Android 9 按音量键音量调节流程

参考：https://blog.csdn.net/kehyuanyu/article/details/49153223
https://blog.csdn.net/qq_34787560/article/details/97374073?utm_medium=distribute.pc_aggpage_search_result.none-task-blog-2_{aggregatepage}first_rank_v2~rank_aggregation-7-97374073.pc_agg_rank_aggregation&utm_term=android+%E9%9F%B3%E9%87%8F%E6%8C%89%E9%94%AE%E6%B5%81%E7%A8%8B&spm=1000.2123.3001.4430

基于android 9平台分析。
在Android系统中，默认的设备(phone等)音量都是分开控制的，这些包括媒体、铃声、闹铃、蓝牙、通话通过音频流来区别不同的音量类型。每种流类型都定义最大音量、最小音量及默认音量，Android 9定了了11中音频流类型：

流类型

//frameworks/base/media/java/android/media/AudioSystem.javapublic static final String[] STREAM_NAMES = new String[] {"STREAM_VOICE_CALL","STREAM_SYSTEM","STREAM_RING","STREAM_MUSIC","STREAM_ALARM","STREAM_NOTIFICATION","STREAM_BLUETOOTH_SCO","STREAM_SYSTEM_ENFORCED","STREAM_DTMF","STREAM_TTS","STREAM_ACCESSIBILITY"};

最大音量（音量等级）

//frameworks/base/services/core/java/com/android/server/audio/AudioService.java/** Maximum volume index values for audio streams */protected static int[] MAX_STREAM_VOLUME = new int[] {5,  // STREAM_VOICE_CALL7,  // STREAM_SYSTEM7,  // STREAM_RING15, // STREAM_MUSIC7,  // STREAM_ALARM7,  // STREAM_NOTIFICATION15, // STREAM_BLUETOOTH_SCO7,  // STREAM_SYSTEM_ENFORCED15, // STREAM_DTMF15, // STREAM_TTS15  // STREAM_ACCESSIBILITY};

根据音量曲线表，一般情况音量等级最大可以设置为100。但是，有些音频音量调节并不经过音箱曲线表，而是直接调用HAL层的set_volume，而HAL层对音量又做了类似“音量曲线”的转换。所有修改音量级别，可能会有以下问题：
1、调至15时音量已经最大，15级以上的音量等级无效。
比如amlogic T972将MAX_STREAM_VOLUME 调整为30等级，HAL层audio_hw.c对音量调节：out_set_volume()–>volume2Ms12DBGain()–>AmplToDb()，因15等级时DB值已经“够大”，再往上调音量变化不明显，修改如下：

2、调节音量时音量过大导致输出波形失真。
因喇叭性能或功放电路的原因（最好改电路，否则产品声音小），CPU音量输出增益不能太大，否则引起波形失真。比如Mst358在HAL层audio_hw.c对音量调节：

最小音量

//frameworks/base/services/core/java/com/android/server/audio/AudioService.java/** Minimum volume index values for audio streams */protected static int[] MIN_STREAM_VOLUME = new int[] {1,  // STREAM_VOICE_CALL0,  // STREAM_SYSTEM0,  // STREAM_RING0,  // STREAM_MUSIC1,  // STREAM_ALARM0,  // STREAM_NOTIFICATION0,  // STREAM_BLUETOOTH_SCO0,  // STREAM_SYSTEM_ENFORCED0,  // STREAM_DTMF0,  // STREAM_TTS1   // STREAM_ACCESSIBILITY};

设置最小音量的目的是有些音频不能单独设置为静音。

默认音量

//frameworks/base/media/java/android/media/AudioSystem.javapublic static int[] DEFAULT_STREAM_VOLUME = new int[] {4,  // STREAM_VOICE_CALL7,  // STREAM_SYSTEM0,  // STREAM_RING5, // STREAM_MUSIC0,  // STREAM_ALARM5,  // STREAM_NOTIFICATION7,  // STREAM_BLUETOOTH_SCO7,  // STREAM_SYSTEM_ENFORCED5, // STREAM_DTMF5, // STREAM_TTS5, // STREAM_ACCESSIBILITY};

