音频流, 音频策略, 输出设备之间的关系

只针对 AudioManager.STREAM_VOICE_CALL 音频流类型进行分析

涉及到的类:

hardware/libhardware_legacy/audio/AudioPolicyManagerBase.cpp

frameworks/base/media/java/android/media/AudioManager.java

frameworks/base/media/java/android/media/AudioService.java

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

涉及到的方法及执行顺序:

AudioPolicyManagerBase.getStrategy(AudioSystem::stream_type stream);

AudioPolicyManagerBase.getDeviceForStrategy(routing_strategy strategy, bool fromCache);

一. 通过音频流的类型获取对应的音频策略

AudioPolicyManagerBase.cpp:

AudioPolicyManagerBase::routing_strategy AudioPolicyManagerBase::getStrategy(AudioSystem::stream_type stream) {

// stream to strategy mapping

switch (stream) {

case AudioSystem::VOICE_CALL:

case AudioSystem::BLUETOOTH_SCO:

return STRATEGY_PHONE;

...

}

}

二. 通过音频策略获取到对应的输出设备

AudioPolicyManagerBase.cpp:

audio_devices_t AudioPolicyManagerBase::getDeviceForStrategy(routing_strategy strategy, bool fromCache) {

uint32_t device = AUDIO_DEVICE_NONE;

... // 省略

switch (strategy) {

... // 省略

case STRATEGY_PHONE:

// for phone strategy, we first consider the forced use and then the available devices by order

// of priority

switch (mForceUse[AudioSystem::FOR_COMMUNICATION]) { // 判断是否有设置在通讯过程中, 强制使用某种输出设备

case AudioSystem::FORCE_BT_SCO: // 强制使用蓝牙, 作为输出设备

if (!isInCall() || strategy != STRATEGY_DTMF) {

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT;

if (device) break;

}

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_SCO;

if (device) break;

// if SCO device is requested but no SCO device is available, fall back to default case

// FALL THROUGH

default: // FORCE_NONE 没有设置通讯过程中, 强制使用某种输出设备

// when not in a phone call, phone strategy should route STREAM_VOICE_CALL to A2DP

if (mHasA2dp && !isInCall() &&

(mForceUse[AudioSystem::FOR_MEDIA] != AudioSystem::FORCE_NO_BT_A2DP) &&

(getA2dpOutput() != 0) && !mA2dpSuspended) {

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES;

if (device) break;

}

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_WIRED_HEADPHONE;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_WIRED_HEADSET;

if (device) break;

if (mPhoneState != AudioSystem::MODE_IN_CALL) {

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_USB_ACCESSORY;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_USB_DEVICE;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_AUX_DIGITAL;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET;

if (device) break;

}

// 没有设置通讯过程中, 音频的输出设备, 则默认使用听筒作为输出设备

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_EARPIECE;

if (device) break;

device = mDefaultOutputDevice;

if (device == AUDIO_DEVICE_NONE) {

ALOGE("getDeviceForStrategy() no device found for STRATEGY_PHONE");

}

break;

case AudioSystem::FORCE_SPEAKER: // 强制使用扬声器, 作为输出设备

// when not in a phone call, phone strategy should route STREAM_VOICE_CALL to

// A2DP speaker when forcing to speaker output

if (mHasA2dp && !isInCall() &&

(mForceUse[AudioSystem::FOR_MEDIA] != AudioSystem::FORCE_NO_BT_A2DP) &&

(getA2dpOutput() != 0) && !mA2dpSuspended) {

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER;

if (device) break;

}

if (mPhoneState != AudioSystem::MODE_IN_CALL) {

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_USB_ACCESSORY;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_USB_DEVICE;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_AUX_DIGITAL;

if (device) break;

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET;

if (device) break;

