Android Audio代码分析26 - Audio Strategy

在看示例代码 testPlaybackHeadPositionIncrease 的时候，我们对 play 函数进行了研究。
不过，当时对 Android 中声音竞争策略相关的内容，并没有详细分析。
今天就以 AudioTrack 的播放为引子，来仔细看看 Anroid 中各种声音是以什么样的策略来竞争的。


从 Java 侧类 AudioTrack 的 play 函数到函数 AudioFlinger::PlaybackThread::Track::start 之间的调用关系就不再叙述了。
在看示例代码 testPlaybackHeadPositionIncrease 的时候已经说明过了。
今天就从函数 AudioFlinger::PlaybackThread::Track::start 开始分析。


*****************************************源码*************************************************
status_t AudioFlinger::PlaybackThread::Track::start() { status_t status = NO_ERROR; LOGV("start(%d), calling thread %d session %d", mName, IPCThreadState::self()->getCallingPid(), mSessionId); sp<ThreadBase> thread = mThread.promote(); if (thread != 0) { Mutex::Autolock _l(thread->mLock); int state = mState; // here the track could be either new, or restarted // in both cases "unstop" the track if (mState == PAUSED) { mState = TrackBase::RESUMING; LOGV("PAUSED => RESUMING (%d) on thread %p", mName, this); } else { mState = TrackBase::ACTIVE; LOGV("? => ACTIVE (%d) on thread %p", mName, this); } if (!isOutputTrack() && state != ACTIVE && state != RESUMING) { thread->mLock.unlock(); status = AudioSystem::startOutput(thread->id(), (AudioSystem::stream_type)mStreamType, mSessionId); thread->mLock.lock(); } if (status == NO_ERROR) { PlaybackThread *playbackThread = (PlaybackThread *)thread.get(); playbackThread->addTrack_l(this); } else { mState = state; } } else { status = BAD_VALUE; } return status; }
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源码路径：
frameworks\base\services\AudioFlinger.cpp


#######################说明################################
status_t AudioFlinger::PlaybackThread::Track::start() { status_t status = NO_ERROR; LOGV("start(%d), calling thread %d session %d", mName, IPCThreadState::self()->getCallingPid(), mSessionId); sp<ThreadBase> thread = mThread.promote(); if (thread != 0) { Mutex::Autolock _l(thread->mLock); int state = mState; // here the track could be either new, or restarted // in both cases "unstop" the track if (mState == PAUSED) { mState = TrackBase::RESUMING; LOGV("PAUSED => RESUMING (%d) on thread %p", mName, this); } else { mState = TrackBase::ACTIVE; LOGV("? => ACTIVE (%d) on thread %p", mName, this); } if (!isOutputTrack() && state != ACTIVE && state != RESUMING) { thread->mLock.unlock(); status = AudioSystem::startOutput(thread->id(), (AudioSystem::stream_type)mStreamType, mSessionId); // ++++++++++++++++++++++++++++AudioSystem::startOutput++++++++++++++++++++++++++++++++++++ // 从函数 AudioFlinger::PlaybackThread::Track::start 进入： status_t AudioSystem::startOutput(audio_io_handle_t output, AudioSystem::stream_type stream, int session) { const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service(); if (aps == 0) return PERMISSION_DENIED; return aps->startOutput(output, stream, session); // +++++++++++++++++++++++++++++AudioPolicyService::startOutput+++++++++++++++++++++++++++++++++++ // 从函数 AudioSystem::startOutput 进入： status_t AudioPolicyService::startOutput(audio_io_handle_t output, AudioSystem::stream_type stream, int session) { if (mpPolicyManager == NULL) { return NO_INIT; } LOGV("startOutput() tid %d", gettid()); Mutex::Autolock _l(mLock); return mpPolicyManager->startOutput(output, stream, session); // +++++++++++++++++++++++++++++AudioPolicyManagerBase::startOutput+++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyService::startOutput 进入： // 主要的处理是从这儿开始的 status_t AudioPolicyManagerBase::startOutput(audio_io_handle_t output, AudioSystem::stream_type stream, int session) { LOGV("startOutput() output %d, stream %d, session %d", output, stream, session); ssize_t index = mOutputs.indexOfKey(output); if (index < 0) { LOGW("startOutput() unknow output %d", output); return BAD_VALUE; } AudioOutputDescriptor *outputDesc = mOutputs.valueAt(index); // 函数 getStrategy 就是根据 stream type 返回特定的 strategy routing_strategy strategy = getStrategy((AudioSystem::stream_type)stream); // ++++++++++++++++++++++++++++AudioPolicyManagerBase::getStrategy++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::startOutput 进入： // 本来不打算列出该函数，不过，看到后面关于 strategy 优先级的时候，发现需要知道每种策略分别是用来干吗的。 // 所以首先要知道策略对应的 stream type ， AudioPolicyManagerBase::routing_strategy AudioPolicyManagerBase::getStrategy( AudioSystem::stream_type stream) { // stream to strategy mapping switch (stream) { case AudioSystem::VOICE_CALL: // 电话来了 case AudioSystem::BLUETOOTH_SCO: // 蓝牙耳机接通了 return STRATEGY_PHONE; case AudioSystem::RING: // 铃声响了 case AudioSystem::NOTIFICATION: // 通知，例如界面中最上面一栏中有消息了 case AudioSystem::ALARM: // 警告，电池没电时的警告？ case AudioSystem::ENFORCED_AUDIBLE: return STRATEGY_SONIFICATION; case AudioSystem::DTMF: // 可参考链接：http://baike.baidu.com/view/171916.htm return STRATEGY_DTMF; default: LOGE("unknown stream type"); case AudioSystem::SYSTEM: // 系统声音采用 media strategy, 例如，如果正在播放音乐的时候按键， // mute 掉音乐，并切换 output 的话，将导致 很差的用户体验。 // 其中可以得到以下信息： // 1、按键声音属于 system stream type 。 // 2、策略的改变将会导致 output 的切换 // 3、优先级高的策略 start 时会 mute 掉优先级低的策略 // NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs // while key clicks are played produces a poor result case AudioSystem::TTS: // TTS 就是 Text To Speech case AudioSystem::MUSIC: return STRATEGY_MEDIA; } } // 返回到函数 AudioPolicyManagerBase::startOutput // ----------------------------AudioPolicyManagerBase::getStrategy------------------------------------ #ifdef WITH_A2DP if (mA2dpOutput != 0 && !a2dpUsedForSonification() && strategy == STRATEGY_SONIFICATION) { setStrategyMute(STRATEGY_MEDIA, true, mA2dpOutput); } #endif // incremenent usage count for this stream on the requested output: // NOTE that the usage count is the same for duplicated output and hardware output which is // necassary for a correct control of hardware output routing by startOutput() and stopOutput() // 增加请求的 output 上该 stream 的使用计数 // 注意： duplicated output 和 hardware output 中的使用计数是相同的。 // 因为这对通过 startOutput() 函数和 stopOutput() 函数正确地控制 hardware output routing 是必要的。 outputDesc->changeRefCount(stream, 1); // ++++++++++++++++++++++++++++AudioPolicyManagerBase::AudioOutputDescriptor::changeRefCount++++++++++++++++++++++++++++++++++++ 从函数 AudioPolicyManagerBase::startOutput 进入： void AudioPolicyManagerBase::AudioOutputDescriptor::changeRefCount(AudioSystem::stream_type stream, int delta) { // forward usage count change to attached outputs // 如果是 duplicated 的，需要改变它所包含的两个 output 中的使用计数。 if (isDuplicated()) { mOutput1->changeRefCount(stream, delta); mOutput2->changeRefCount(stream, delta); } if ((delta + (int)mRefCount[stream]) < 0) { LOGW("changeRefCount() invalid delta %d for stream %d, refCount %d", delta, stream, mRefCount[stream]); mRefCount[stream] = 0; return; } mRefCount[stream] += delta; LOGV("changeRefCount() stream %d, count %d", stream, mRefCount[stream]); } // 返回到函数 AudioPolicyManagerBase::startOutput // ----------------------------AudioPolicyManagerBase::AudioOutputDescriptor::changeRefCount------------------------------------ setOutputDevice(output, getNewDevice(output)); // ++++++++++++++++++++++++++++AudioPolicyManagerBase::getNewDevice++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::startOutput 进入： uint32_t AudioPolicyManagerBase::getNewDevice(audio_io_handle_t output, bool fromCache) { uint32_t device = 0; AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output); // check the following by order of priority to request a routing change if necessary: // 1: we are in call or the strategy phone is active on the hardware output: // use device for strategy phone // 2: the strategy sonification is active on the hardware output: // use device for strategy sonification // 3: the strategy media is active on the hardware output: // use device for strategy media // 4: the strategy DTMF is active on the hardware output: // use device for strategy DTMF // 根据以下的优先级顺序，来检查必要的路线改变 // 1、如果来电话了，或者 hardware output 中的 strategy phone 是活动的， // 则使用 phone strategy 。 // 有两种情况会使用到 strategy phone ，来电话了和蓝牙耳机接通了。 // 2、如果 hardware output 中的 strategy sonification 是活动的， // 则使用 strategy sonification . // 有四种情况会使用 stratety sonification ，来电铃声，通知，警告， // 和是 ENFORCED_AUDIBLE stream 的时候。 // 3、如果 hardware output 中的 strategy media 是活动的， // 则使用 strategy media . // Media 播放， 系统声音和 TTS 会使用 media 策略。 // 4、如果 hardware output 中的 strategy DTMF 是活动的， // 则使用 strategy DTMF . // 在 stream type 是 DTMF 的时候会使用 DTMF 策略。 // 关于 DTMF 请参考 http://baike.baidu.com/view/171916.htm if (isInCall() || outputDesc->isUsedByStrategy(STRATEGY_PHONE)) { // bool isUsedByStrategy(routing_strategy strategy) { return (strategyRefCount(strategy) != 0);} // +++++++++++++++++++++++++++AudioPolicyManagerBase::AudioOutputDescriptor::strategyRefCount+++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::getNewDevice 进入： // 检查 output 中是否使用了指定的 strategy uint32_t AudioPolicyManagerBase::AudioOutputDescriptor::strategyRefCount(routing_strategy strategy) { uint32_t refCount = 0; for (int i = 0; i < (int)AudioSystem::NUM_STREAM_TYPES; i++) { if (getStrategy((AudioSystem::stream_type)i) == strategy) { refCount += mRefCount[i]; } } return refCount; } // 返回到函数 AudioPolicyManagerBase::getNewDevice // ---------------------------AudioPolicyManagerBase::AudioOutputDescriptor::strategyRefCount------------------------------------- device = getDeviceForStrategy(STRATEGY_PHONE, fromCache); } else if (outputDesc->isUsedByStrategy(STRATEGY_SONIFICATION)) { device = getDeviceForStrategy(STRATEGY_SONIFICATION, fromCache); } else if (outputDesc->isUsedByStrategy(STRATEGY_MEDIA)) { device = getDeviceForStrategy(STRATEGY_MEDIA, fromCache); } else if (outputDesc->isUsedByStrategy(STRATEGY_DTMF)) { device = getDeviceForStrategy(STRATEGY_DTMF, fromCache); } // ++++++++++++++++++++++++++++AudioPolicyManagerBase::isInCall++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::getNewDevice 进入： bool AudioPolicyManagerBase::isInCall() { // 函数 AudioPolicyManagerBase::setPhoneState 中会改变 mPhoneState 的值 // 调用关系：android_media_AudioSystem_setPhoneState // 调用 AudioSystem::setPhoneState // 调用 AudioPolicyService::setPhoneState // 调用 AudioPolicyManagerBase::setPhoneState return isStateInCall(mPhoneState); // ++++++++++++++++++++++++++++AudioPolicyManagerBase::isStateInCall++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::isInCall 进入： bool AudioPolicyManagerBase::isStateInCall(int state) { return ((state == AudioSystem::MODE_IN_CALL) || (state == AudioSystem::MODE_IN_COMMUNICATION)); // +++++++++++++++++++++++++++++audio_mode+++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::isStateInCall 进入： enum audio_mode { MODE_INVALID = -2, MODE_CURRENT = -1, MODE_NORMAL = 0, MODE_RINGTONE, MODE_IN_CALL, MODE_IN_COMMUNICATION, NUM_MODES // not a valid entry, denotes end-of-list }; // 返回到函数 AudioPolicyManagerBase::isStateInCall // -----------------------------audio_mode----------------------------------- } // 返回到函数 AudioPolicyManagerBase::isInCall // ----------------------------AudioPolicyManagerBase::isStateInCall------------------------------------ } // 返回到函数 AudioPolicyManagerBase::getNewDevice // ----------------------------AudioPolicyManagerBase::isInCall------------------------------------ // +++++++++++++++++++++++++++AudioPolicyManagerBase::getDeviceForStrategy+++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::getNewDevice 进入： uint32_t AudioPolicyManagerBase::getDeviceForStrategy(routing_strategy strategy, bool fromCache) { uint32_t device = 0; if (fromCache) { LOGV("getDeviceForStrategy() from cache strategy %d, device %x", strategy, mDeviceForStrategy[strategy]); return mDeviceForStrategy[strategy]; } switch (strategy) { case STRATEGY_DTMF: if (!isInCall()) { // 不是打电话过来或者在通话中的话，DTMF strategy 和 MEDIA strategy 规则一样 // when off call, DTMF strategy follows the same rules as MEDIA strategy device = getDeviceForStrategy(STRATEGY_MEDIA, false); break; } // 有电话打过来，或者在通话中的话， DTMF strategy 和 PHONE strategy 规则一致 // when in call, DTMF and PHONE strategies follow the same rules // FALL THROUGH case STRATEGY_PHONE: // 对于 PHONE strategy ， 首先判断是否强制要求使用了什么设备，然后再根据优先级顺序，寻找可用的 device // for phone strategy, we first consider the forced use and then the available devices by order // of priority switch (mForceUse[AudioSystem::FOR_COMMUNICATION]) { case AudioSystem::FORCE_BT_SCO: if (!isInCall() || strategy != STRATEGY_DTMF) { // 不是上述两种情况的话，肯定是outputDesc->isUsedByStrategy(STRATEGY_PHONE)作为条件走到这一步的 device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_CARKIT; if (device) break; } device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_HEADSET; if (device) break; device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO; if (device) break; // 如果请求了 SCO device ，但是没有 SCO device 可用，则进入 default case // if SCO device is requested but no SCO device is available, fall back to default case // FALL THROUGH default: // FORCE_NONE device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADPHONE; if (device) break; device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADSET; if (device) break; #ifdef WITH_A2DP // when not in a phone call, phone strategy should route STREAM_VOICE_CALL to A2DP if (!isInCall()) { device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP; if (device) break; device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES; if (device) break; } #endif device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_EARPIECE; if (device == 