[RK3288][Android6.0] Audio的音量计算过程小结

最新推荐文章于 2023-03-15 17:14:11 发布

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最新推荐文章于 2023-03-15 17:14:11 发布 · 5.3k 阅读

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#audio #音量计算

本文详细介绍了在Android 6.0系统中，针对RK3288平台的音频处理，特别是音量计算的过程。通过分析`getVolumeCurvePoint`函数，揭示了AudioService如何在创建流状态时设定音量曲线，从而控制设备的音量变化。

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Platform: Rockchip
OS: Android 6.0
Kernel: 3.10.92

AudioPolicyManager::checkAndSetVolume -> AudioPolicyManager.cpp
AudioPolicyManager::computeVolume ->
mEngine->volIndexToDb ->
Engine::volIndexToDb -> frameworks/av/services/audiopolicy/enginedefault/Engine.cpp
Gains::volIndexToDb -> Gains.cpp
outputDesc->setVolume ->
SwAudioOutputDescriptor::setVolume ->
Volume::DbToAmpl

index -> db:
volIndexToDb()会将index转换成db.

float Gains::volIndexToDb(Volume::device_category deviceCategory,
                          const StreamDescriptor& streamDesc,
                          int indexInUi)
{
    //对应的是Gains::sVolumeProfiles列表，假设本例是改变music stream的音量，用的是speaker，
    //那么就是Gains::sSpeakerMediaVolumeCurve,后面会解释它的由来，见说明一
    //Gains::sSpeakerMediaVolumeCurve[Volume::VOLCNT] = {
    //{1, -56.0f}, {20, -34.0f}, {60, -11.0f}, {100, 0.0f}
    //};

    const VolumeCurvePoint *curve = streamDesc.getVolumeCurvePoint(deviceCategory);

    // the volume index in the UI is relative to the min and max volume indices for this stream type
    //nbssteps = 1 + 100 - 1