音频流映射StreamAlias

不同设备的映射定义不同，系统中一共定义三种设备的音频流的映射，分别是STREAM_VOLUME_ALIAS_VOICE，STREAM_VOLUME_ALIAS_TELEVISION，STREAM_VOLUME_ALIAS_DEFAULT

StreamAlias存在的意义：流类型别名，某音频流的行为等同于另外一种音频流，可以将它映射为另一种音频流，比如AudioSystem.STREAM_RING用作AudioSystem.STREAM_MUSIC来处理。

StreamAlias实际使用的意义是，Android为了兼容各种设备，定义了尽可能多的音频流。但是，在有些简单的设备中，可能仅有一个喇叭，所以对音频操作没有必要区分音频流。所以通过StreamAlias，在手机和平板上实际上能调节的就是五种音量，在TV和就机顶盒之类设备能调节的仅仅一种音量即music，故如有需求需要统一音量的可以将当前的音频流改为TV类型。
调用AudioSsytem::getPlatformType()可知道系统是手机、平板或TV类型。

//frameworks/base/services/core/java/com/android/server/audio/AudioService.java
1.voice--具有语音功能的设备，电话等
private final int[] STREAM_VOLUME_ALIAS_VOICE = new int[] {AudioSystem.STREAM_VOICE_CALL,      // STREAM_VOICE_CALLAudioSystem.STREAM_RING,            // STREAM_SYSTEMAudioSystem.STREAM_RING,            // STREAM_RINGAudioSystem.STREAM_MUSIC,           // STREAM_MUSICAudioSystem.STREAM_ALARM,           // STREAM_ALARMAudioSystem.STREAM_RING,            // STREAM_NOTIFICATIONAudioSystem.STREAM_BLUETOOTH_SCO,   // STREAM_BLUETOOTH_SCOAudioSystem.STREAM_RING,            // STREAM_SYSTEM_ENFORCEDAudioSystem.STREAM_RING,            // STREAM_DTMFAudioSystem.STREAM_MUSIC            // STREAM_TTS
};
2. television--电视机顶盒或投影设备
private final int[] STREAM_VOLUME_ALIAS_TELEVISION = new int[] {AudioSystem.STREAM_MUSIC,       // STREAM_VOICE_CALLAudioSystem.STREAM_MUSIC,       // STREAM_SYSTEMAudioSystem.STREAM_MUSIC,       // STREAM_RINGAudioSystem.STREAM_MUSIC,       // STREAM_MUSICAudioSystem.STREAM_MUSIC,       // STREAM_ALARMAudioSystem.STREAM_MUSIC,       // STREAM_NOTIFICATIONAudioSystem.STREAM_MUSIC,       // STREAM_BLUETOOTH_SCOAudioSystem.STREAM_MUSIC,       // STREAM_SYSTEM_ENFORCEDAudioSystem.STREAM_MUSIC,       // STREAM_DTMFAudioSystem.STREAM_MUSIC        // STREAM_TTS
};
3. default--平板之类的设备
private final int[] STREAM_VOLUME_ALIAS_DEFAULT = new int[] {AudioSystem.STREAM_VOICE_CALL,      // STREAM_VOICE_CALLAudioSystem.STREAM_RING,            // STREAM_SYSTEMAudioSystem.STREAM_RING,            // STREAM_RINGAudioSystem.STREAM_MUSIC,           // STREAM_MUSICAudioSystem.STREAM_ALARM,           // STREAM_ALARMAudioSystem.STREAM_RING,            // STREAM_NOTIFICATIONAudioSystem.STREAM_BLUETOOTH_SCO,   // STREAM_BLUETOOTH_SCOAudioSystem.STREAM_RING,            // STREAM_SYSTEM_ENFORCEDAudioSystem.STREAM_RING,            // STREAM_DTMFAudioSystem.STREAM_MUSIC            // STREAM_TTS
};