}

device = mAvailableOutputDevices & AUDIO_DEVICE_OUT_SPEAKER;

if (device) break;

device = mDefaultOutputDevice;

if (device == AUDIO_DEVICE_NONE) {

ALOGE("getDeviceForStrategy() no device found for STRATEGY_PHONE, FORCE_SPEAKER");

}

break;

}

break;

// 关于上面default位置的问题, 如果每个case选择(包括default)最终都有break语句, 则default的位置不影响执行顺序

// 当每个case选择(包括default)不一定有break语句时, 如果输入不满足其他选择, 最终执行default. 程序会从default处从上向下执行, 直到遇到break语句停止

// 此处的default位置并不影响执行顺序

... // 省略

}

return device;

}

三. 音频流, 音频策略, 输出设备之间的关系

音频的流类型决定音频的策略, 音频的策略决定输出设备. 但是最终的输出设备的确定, 受强制设置输出设备影响.

四. 分析AudioManager.setSpeakerphoneOn(boolean on)方法, 查看强制设置对音频输出设备选择的影响

涉及到的类及方法:

1. AudioManager.setSpeakerphoneOn(boolean on);

2. AudioService.setSpeakerphoneOn(boolean on);

3. AudioService.AudioHandler.setForceUse(int usage, int config);

4. AudioSystem.setForceUse(int usage, int config);

5. AudioPolicyManagerBase.setForceUse(AudioSystem::force_use usage, AudioSystem::forced_config config);

4.1. AudioManager.java:

public void setSpeakerphoneOn(boolean on){

IAudioService service = getService();

service.setSpeakerphoneOn(on);

}

4.2. AudioService.java:

public void setSpeakerphoneOn(boolean on){

if (on) {

if (mForcedUseForComm == AudioSystem.FORCE_BT_SCO) {

sendMsg(mAudioHandler, MSG_SET_FORCE_USE, SENDMSG_QUEUE,

AudioSystem.FOR_RECORD, AudioSystem.FORCE_NONE, null, 0);

}

mForcedUseForComm = AudioSystem.FORCE_SPEAKER;

} else if (mForcedUseForComm == AudioSystem.FORCE_SPEAKER){

mForcedUseForComm = AudioSystem.FORCE_NONE;

}

// 从此处可以看到 setSpeakerphoneOn(boolean on) 只针对 AudioSystem.FOR_COMMUNICATION 有效

// 而 AudioSystem.FOR_COMMUNICATION 最终影响到的是输出设备的选择

sendMsg(mAudioHandler, MSG_SET_FORCE_USE, SENDMSG_QUEUE,

AudioSystem.FOR_COMMUNICATION, mForcedUseForComm, null, 0);

}

private class AudioHandler extends Handler {

@Override

public void handleMessage(Message msg) {

switch (msg.what) {

case MSG_SET_FORCE_USE:

case MSG_SET_FORCE_BT_A2DP_USE:

setForceUse(msg.arg1, msg.arg2);

break;

}

}

private void setForceUse(int usage, int config) {

AudioSystem.setForceUse(usage, config);

}

}

4.3. AudioSystem.java:

public static native int setForceUse(int usage, int config);

4.4. AudioPolicyManagerBase.cpp:

void AudioPolicyManagerBase::setForceUse(AudioSystem::force_use usage, AudioSystem::forced_config config) {

bool forceVolumeReeval = false;

switch(usage) {

case AudioSystem::FOR_COMMUNICATION:

if (config != AudioSystem::FORCE_SPEAKER && config != AudioSystem::FORCE_BT_SCO &&

config != AudioSystem::FORCE_NONE) {

ALOGW("setForceUse() invalid config %d for FOR_COMMUNICATION", config);

return;

}

forceVolumeReeval = true;

// 保存设置到数组中, 最终在 getDeviceForStrategy(routing_strategy strategy, bool fromCache) 中被调用

mForceUse[usage] = config;

break;

... // 省略

}

... // 省略

}

原文出处：https://www.cnblogs.com/firmly-believe/p/10991077.html