Andorid 13 修改默认音量区间、默认音量值

Andorid 13 默认音量区间是 [0,15] ，默认音量 5。

需求是：音量区间为 [0,100] ，默认音量 30 。

找到对应产品的 device.mk ，添加如下

#default volume
PRODUCT_PROPERTY_OVERRIDES += \
   ro.config.media_vol_steps=100 \
   ro.config.media_vol_default=30
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意思是音量区间为 [0,100] ，默认音量 30 。

这两个属性可以追溯到 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            // configured by config_audio_ring_vol_steps
        15, // STREAM_MUSIC
        7,  // STREAM_ALARM
        7,  // STREAM_NOTIFICATION    // configured by config_audio_notif_vol_steps
        15, // STREAM_BLUETOOTH_SCO
        7,  // STREAM_SYSTEM_ENFORCED
        15, // STREAM_DTMF
        15, // STREAM_TTS
        15, // STREAM_ACCESSIBILITY
        15  // STREAM_ASSISTANT
    };

    /** Minimum volume index values for audio streams */
    protected static int[] MIN_STREAM_VOLUME = new int[] {
        1,  // STREAM_VOICE_CALL
        0,  // STREAM_SYSTEM
        0,  // STREAM_RING
        0,  // STREAM_MUSIC
        1,  // STREAM_ALARM
        0,  // STREAM_NOTIFICATION
        0,  // STREAM_BLUETOOTH_SCO
        0,  // STREAM_SYSTEM_ENFORCED
        0,  // STREAM_DTMF
        0,  // STREAM_TTS
        1,  // STREAM_ACCESSIBILITY
        0   // STREAM_ASSISTANT
    };


    // ...


        int maxMusicVolume = SystemProperties.getInt("ro.config.media_vol_steps", -1);
        if (maxMusicVolume != -1) {
            MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] = maxMusicVolume;
        }

        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;
            }
        }
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默认音量值定义在 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           // configured in AudioService by config_audio_notif_vol_default
        5, // STREAM_MUSIC
        6,  // STREAM_ALARM
        5,  // STREAM_NOTIFICATION   // configured in AudioService by config_audio_ring_vol_default
        7,  // STREAM_BLUETOOTH_SCO
        7,  // STREAM_SYSTEM_ENFORCED
        5, // STREAM_DTMF
        5, // STREAM_TTS
        5, // STREAM_ACCESSIBILITY
        5, // STREAM_ASSISTANT
    };
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可以看到，

• 最大音量是读取 ro.config.media_vol_steps 属性的值，未赋值就用 MAX_STREAM_VOLUME 数组里定义的，数组里的值按照声音通道区分。
• 默认音量是读取 ro.config.media_vol_default 属性的值，未赋值就用 DEFAULT_STREAM_VOLUME 数组里定义的，数组里的值按照声音通道区分。