音量按键处理流程

在Android平台上，音量键，主页键(home),都是全局按键，但是主页键是个例外不能被应用所捕获。下面分析一下音量按键的流程，主要从framework层处理开始，至于EventHub 从驱动的/dev/input/event0获取按键信息到上抛属于Android input 系统方面的流程。

系统层接收音量按键

ViewRootImpl.processKeyEvent 处理Activity 上面收到的按键

private int processKeyEvent(QueuedInputEvent q) {final KeyEvent event = (KeyEvent)q.mEvent;if (mUnhandledKeyManager.preViewDispatch(event)) {return FINISH_HANDLED;}// Deliver the key to the view hierarchy.if (mView.dispatchKeyEvent(event)) {return FINISH_HANDLED;}if (shouldDropInputEvent(q)) {return FINISH_NOT_HANDLED;}。。。。。}

从中可以看到mView.dispatchKeyEvent(event),完成将按键发送给Activity处理，由于每个Activity都是view的子类，所有这些按键将dispatchKeyEvent传递给onKeyDown：

   /*** Called to process key events.  You can override this to intercept all* key events before they are dispatched to the window.  Be sure to call* this implementation for key events that should be handled normally.** @param event The key event.** @return boolean Return true if this event was consumed.*/public boolean dispatchKeyEvent(KeyEvent event) {onUserInteraction();// Let action bars open menus in response to the menu key prioritized over// the window handling itfinal int keyCode = event.getKeyCode();if (keyCode == KeyEvent.KEYCODE_MENU &&mActionBar != null && mActionBar.onMenuKeyEvent(event)) {return true;}Window win = getWindow();if (win.superDispatchKeyEvent(event)) {return true;}View decor = mDecor;if (decor == null) decor = win.getDecorView();return event.dispatch(this, decor != null? decor.getKeyDispatcherState() : null, this);}

注意这个方法可以被子类覆盖。
win.superDispatchKeyEvent()不处理音量键，调用根View的dispatchKeyEvent，进而调用ViewGroup的dispatchKeyEvent，如果都没处理，则调用View的dispatchKeyEvent：

    public boolean dispatchKeyEvent(KeyEvent event) {if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onKeyEvent(event, 0);}// Give any attached key listener a first crack at the event.//noinspection SimplifiableIfStatementListenerInfo li = mListenerInfo;if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) {return true;}if (event.dispatch(this, mAttachInfo != null? mAttachInfo.mKeyDispatchState : null, this)) {return true;}if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);}return false;}

通过event.dispatch进一步分发

//framework/base/core/java/android/view/KeyEvent.javapublic final boolean dispatch(Callback receiver, DispatcherState state,Object target) {switch (mAction) {case ACTION_DOWN: {mFlags &= ~FLAG_START_TRACKING;if (DEBUG) Log.v(TAG, "Key down to " + target + " in " + state+ ": " + this);boolean res = receiver.onKeyDown(mKeyCode, this);if (state != null) {if (res && mRepeatCount == 0 && (mFlags&FLAG_START_TRACKING) != 0) {if (DEBUG) Log.v(TAG, "  Start tracking!");state.startTracking(this, target);} else if (isLongPress() && state.isTracking(this)) {try {if (receiver.onKeyLongPress(mKeyCode, this)) {if (DEBUG) Log.v(TAG, "  Clear from long press!");state.performedLongPress(this);res = true;}} catch (AbstractMethodError e) {}}}return res;}......}

上面只关注了ACTION_DOWN的处理。KeyEvent.dispatch通过receiver.onKeyDown将最终的按键消息发送给当前的Activity，而receiver即为KeyEvent.Callback的实现类(View的子类等等)，至此如果上面上传应用处理完了就会返回，如果没有处理就会流向mFallbackEventHandler.dispatchKeyEvent(event),其实mFallbackEventHandler就是PhoneFallbackEventHandler,接着看 PhoneFallbackEventHandler.dispatchKeyEvent的处理流程

