Android Audio音量设置流程

转载自http://blog.axlecho.com/audioyin-liang-she-zhi-liu-cheng/

Audio音量调节是一级一级调节，而且分不同的流类型，如响铃，通话，多媒体等。不同的设备(蓝牙设备)的设置方法有所区别。

sdk的api，设置相应流的音量。不同的流index的范围不一样

//--->frameworks/base/media/java/android/media/AudioManager.java
public void setStreamVolume(int streamType, int index, int flags) {IAudioService service = getService();try {service.setStreamVolume(streamType, index, flags, getContext().getOpPackageName());} catch (RemoteException e) {Log.e(TAG, "Dead object in setStreamVolume", e);}
}

java层Service实现,volume的调节的实现是用state模式来实现，可能需要原子性或不同的模式下调节音量的操作不同。

//--->frameworks/base/services/core/java/com/android/server/audio/AudioService.java
private void setStreamVolume(int streamType, int index, int flags, String callingPackage,String caller, int uid) {...(检查参数)...(转换参数)// 获取设备final int device = getDeviceForStream(streamType);...(特殊处理a2dp)...(检查uid，实体按键调节音量需要判断当前用户？)synchronized (mSafeMediaVolumeState) {mPendingVolumeCommand = null;oldIndex = streamState.getIndex(device);index = rescaleIndex(index * 10, streamType, streamTypeAlias);...(特殊处理a2dp)...(特殊处理HDMI)...(设置一些标志位，如标记一些不可调节音量的设备)//检查当前是否可设置音量if (!checkSafeMediaVolume(streamTypeAlias, index, device)) {// 不可以则生成PendingCommand，等待合适的时机mVolumeController.postDisplaySafeVolumeWarning(flags);mPendingVolumeCommand = new StreamVolumeCommand(streamType, index, flags, device);} else {// 设置音量onSetStreamVolume(streamType, index, flags, device, caller);index = mStreamStates[streamType].getIndex(device);}}// 发送更新音量信息sendVolumeUpdate(streamType, oldIndex, index, flags);
}private void onSetStreamVolume(int streamType, int index, int flags, int device,String caller) {final int stream = mStreamVolumeAlias[streamType];// 设置音量setStreamVolumeInt(stream, index, device, false, caller);...(判断音量是否为0，调节模式(静音或响铃))mStreamStates[stream].mute(index == 0);
}private void setStreamVolumeInt(int streamType,int index,int device,boolean force,String caller) {VolumeStreamState streamState = mStreamStates[streamType];if (streamState.setIndex(index, device, caller) || force) {// Post message to set system volume (it in turn will post a message// to persist).sendMsg(mAudioHandler,MSG_SET_DEVICE_VOLUME,SENDMSG_QUEUE,device,0,streamState,0);}
}@Override
public void handleMessage(Message msg) {...switch (msg.what) {case MSG_SET_DEVICE_VOLUME:setDeviceVolume((VolumeStreamState) msg.obj, msg.arg1);break;...}...
}private void setDeviceVolume(VolumeStreamState streamState, int device) {synchronized (VolumeStreamState.class) {// 设置音量streamState.applyDeviceVolume_syncVSS(device);...(Apply change to all streams using this one as alias)}// Post a persist volume msgsendMsg(mAudioHandler,MSG_PERSIST_VOLUME,SENDMSG_QUEUE,device,0,streamState,PERSIST_DELAY);
}public void applyDeviceVolume_syncVSS(int device) {int index;if (mIsMuted) {index = 0;} else if (((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 && mAvrcpAbsVolSupported) || ((device & mFullVolumeDevices) != 0)) {index = (mIndexMax + 5)/10;} else {index = (getIndex(device) + 5)/10;}AudioSystem.setStreamVolumeIndex(mStreamType, index, device);
}

AudioSystem的setStreamVolumeIndex是个native函数，从这里到跳到c++代码

//--->frameworks/base/media/java/android/media/AudioSystem.java
public static native int setStreamVolumeIndex(int stream, int index,int device);

jni的代码没做处理，直接转发给c++层的AudioSystem

//--->frameworks/base/core/jni/android_media_AudioSystem.cpp
static JNINativeMethod gMethods[] = { ...{"setStreamVolumeIndex","(III)I",   (void *)android_media_AudioSystem_setStreamVolumeIndex},
...};static jint android_media_AudioSystem_setStreamVolumeIndex(JNIEnv *env,jobject thiz,jint stream,jint index,jint device)
{return (jint) check_AudioSystem_Command(AudioSystem::setStreamVolumeIndex(static_cast <audio_stream_type_t>(stream),index,(audio_devices_t)device));
}

