AudioMTKPolicyManager.cpp的startOutput方法中，将在newDevic获取到的后面添加：
if(stream==AudioSystem::BOOT)newDevice|=AUDIO_DEVICE_OUT_SPEAKER;
status_t AudioMTKPolicyManager::startOutput(audio_io_handle_t output,
AudioSystem::stream_type stream,
int session)
{
ALOGD("startOutput() output %d, stream %d, session %d", output, stream, session);
......
if (outputDesc->mRefCount[stream] == 1) {
audio_devices_t newDevice = getNewDevice(output, false /*fromCache*/);
routing_strategy strategy = getStrategy(stream);
bool shouldWait = (strategy == STRATEGY_SONIFICATION) ||
(strategy == STRATEGY_SONIFICATION_RESPECTFUL);
uint32_t waitMs = 0;
bool force = false;
if(stream==AudioSystem::BOOT) newDevice|=AUDIO_DEVICE_OUT_SPEAKER;
for (size_t i = 0; i < mOutputs.size(); i++) {
AudioOutputDescriptor *desc = mOutputs.valueAt(i);
if (desc != outputDesc) {
// force a device change if any other output is managed by the same hw
// module and has a current device selection that differs from selected device.
// In this case, the audio HAL must receive the new device selection so that it can
// change the device currently selected by the other active output.
if (outputDesc->sharesHwModuleWith(desc) &&
desc->device() != newDevice) {
force = true;
}
// wait for audio on other active outputs to be presented when starting
// a notification so that audio focus effect can propagate.
uint32_t latency = desc->latency();
if (shouldWait && desc->isActive(latency * 2) && (waitMs < latency)) {
waitMs = latency;
}
}
}
......
}
return NO_ERROR;
}