setVolume method
Sets the soft volume in percent: 100 plays at unity and values above it amplify. mpv's scale is cubic: 130 is about +7 dB, 1000 is +60 dB.
Takes 0 to 1000. Throws RangeError when negative, and
MpvCommandException above 1000, which mpv refuses.
PlayerSettings.volumeMax does not cap this call: it bounds mpv's
relative steps (add, cycle) only. Clamp a slider to it yourself.
Implementation
Future<void> setVolume(double volume) async {
_checkRange(volume, 0, double.maxFinite, 'volume');
await _gate();
final value = canonicalFloat(volume);
await _calls.prop('volume', value.toString());
_updateField((s) => s.copyWith(volume: value), _reactives.volume, value);
}