AOSP ~ modify default volume

frameworks/base/media/java/android/media/AudioSystem.java

    /** @hide */
    public static int[] DEFAULT_STREAM_VOLUME = new int[] {
    
        4,  // STREAM_VOICE_CALL
        7,  // STREAM_SYSTEM
        5,  // STREAM_RING
        5, // STREAM_MUSIC
        6,  // STREAM_ALARM
        5,  // STREAM_NOTIFICATION
        7,  // STREAM_BLUETOOTH_SCO
        7,  // STREAM_SYSTEM_ENFORCED
        5, // STREAM_DTMF
        5, // STREAM_TTS
        5, // STREAM_ACCESSIBILITY
        5, // STREAM_ASSISTANT
    };

frameworks/base/services/core/java/com/android/server/audio/AudioService.java

   /** Maximum volume index values for audio streams */
    protected static int[] MAX_STREAM_VOLUME = new int[] {
    
        5,  // STREAM_VOICE_CALL
        7,  // STREAM_SYSTEM
        7,  // STREAM_RING
        15, // STREAM_MUSIC
        7,  // STREAM_ALARM
        7,  // STREAM_NOTIFICATION
        15, // STREAM_BLUETOOTH_SCO
        7,  // STREAM_SYSTEM_ENFORCED
        15, // STREAM_DTMF
        15, // STREAM_TTS
        15, // STREAM_ACCESSIBILITY
        15  // STREAM_ASSISTANT
    };

DEFAULT_STREAM_VOLUME
Default volume , The value does not represent the specific volume , It's how much

MAX_STREAM_VOLUME
Maximum volume

ro.config.media_vol_default
If this value is defined , The default volume value will be set to the size of the attribute value . If the attribute value is not defined , The default volume value is forced to be set to the maximum volume value 1/4（ Mobile phone mode ） perhaps 1/3（ Other modes ）.

therefore , Want to change the default media Volume size , There are two ways to modify

• One way is to define ro.config.media_vol_default System property values for , This method does not need to modify the source file , Just add a sentence to the configuration file
• The other way is , take AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] Forcibly assign the value to the volume you want to set

        int maxMusicVolume = SystemProperties.getInt("ro.config.media_vol_steps", -1);
        if (maxMusicVolume != -1) {
    
            MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] = maxMusicVolume;
        }
        if(isBox()){
    
            mFixedVolumeDevices.clear();
        }
        int defaultMusicVolume = SystemProperties.getInt("ro.config.media_vol_default", -1);
        if (defaultMusicVolume != -1 &&
                defaultMusicVolume <= MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] &&
                defaultMusicVolume >= MIN_STREAM_VOLUME[AudioSystem.STREAM_MUSIC]) {
    
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] = defaultMusicVolume;
        } else {
    
            if (isPlatformTelevision()) {
    
                AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] =
                        MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] / 4;
            } else {
    
                AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] =
                        MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] / 3;
            }
        }