AudioSystem又踢给AudioPolicyService(这里是binder通信，从这里跳到服务端处理)

//--->frameworks/av/media/libmedia/AudioSystem.cpp
status_t AudioSystem::setStreamVolumeIndex(audio_stream_type_t stream,int index,audio_devices_t device)
{const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();if (aps == 0) return PERMISSION_DENIED;return aps->setStreamVolumeIndex(stream, index, device);
}

AudioPolicyService做了些权限和参数检查，转发给AudioPolicyManager

//---frameworks/av/services/audiopolicy/service/AudioPolicyService.cpp
status_t AudioPolicyService::setStreamVolumeIndex(audio_stream_type_t stream,int index,audio_devices_t device)
{if (mAudioPolicyManager == NULL) return NO_INIT;if (!settingsAllowed()) return PERMISSION_DENIED;if (uint32_t(stream) >= AUDIO_STREAM_PUBLIC_CNT) return BAD_VALUE;Mutex::Autolock _l(mLock);return mAudioPolicyManager->setStreamVolumeIndex(stream,index,device);
}

AudioPolicyManager的处理比较复杂，主要是包括了音频策略的判断

//--->frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
status_t AudioPolicyManager::setStreamVolumeIndex(audio_stream_type_t stream,int index,audio_devices_t device)
{...(检查音量及设备是否为audio设备)...(策略判断)if ((device != AUDIO_DEVICE_OUT_DEFAULT) && (device & (strategyDevice | accessibilityDevice)) == 0) {return NO_ERROR;}...(设置每个输出设备的音量)status_t volStatus = checkAndSetVolume(stream, index, desc, curDevice);...
}status_t AudioPolicyManager::checkAndSetVolume(audio_stream_type_t stream,int index,const sp<AudioOutputDescriptor>& outputDesc,audio_devices_t device,int delayMs,bool force)
{...(do not change actual stream volume if the stream is muted)...(do not change in call volume if bluetooth is connected and vice versa)// 声音等级与真正参数的转换float volumeDb = computeVolume(stream, index, device);  // 设置输出设备的声音outputDesc->setVolume(volumeDb, stream, device, delayMs, force);// 设置通话的音量？？if (stream == AUDIO_STREAM_VOICE_CALL || stream == AUDIO_STREAM_BLUETOOTH_SCO) {...mpClientInterface->setVoiceVolume(voiceVolume, delayMs);...}}return NO_ERROR;
}

AudioOutputDescriptor是音频设备描述符，outputDesc是SwAudioOutputDescriptor类型。

//--->/frameworks/av/services/audiopolicy/common/managerdefinitions/src/AudioOutputDescriptor.cppbool AudioOutputDescriptor::setVolume(float volume,audio_stream_type_t stream,audio_devices_t device __unused,uint32_t delayMs,bool force)
{// We actually change the volume if:// - the float value returned by computeVolume() changed// - the force flag is setif (volume != mCurVolume[stream] || force) {ALOGV("setVolume() for stream %d, volume %f, delay %d", stream, volume, delayMs);mCurVolume[stream] = volume;return true;}return false;
}bool SwAudioOutputDescriptor::setVolume(float volume,audio_stream_type_t stream,audio_devices_t device,uint32_t delayMs,bool force)
{bool changed = AudioOutputDescriptor::setVolume(volume, stream, device, delayMs, force);if (changed) {// Force VOICE_CALL to track BLUETOOTH_SCO stream volume when bluetooth audio is// enabledfloat volume = Volume::DbToAmpl(mCurVolume[stream]);if (stream == AUDIO_STREAM_BLUETOOTH_SCO) {mClientInterface->setStreamVolume(AUDIO_STREAM_VOICE_CALL, volume,mIoHandle, delayMs);}mClientInterface->setStreamVolume(stream, volume, mIoHandle, delayMs);}return changed;
}

AudioOutputDescriptor的mClientInterface是AudioPolicyService，所以会转到AudioPolicyService的setStreamVolume
AudioPolicyService异步执行这个操作,最后会转到AudioSystem的setStreamVolume。

