stream volume in SoundPool vs volume in AudioManager

I am so confused...

SoundPool.play(int soundID, float leftVolume, float rightVolume, int priority, int loop, float rate)

volume here is from 0.0 to 1.0

Tutorials I've seen recommend to calculate stream volume as:

AudioManager mgr = (AudioManager) getContext().getSystemService(Context.AUDIO_SERVICE);

int streamVolume = mgr.getStreamVolume(AudioManager.STREAM_MUSIC);

streamVolume = streamVolume / AudioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);

mSoundPool.play(mSoundPoolMap.get(index), streamVolume, streamVolume, 1, 0, 1f);

which makes sense.

I would assume that this volume would override 开发者_运维百科global media volume set by user in phone and I can change volume for my app independently by changing stream volume in soundPool.

But in reality it works like multiplier - if I set 0.5 for volume in soundpool, the actual volume will be always half of the global one. Very easy to reproduce:

1. set global media volume in phone settings to max
2. set volume in activity using soundpool.play to 0.5 - play sound
3. set volume in soundpool.play to 1 - play sound, it will be two times louder

Can somebody explain why it works like that? is volume passed to SoundPool.play method really a multiplier to the global volume?

Yes, the volume parameters are with respect to the global volume. If you want to play a sound at the current volume setting just pass "1" as the volume.