//framework/base/core/java/com/android/internal/policy/PhoneFallbackEventHandler.javapublic boolean dispatchKeyEvent(KeyEvent event) {final int action = event.getAction();final int keyCode = event.getKeyCode();if (action == KeyEvent.ACTION_DOWN) {return onKeyDown(keyCode, event);} else {return onKeyUp(keyCode, event);}}

进入onKeyDown

    boolean onKeyDown(int keyCode, KeyEvent event) {/* ***************************************************************************** HOW TO DECIDE WHERE YOUR KEY HANDLING GOES.* See the comment in PhoneWindow.onKeyDown* ****************************************************************************/final KeyEvent.DispatcherState dispatcher = mView.getKeyDispatcherState();switch (keyCode) {case KeyEvent.KEYCODE_VOLUME_UP:case KeyEvent.KEYCODE_VOLUME_DOWN:case KeyEvent.KEYCODE_VOLUME_MUTE: {handleVolumeKeyEvent(event);return true;}。。。。。}

    private void handleVolumeKeyEvent(KeyEvent keyEvent) {getMediaSessionManager().dispatchVolumeKeyEventAsSystemService(keyEvent,AudioManager.USE_DEFAULT_STREAM_TYPE);}

调用MeidaSessionManager::dispatchVolumeKeyEventAsSystemService()–>MediaSessionService::dispatchVolumeKeyEvent()

     /*将音量按钮事件分派给其中一个已注册的侦听器。如果有一个音量键长按侦听器，并且没有活动的全局优先级会话，长按将被发送到长按侦听器，而不是调整音量。如果没有注册长按监听器、没有活动的全局优先级会话，则进行音量调节*/@Overridepublic void dispatchVolumeKeyEvent(String packageName, boolean asSystemService,KeyEvent keyEvent, int stream, boolean musicOnly) {......try {synchronized (mLock) {//如果没有注册长按监听器，则调用dispatchVolumeKeyEventLocked进行音量调节。if (isGlobalPriorityActiveLocked()|| mCurrentFullUserRecord.mOnVolumeKeyLongPressListener == null) {dispatchVolumeKeyEventLocked(packageName, pid, uid, asSystemService,keyEvent, stream, musicOnly);} else {// TODO: Consider the case when both volume up and down keys are pressed//       at the same time.if (keyEvent.getAction() == KeyEvent.ACTION_DOWN) {if (keyEvent.getRepeatCount() == 0) {// Keeps the copy of the KeyEvent because it can be reused.mCurrentFullUserRecord.mInitialDownVolumeKeyEvent =KeyEvent.obtain(keyEvent);mCurrentFullUserRecord.mInitialDownVolumeStream = stream;mCurrentFullUserRecord.mInitialDownMusicOnly = musicOnly;mHandler.sendMessageDelayed(mHandler.obtainMessage(MessageHandler.MSG_VOLUME_INITIAL_DOWN,mCurrentFullUserRecord.mFullUserId, 0),mLongPressTimeout);}if (keyEvent.getRepeatCount() > 0 || keyEvent.isLongPress()) {mHandler.removeMessages(MessageHandler.MSG_VOLUME_INITIAL_DOWN);if (mCurrentFullUserRecord.mInitialDownVolumeKeyEvent != null) {dispatchVolumeKeyLongPressLocked(mCurrentFullUserRecord.mInitialDownVolumeKeyEvent);// Mark that the key is already handled.mCurrentFullUserRecord.mInitialDownVolumeKeyEvent = null;}dispatchVolumeKeyLongPressLocked(keyEvent);}} else { // if up......}

