对 AudioManager.STREAM_VOICE_CALL 音频流类型进行分析
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
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;
...
}
}
可以， voice call的音频策略是 phone
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;
...
switch (strategy) {
...
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;
}