//--->frameworks/av/services/audiopolicy/service/AudioPolicyService.cpp
int AudioPolicyService::setStreamVolume(audio_stream_type_t stream,float volume,audio_io_handle_t output,int delayMs)
{return (int)mAudioCommandThread->volumeCommand(stream, volume,output, delayMs);
}status_t AudioPolicyService::AudioCommandThread::volumeCommand(audio_stream_type_t stream,float volume,audio_io_handle_t output,int delayMs)
{...(封装了一下data跟command)return sendCommand(command, delayMs);
}status_t AudioPolicyService::AudioCommandThread::sendCommand(sp<AudioCommand>& command, int delayMs) {...(一些命令队列的操作)}// 处理函数
bool AudioPolicyService::AudioCommandThread::threadLoop()
{...while (!exitPending()){...switch (command->mCommand) {...case SET_VOLUME: ...(Lock)VolumeData *data = (VolumeData *)command->mParam.get();command->mStatus = AudioSystem::setStreamVolume(data->mStream,data->mVolume,data->mIO);break;...}
}

AudioSystem又转到AudioFlinger

//--->frameworks/av/media/libmedia/AudioSystem.cpp
status_t AudioSystem::setStreamVolume(audio_stream_type_t stream, float value,audio_io_handle_t output)
{...(权限参数检查)af->setStreamVolume(stream, value, output);return NO_ERROR;
}

AudioFlinger会去获取output对应的PlaybackThread并设置PlaybackThread的音量，如果output == AUDIOIOHANDLE_NONE，则设置所有PlaybackThread的音量。

//--->frameworks/av/services/audioflinger/AudioFlinger.cpp
status_t AudioFlinger::setStreamVolume(audio_stream_type_t stream, float value,audio_io_handle_t output)
{...(权限检查)...(流类型检查)AutoMutex lock(mLock);...(获取对应设备的PlaybackTread)// ???mStreamTypes[stream].volume = value;if (thread == NULL) {   // output == AUDIO_IO_HANDLE_NONEfor (size_t i = 0; i < mPlaybackThreads.size(); i++) {mPlaybackThreads.valueAt(i)->setStreamVolume(stream, value);}} else {thread->setStreamVolume(stream, value);}return NO_ERROR;
}

PlaybackThread设置mStreamTypes的volume。并唤醒PlaybackThread线程

void AudioFlinger::PlaybackThread::setStreamVolume(audio_stream_type_t stream, float value)
{Mutex::Autolock _l(mLock);mStreamTypes[stream].volume = value;broadcast_l();
}

不同类型的Thread貌似有不同使用方法 MixerThread是在prepareTracks_l里使用，最后会设置AudioMixer的参数

//--->frameworks/av/services/audioflinger/Threads.cpp
AudioFlinger::PlaybackThread::mixer_state AudioFlinger::MixerThread::prepareTracks_l(Vector< sp<Track> > *tracksToRemove) {...// FastTracktrack->mCachedVolume = masterVolume * mStreamTypes[track->streamType()].volume;...// NormalTrack// 这里涉及到了左右声道的音量的计算// compute volume for this trackuint32_t vl, vr;       // in U8.24 integer formatfloat vlf, vrf, vaf;   // in [0.0, 1.0] float formatfloat typeVolume = mStreamTypes[track->streamType()].volume;float v = masterVolume * typeVolume;...//计算完设置混音器的参数mAudioMixer->setParameter(name, param, AudioMixer::VOLUME0, &vlf);mAudioMixer->setParameter(name, param, AudioMixer::VOLUME1, &vrf);mAudioMixer->setParameter(name, param, AudioMixer::AUXLEVEL, &vaf);...
}// 最后会调用到mAudioMixer的setVolumeRampVariables
static inline bool setVolumeRampVariables(float newVolume, int32_t ramp,int16_t *pIntSetVolume, int32_t *pIntPrevVolume, int32_t *pIntVolumeInc,float *pSetVolume, float *pPrevVolume, float *pVolumeInc){...}

DirectOutputThread在processVolumel里使用(processVolumel在prepareTracksl中被调用)
processVolumel直接设置了输出设备的volume

//--->frameworks/av/services/audioflinger/Threads.cpp
void AudioFlinger::DirectOutputThread::processVolume_l(Track *track, bool lastTrack) {...float typeVolume = mStreamTypes[track->streamType()].volume;float v = mMasterVolume * typeVolume;...(一系列的设置)if (mOutput->stream->set_volume) {mOutput->stream->set_volume(mOutput->stream, left, right);}
}

还有其他的几种Thread都是上面两种Thread的子类，处理方式是一致的

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