall.sh inside the app bundle. The README documents troubleshooting steps: resetting the default output device if audio stops after a crash, granting microphone permission (needed because the virtual input device is treated as a microphone, though the app does not listen to the mic), checking "More Apps" entries for helper processes, and known conflicts such as VLC or Skype pausing other players, a Chrome device-switching bug, and headphone plug/unplug silence. Related projects listed include Soundflower, WavTap, eqMac, BlackHole and others.