0) { LOGE("getDeviceForStrategy() earpiece device not found"); } break; case AudioSystem::FORCE_SPEAKER: if (!isInCall() || strategy != STRATEGY_DTMF) { device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_CARKIT; if (device) break; } #ifdef WITH_A2DP // when not in a phone call, phone strategy should route STREAM_VOICE_CALL to // A2DP speaker when forcing to speaker output if (!isInCall()) { device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER; if (device) break; } #endif device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER; if (device == 0) { LOGE("getDeviceForStrategy() speaker device not found"); } break; } break; case STRATEGY_SONIFICATION: // If incall, just select the STRATEGY_PHONE device: The rest of the behavior is handled by // handleIncallSonification(). if (isInCall()) { device = getDeviceForStrategy(STRATEGY_PHONE, false); break; } device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER; if (device == 0) { LOGE("getDeviceForStrategy() speaker device not found"); } // The second device used for sonification is the same as the device used by media strategy // FALL THROUGH case STRATEGY_MEDIA: { uint32_t device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_AUX_DIGITAL; if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HDMI; } if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADPHONE; } if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADSET; } #ifdef WITH_A2DP if (mA2dpOutput != 0) { if (strategy == STRATEGY_SONIFICATION && !a2dpUsedForSonification()) { break; } if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP; } if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES; } if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER; } } #endif if (device2 == 0) { device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER; } // device is DEVICE_OUT_SPEAKER if we come from case STRATEGY_SONIFICATION, 0 otherwise device |= device2; if (device == 0) { LOGE("getDeviceForStrategy() speaker device not found"); } } break; default: LOGW("getDeviceForStrategy() unknown strategy: %d", strategy); break; } LOGV("getDeviceForStrategy() strategy %d, device %x", strategy, device); return device; } // 返回到函数 AudioPolicyManagerBase::getNewDevice // ---------------------------AudioPolicyManagerBase::getDeviceForStrategy------------------------------------- LOGV("getNewDevice() selected device %x", device); return device; } // 返回到函数 AudioPolicyManagerBase::startOutput // ----------------------------AudioPolicyManagerBase::getNewDevice------------------------------------ // ++++++++++++++++++++++++++++AudioPolicyManagerBase::setOutputDevice++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::startOutput 进入 void AudioPolicyManagerBase::setOutputDevice(audio_io_handle_t output, uint32_t device, bool force, int delayMs) { LOGV("setOutputDevice() output %d device %x delayMs %d", output, device, delayMs); AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output); // 如果 output 是 duplicated 的，直接去处理其包含的两个 output if (outputDesc->isDuplicated()) { setOutputDevice(outputDesc->mOutput1->mId, device, force, delayMs); setOutputDevice(outputDesc->mOutput2->mId, device, force, delayMs); return; } #ifdef WITH_A2DP // filter devices according to output selected if (output == m A2dpOutput) { device &= AudioSystem::DEVICE_OUT_ALL_A2DP; } else { device &= ~AudioSystem::DEVICE_OUT_ALL_A2DP; } #endif uint32_t prevDevice = (uint32_t)outputDesc->device(); // Do not change the routing if: // - the requestede device is 0 // - the requested device is the same as current device and force is not specified. // Doing this check here allows the caller to call setOutputDevice() without conditions if ((device == 0 || device == prevDevice) && !force) { LOGV("setOutputDevice() setting same device %x or null device for output %d", device, output); return; } // 修改 output 中的 current device outputDesc->mDevice = device; // mute media streams if both speaker and headset are selected if (output == mHardwareOutput && AudioSystem::popCount(device) == 2) { setStrategyMute(STRATEGY_MEDIA, true, output); // ++++++++++++++++++++++++++AudioPolicyManagerBase::setStrategyMute++++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::setOutputDevice 进入 // mute 掉指定 strategy 对应的所有 stream void AudioPolicyManagerBase::setStrategyMute(routing_strategy strategy, bool on, audio_io_handle_t output, int delayMs) { LOGV("setStrategyMute() strategy %d, mute %d, output %d", strategy, on, output); for (int stream = 0; stream < AudioSystem::NUM_STREAM_TYPES; stream++) { if (getStrategy((AudioSystem::stream_type)stream) == strategy) { setStreamMute(stream, on, output, delayMs); // +++++++++++++++++++++++++++AudioPolicyManagerBase::setStreamMute+++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::setStrategyMute 进入 void AudioPolicyManagerBase::setStreamMute(int stream, bool on, audio_io_handle_t output, int delayMs) { StreamDescriptor &streamDesc = mStreams[stream]; AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output); LOGV("setStreamMute() stream %d, mute %d, output %d, mMuteCount %d", stream, on, output, outputDesc->mMuteCount[stream]); if (on) { if (outputDesc->mMuteCount[stream] == 0) { // 如果该 stream 还没有 mute 过，则对其进行 mute if (streamDesc.mCanBeMuted) { // mute 其实就是将 stream 的音量设置为 0 // checkAndSetVolume 函数在此处就先不看了，等到下面看音量设置的时候在分析 checkAndSetVolume(stream, 0, output, outputDesc->device(), delayMs); } } // increment mMuteCount after calling checkAndSetVolume() so that volume change is not ignored // 将 mute 计数加1，以防止声音改变被忽略 outputDesc->mMuteCount[stream]++; } else { if (outputDesc->mMuteCount[stream] == 0) { // 如果 mute 计数为0，不进行任何操作 LOGW("setStreamMute() unmuting non muted stream!"); return; } if (--outputDesc->mMuteCount[stream] == 0) { // mute 计数减1，若 mute 计数变为0，则将 stream 变为 mute off // 也就是恢复 stream 的音量 checkAndSetVolume(stream, streamDesc.mIndexCur, output, outputDesc->device(), delayMs); } } } // 返回到函数 AudioPolicyManagerBase::setStrategyMute // ---------------------------AudioPolicyManagerBase::setStreamMute------------------------------------- } } } // 返回到函数 AudioPolicyManagerBase::setOutputDevice // --------------------------AudioPolicyManagerBase::setStrategyMute-------------------------------------- // wait for the PCM output buffers to empty before proceeding with the rest of the command usleep(outputDesc->mLatency*2*1000); } // do the routing AudioParameter param = AudioParameter(); param.addInt(String8(AudioParameter::keyRouting), (int)device); // 调用的其实是函数 AudioPolicyService::setParameters // 会通过函数 AudioPolicyService::AudioCommandThread::parametersCommand 向 AudioCommandThread 的 command list // 添加一个 command // AudioPolicyService::AudioCommandThread::threadLoop 函数中会处理 command list 中的 command // 对于 SET_PARAMETERS command ，最终调用了函数 AudioSystem::setParameters // 调用了 AudioFlinger::setParameters 函数 // 调用了 AudioFlinger::ThreadBase::setParameters 函数添加成员到 mNewParameters // 函数 AudioFlinger::MixerThread::checkForNewParameters_l 中会处理 mNewParameters 中的参数 // 函数 AudioFlinger::MixerThread::threadLoop 会调用函数 AudioFlinger::MixerThread::checkForNewParameters_l mpClientInterface->setParameters(mHardwareOutput, param.toString(), delayMs); // update stream volumes according to new device applyStreamVolumes(output, device, delayMs); // +++++++++++++++++++++++++AudioPolicyManagerBase::applyStreamVolumes+++++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::setOutputDevice 进入： void AudioPolicyManagerBase::applyStreamVolumes(audio_io_handle_t output, uint32_t device, int delayMs) { LOGV("applyStreamVolumes() for output %d and device %x", output, device); for (int stream = 0; stream < AudioSystem::NUM_STREAM_TYPES; stream++) { checkAndSetVolume(stream, mStreams[stream].mIndexCur, output, device, delayMs); // ++++++++++++++++++++++++++AudioPolicyManagerBase::checkAndSetVolume++++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::applyStreamVolumes 进入： status_t AudioPolicyManagerBase::checkAndSetVolume(int stream, int index, audio_io_handle_t output, uint32_t device, int delayMs, bool force /* = false */) { // do not change actual stream volume if the stream is muted // 如果 stream 是 mute ，并不真正去改变其音量 if (mOutputs.valueFor(output)->mMuteCount[stream] != 0) { LOGV("checkAndSetVolume() stream %d muted count %d", stream, mOutputs.valueFor(output)->mMuteCount[stream]); return NO_ERROR; } // do not change in call volume if bluetooth is connected and vice versa // 如果链接了蓝牙耳机，则不去改变 VOICE_CALL 的音量，反之亦然 if ((stream == AudioSystem::VOICE_CALL && mForceUse[AudioSystem::FOR_COMMUNICATION] == AudioSystem::FORCE_BT_SCO) || (stream == AudioSystem::BLUETOOTH_SCO && mForceUse[AudioSystem::FOR_COMMUNICATION] != AudioSystem::FORCE_BT_SCO)) { LOGV("checkAndSetVolume() cannot set stream %d volume with force use = %d for comm", stream, mForceUse[AudioSystem::FOR_COMMUNICATION]); return INVALID_OPERATION; } float volume = computeVolume(stream, index, output, device); // +++++++++++++++++++++++++++AudioPolicyManagerBase::computeVolume+++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::checkAndSetVolume 进入： float AudioPolicyManagerBase::computeVolume(int stream, int index, audio_io_handle_t output, uint32_t device) { float volume = 1.0; AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output); StreamDescriptor &streamDesc = mStreams[stream]; if (device == 0) { device = outputDesc->device(); } int volInt = (100 * (index - streamDesc.mIndexMin)) / (streamDesc.mIndexMax - streamDesc.mIndexMin); volume = AudioSystem::linearToLog(volInt); // ++++++++++++++++++++++++++AudioSystem::linearToLog++++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::computeVolume 进入： // convert volume steps to natural log scale // change this value to change volume scaling static const float dBPerStep = 0.5f; // shouldn't need to touch these static const float dBConvert = -dBPerStep * 2.302585093f / 20.0f; static const float dBConvertInverse = 1.0f / dBConvert; float AudioSystem::linearToLog(int volume) { // float v = volume ? exp(float(100 - volume) * dBConvert) : 0; // LOGD("linearToLog(%d)=%f", volume, v); // return v; return volume ? exp(float(100 - volume) * dBConvert) : 0; } // 返回到函数 AudioPolicyManagerBase::computeVolume // --------------------------AudioSystem::linearToLog-------------------------------------- // if a headset is connected, apply the following rules to ring tones and notifications // to avoid sound level bursts in user's ears: // - always attenuate ring tones and notifications volume by 6dB // - if music is playing, always limit the volume to current music volume, // with a minimum threshold at -36dB so that notification is always perceived. // 如果连接了耳机，为了防止在用户耳朵中产生爆音，对铃声和警告声需要使用以下规则： // - 对铃声和警告声总是减弱 6dB。 // - 如果正在播放音乐，铃声和警告声不应该高于音乐声音， // 不过，下限是 -36dB if ((device & (AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP | AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES | AudioSystem::DEVICE_OUT_WIRED_HEADSET | AudioSystem::DEVICE_OUT_WIRED_HEADPHONE)) && ((getStrategy((AudioSystem::stream_type)stream) == STRATEGY_SONIFICATION) || (stream == AudioSystem::SYSTEM)) && streamDesc.mCanBeMuted) { // Attenuation applied to STRATEGY_SONIFICATION streams when a headset is connected: 6dB // #define SONIFICATION_HEADSET_VOLUME_FACTOR 0.5 volume *= SONIFICATION_HEADSET_VOLUME_FACTOR; // when the phone is ringing we must consider that music could have been paused just before // by the music application and behave as if music was active if the last music track was // just stopped if (outputDesc->mRefCount[AudioSystem::MUSIC] || mLimitRingtoneVolume) { float musicVol = computeVolume(AudioSystem::MUSIC, mStreams[AudioSystem::MUSIC].mIndexCur, output, device); // Min volume for STRATEGY_SONIFICATION streams when limited by music volume: -36dB // #define SONIFICATION_HEADSET_VOLUME_MIN 0.016 float minVol = (musicVol > SONIFICATION_HEADSET_VOLUME_MIN) ? musicVol : SONIFICATION_HEADSET_VOLUME_MIN; if (volume > minVol) { volume = minVol; LOGV("computeVolume limiting volume to %f musicVol %f", minVol, musicVol); } } } return volume; } // 返回到函数 AudioPolicyManagerBase::checkAndSetVolume // ---------------------------AudioPolicyManagerBase::computeVolume------------------------------------- // We actually change the volume if: // - the float value returned by computeVolume() changed // - the force flag is set // 只有当 compute 返回的音量与当前的音量不同，或者强制要求改音量时，才会去真正改变音量 if (volume != mOutputs.valueFor(output)->mCurVolume[stream] || force) { mOutputs.valueFor(output)->mCurVolume[stream] = volume; LOGV("setStreamVolume() for output %d stream %d, volume %f, delay %d", output, stream, volume, delayMs); if (stream == AudioSystem::VOICE_CALL || stream == AudioSystem::DTMF || stream == AudioSystem::BLUETOOTH_SCO) { // offset value to reflect actual hardware volume that never reaches 0 // 1% corresponds roughly to first step in VOICE_CALL stream volume setting (see AudioService.java) volume = 0.01 + 0.99 * volume; } mpClientInterface->setStreamVolume((AudioSystem::stream_type)stream, volume, output, delayMs); // +++++++++++++++++++++++++++AudioPolicyService::setStreamVolume+++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::checkAndSetVolume 进入： status_t AudioPolicyService::setStreamVolume(AudioSystem::stream_type stream, float volume, audio_io_handle_t output, int delayMs) { // 函数 AudioPolicyService::AudioCommandThread::volumeCommand 会调用函数 AudioPolicyService::AudioCommandThread::insertCommand_l // 往 mAudioCommands 中添加成员。 // 函数 AudioPolicyService::AudioCommandThread::threadLoop 会处理 mAudioCommands 中的成员 // 对于 SET_VOLUME 命令，调用了函数 AudioSystem::setStreamVolume return mAudioCommandThread->volumeCommand((int)stream, volume, (int)output, delayMs); // +++++++++++++++++++++++++++++AudioSystem::setStreamVolume+++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyService::setStreamVolume 进入： status_t AudioSystem::setStreamVolume(int stream, float value, int output) { if (uint32_t(stream) >= NUM_STREAM_TYPES) return BAD_VALUE; const sp<IAudioFlinger>& af = AudioSystem::get_audio_flinger(); if (af == 0) return PERMISSION_DENIED; af->setStreamVolume(stream, value, output); // ++++++++++++++++++++++++++++AudioFlinger::setStreamVolume++++++++++++++++++++++++++++++++++++ // 从函数 AudioSystem::setStreamVolume 进入： status_t AudioFlinger::setStreamVolume(int stream, float value, int output) { // check calling permissions if (!settingsAllowed()) { return PERMISSION_DENIED; } if (stream < 0 || uint32_t(stream) >= AudioSystem::NUM_STREAM_TYPES) { return BAD_VALUE; } AutoMutex lock(mLock); PlaybackThread *thread = NULL; if (output) { thread = checkPlaybackThread_l(output); if (thread == NULL) { return BAD_VALUE; } } mStreamTypes[stream].volume = value; if (thread == NULL) { for (uint32_t i = 0; i < mPlaybackThreads.size(); i++) { mPlaybackThreads.valueAt(i)->setStreamVolume(stream, value); } } else { thread->setStreamVolume(stream, value); // +++++++++++++++++++++++++++++AudioFlinger::PlaybackThread::setStreamVolume+++++++++++++++++++++++++++++++++++ // 从函数 AudioFlinger::setStreamVolume 进入： status_t AudioFlinger::PlaybackThread::setStreamVolume(int stream, float value) { #ifdef LVMX int audioOutputType = LifeVibes::getMixerType(mId, mType); if (LifeVibes::audioOutputTypeIsLifeVibes(audioOutputType)) { LifeVibes::setStreamVolume(audioOutputType, stream, value); } #endif // 这一块在看 testPlaybackHeadPositionIncrease 代码的时候已经介绍过 mStreamTypes[stream].volume = value; return NO_ERROR; } // 返回到函数 AudioFlinger::setStreamVolume // ------------------------------AudioFlinger::PlaybackThread::setStreamVolume---------------------------------- } return NO_ERROR; } // 返回到函数 AudioSystem::setStreamVolume // ----------------------------AudioFlinger::setStreamVolume------------------------------------ return NO_ERROR; } // 返回到函数 AudioPolicyService::setStreamVolume // -----------------------------AudioSystem::setStreamVolume----------------------------------- } // 返回到函数 AudioPolicyManagerBase::checkAndSetVolume // ---------------------------AudioPolicyService::setStreamVolume------------------------------------- } if (stream == AudioSystem::VOICE_CALL || stream == AudioSystem::BLUETOOTH_SCO) { float voiceVolume; // Force voice volume to max for bluetooth SCO as volume is managed by the headset if (stream == AudioSystem::VOICE_CALL) { voiceVolume = (float)index/(float)mStreams[stream].mIndexMax; } else { voiceVolume = 1.0; } if (voiceVolume != mLastVoiceVolume && output == mHardwareOutput) { // 这儿与 setStreamVolume 函数类似，最终调用到了函数 AudioFlinger::setVoiceVolume // 不过，setVoiceVolume最终会调用底层接口，改变硬件音量 // 这一块也在看 testPlaybackHeadPositionIncrease 代码的时候有看过 mpClientInterface->setVoiceVolume(voiceVolume, delayMs); mLastVoiceVolume = voiceVolume; } } return NO_ERROR; } // 返回到函数 AudioPolicyManagerBase::applyStreamVolumes // --------------------------AudioPolicyManagerBase::checkAndSetVolume-------------------------------------- } } // 返回到函数 AudioPolicyManagerBase::setOutputDevice // -------------------------AudioPolicyManagerBase::applyStreamVolumes--------------------------------------- // if changing from a combined headset + speaker route, unmute media streams // 前面，如果该条件成立，我们做了 mute 操作，此处要做恢复 if (output == mHardwareOutput && AudioSystem::popCount(prevDevice) == 2) { setStrategyMute(STRATEGY_MEDIA, false, output, delayMs); } } // 返回到函数 AudioPolicyManagerBase::startOutput // ----------------------------AudioPolicyManagerBase::setOutputDevice------------------------------------ // handle special case for sonification while in call if (isInCall()) { handleIncallSonification(stream, true, false); // ++++++++++++++++++++++++++++AudioPolicyManagerBase::handleIncallSonification++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::startOutput 进入： void AudioPolicyManagerBase::handleIncallSonification(int stream, bool starting, bool stateChange) { // if the stream pertains to sonification strategy and we are in call we must // mute the stream if it is low visibility. If it is high visibility, we must play a tone // in the device used for phone strategy and play the tone if the selected device does not // interfere with the device used for phone strategy // if stateChange is true, we are called from setPhoneState() and we must mute or unmute as // many times as there are active tracks on the output // 如果 stream 是 sonification strategy 的，并且其可见性低， 如果有电话打入则 mute 该 stream 。 // 如果其可见性高，我们必须在 phone strategy 使用的 device 中播放 tone ，并且如果选定的 device // 与 phone strategy 不相干的话，也要播放 tone 。 // 如果 stateChange 是 true ，则我们肯定是从函数 setPhoneState 进来的， // 我们必须 mute / unmute output 中所有的 active track 。 if (getStrategy((AudioSystem::stream_type)stream) == STRATEGY_SONIFICATION) { AudioOutputDescriptor *outputDesc = mOutputs.valueFor(mHardwareOutput); LOGV("handleIncallSonification() stream %d starting %d device %x stateChange %d", stream, starting, outputDesc->mDevice, stateChange); if (outputDesc->mRefCount[stream]) { // 只有 output 中存在 active 的该类型的 stream 时才做处理 int muteCount = 1; if (stateChange) { muteCount = outputDesc->mRefCount[stream]; } if (AudioSystem::isLowVisibility((AudioSystem::stream_type)stream)) { // ++++++++++++++++++++++++++++AudioSystem::isLowVisibility++++++++++++++++++++++++++++++++++++ // 从函数 AudioPolicyManagerBase::handleIncallSonification 进入： bool AudioSystem::isLowVisibility(stream_type stream) { // 以下这几种 stream 的可见性低，其他的都是高的 if (stream == AudioSystem::SYSTEM || stream == AudioSystem::NOTIFICATION || stream == AudioSystem::RING) { return true; } else { return false; } } // 返回到函数 AudioPolicyManagerBase::handleIncallSonification // ----------------------------AudioSystem::isLowVisibility------------------------------------ LOGV("handleIncallSonification() low visibility, muteCount %d", muteCount); for (int i = 0; i < muteCount; i++) { setStreamMute(stream, starting, mHardwareOutput); } } else { LOGV("handleIncallSonification() high visibility"); if (outputDesc->device() & getDeviceForStrategy(STRATEGY_PHONE)) { LOGV("handleIncallSonification() high visibility muted, muteCount %d", muteCount); for (int i = 0; i < muteCount; i++) { setStreamMute(stream, starting, mHardwareOutput); } } if (starting) { mpClientInterface->startTone(ToneGenerator::TONE_SUP_CALL_WAITING, AudioSystem::VOICE_CALL); } else { mpClientInterface->stopTone(); } } } } } // 返回到函数 AudioPolicyManagerBase::startOutput // ----------------------------AudioPolicyManagerBase::handleIncallSonification------------------------------------ } // apply volume rules for current stream and device if necessary checkAndSetVolume(stream, mStreams[stream].mIndexCur, output, outputDesc->device()); return NO_ERROR; } // 返回到函数 AudioPolicyService::startOutput // -----------------------------AudioPolicyManagerBase::startOutput----------------------------------- } // 返回到函数 AudioSystem::startOutput // -----------------------------AudioPolicyService::startOutput----------------------------------- } // 返回到函数 AudioFlinger::PlaybackThread::Track::start // ----------------------------AudioSystem::startOutput------------------------------------ thread->mLock.lock(); } if (status == NO_ERROR) { PlaybackThread *playbackThread = (PlaybackThread *)thread.get(); playbackThread->addTrack_l(this); } else { mState = state; } } else { status = BAD_VALUE; } return status; }
###########################################################


&&&&&&&&&&&&&&&&&&&&&&&总结&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
各种声音控制策略的实现主要在 Audio Policy Manager 中。
其中会根据 stream type 和当前的状态对各种 stream 的音量作必要的修改。
以达成以下的优先级效果：


Priority  Strategy Type                           Stream Type
4            STRATEGY_PHONE               VOICE_CALL
                                                                   BLUETOOTH_SCO
3           STRATEGY_SONIFICATION    RING
                                                                   NOTIFICATION
                                                                   ALARM
                                                                   ENFORCED_AUDIBLE
2          STRATEGY_MEDIA                   SYSTEM
                                                                  TTS
                                                                   MUSIC
1         STRATEGY_DTMF                      DTMF


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