feat: AudioManager.getSystemVolume() — synchronous system volume read

[lpmv]

Why

AudioManager can observe volume changes (observeVolumeChanges + the volumeChange event) but has no way to read the volume before any change has fired. An app that wants to warn "your volume is at the floor" at the moment the user presses play cannot know the current level until the user happens to press a volume button.

What

A synchronous read on the exact scale the volumeChange event already reports:

const volume = AudioManager.getSystemVolume(); // 0..1

• iOS: AVAudioSession.outputVolume
• Android: STREAM_MUSIC volume as a fraction of its maximum

Exposed via the TurboModule spec mirroring getDevicePreferredSampleRate's blocking-synchronous form; the iOS implementation delegates to AudioSessionManager like its siblings.

Notes

The JSDoc carries the honest iOS caveat: a cold read before any volume-change event can report a stale or zero value on some iOS versions (KVO on outputVolume is the trustworthy stream once it speaks); callers who care can treat an exact 0.0 cold read as suspect. That caveat exists with or without this API — this just gives apps the same read the KVO baseline uses.

[mdydek]

@lpmv can you also please update the documentation? https://github.com/software-mansion/react-native-audio-api/blob/main/packages/audiodocs/docs/system/audio-manager.mdx

[closetcaiman]

Please update the documentation.

[github-actions]

WPT non-regression comparison

PASS — no regressions · 3 improved section(s) · overall 2574 → 2585 (+11)

Spec section	Base pass	Head pass	Delta
AnalyserNode	137	138	+1
AudioParam	597	599	+2
WaveShaperNode	67	75	+8

Unchanged sections (25)

Spec section	Base pass	Head pass	Delta
Processing model	0	0	0
Other	52	52	0
AudioBuffer	140	140	0
AudioBufferSourceNode	208	208	0
AudioContext	54	54	0
AudioNode	261	261	0
BiquadFilterNode	232	232	0
ChannelMergerNode	30	30	0
ChannelSplitterNode	7	7	0
ConstantSourceNode	59	59	0
ConvolverNode	170	170	0
DelayNode	104	104	0
DestinationNode	0	0	0
DynamicsCompressorNode	4	4	0
GainNode	15	15	0
IIRFilterNode	87	87	0
MediaElementAudioSourceNode	0	0	0
MediaStreamAudioDestinationNode	1	1	0
MediaStreamAudioSourceNode	0	0	0
OfflineAudioContext	35	35	0
OscillatorNode	104	104	0
PannerNode	75	75	0
PeriodicWave	33	33	0
ScriptProcessorNode	0	0	0
StereoPannerNode	102	102	0

_{Baseline: b0c368490c35169977de71991b0e882672684c2f · Candidate: d2e533b99cdb308bd0f6051ae493f74c5ef1e3d2}

_{Workflow run · this comment is updated on every push.}