FDSoundActivatedRecorder is a Swift library for iOS that implements sound-activated audio recording. It automatically starts recording when sound exceeds a dynamic threshold and stops when silence is detected, saving the output as an m4a file with fade-in/fade-out to prevent clicks. The core logic uses a moving average of audio power levels to dynamically adjust trigger thresholds, making it robust to varying noise environments. Built with modern Swift concurrency (actor) for thread safety, it provides a delegate protocol for callbacks and metering updates. The library is self-contained, depends only on standard iOS frameworks, and includes an example app demonstrating integration via SwiftUI.