Function start_recording 

pub fn start_recording(world: &mut World, max_seconds: f32) -> RecordingHandle

Start recording everything world fills, for at most max_seconds.

The recorder runs after every other OnAudioFill source and keeps the mix after the world’s GlobalAudioGain and the unit-range clamp, so the result is what the output stream receives. Because a source is handed the buffer before the dispatcher scales it, the recorder applies the gain itself; that is the one step it repeats rather than observes. No call fills the world: whichever driver usually does (the audio thread, dispatch_audio_fill directly, a stepped world) keeps doing it, and the recording grows as it goes.