继续dispatchVolumeKeyEventLocked()–>dispatchAdjustVolumeLocked()

private void dispatchAdjustVolumeLocked(String packageName, int pid, int uid,boolean asSystemService, int suggestedStream, int direction, int flags) {MediaSessionRecord session = isGlobalPriorityActiveLocked() ? mGlobalPrioritySession: mCurrentFullUserRecord.mPriorityStack.getDefaultVolumeSession();boolean preferSuggestedStream = false;if (isValidLocalStreamType(suggestedStream)&& AudioSystem.isStreamActive(suggestedStream, 0)) {preferSuggestedStream = true;}if (session == null || preferSuggestedStream) {// Execute mAudioService.adjustSuggestedStreamVolume() on// handler thread of MediaSessionService.// This will release the MediaSessionService.mLock sooner and avoid// a potential deadlock between MediaSessionService.mLock and// ActivityManagerService lock.mHandler.post(new Runnable() {@Overridepublic void run() {try {String packageName = getContext().getOpPackageName();mAudioService.adjustSuggestedStreamVolume(direction, suggestedStream,flags, packageName, TAG);} }});} else {session.adjustVolume(packageName, pid, uid, null, asSystemService,direction, flags, true);}}

两种情况，一种调用mAudioService.adjustSuggestedStreamVolume()，一种调用session.adjustVolume()。这里以adjustSuggestedStreamVolume()为例。

AudioService音量控制流程

adjustSuggestedStreamVolume 过渡到adjustStreamVolume，进入音量设置的主要流程，主要对流类型，设备，声音设备状态，步进大小进行判断处理，另外蓝牙设备音量和主设备音量进行了控制，最后通过mVolumePanel刷新界面音量显示，并且广播通过上层应用。

protected void adjustStreamVolume(int streamType, int direction, int flags,String callingPackage, String caller, int uid) {。。。。。
if (adjustVolume && (direction != AudioManager.ADJUST_SAME)) {mAudioHandler.removeMessages(MSG_UNMUTE_STREAM);if (isMuteAdjust) {boolean state;if (direction == AudioManager.ADJUST_TOGGLE_MUTE) {state = !streamState.mIsMuted;} else {state = direction == AudioManager.ADJUST_MUTE;}if (streamTypeAlias == AudioSystem.STREAM_MUSIC) {setSystemAudioMute(state);}for (int stream = 0; stream < mStreamStates.length; stream++) {if (streamTypeAlias == mStreamVolumeAlias[stream]) {if (!(readCameraSoundForced()&& (mStreamStates[stream].getStreamType()== AudioSystem.STREAM_SYSTEM_ENFORCED))) {mStreamStates[stream].mute(state);}}}} else if ((direction == AudioManager.ADJUST_RAISE) &&!checkSafeMediaVolume(streamTypeAlias, aliasIndex + step, device)) {Log.e(TAG, "adjustStreamVolume() safe volume index = " + oldIndex);mVolumeController.postDisplaySafeVolumeWarning(flags);} else if (streamState.adjustIndex(direction * step, device, caller)|| streamState.mIsMuted) {// Post message to set system volume (it in turn will post a// message to persist).if (streamState.mIsMuted) {// Unmute the stream if it was previously mutedif (direction == AudioManager.ADJUST_RAISE) {// unmute immediately for volume upstreamState.mute(false);} else if (direction == AudioManager.ADJUST_LOWER) {if (mIsSingleVolume) {sendMsg(mAudioHandler, MSG_UNMUTE_STREAM, SENDMSG_QUEUE,streamTypeAlias, flags, null, UNMUTE_STREAM_DELAY);}}}//发送MSG_SET_DEVICE_VOLUME消息去设置系统音量,在handleMessage()被处理sendMsg(mAudioHandler,MSG_SET_DEVICE_VOLUME,SENDMSG_QUEUE,device,0,streamState,0);}int newIndex = mStreamStates[streamType].getIndex(device);// Check if volume update should be send to AVRCP//蓝牙音量的控制if (streamTypeAlias == AudioSystem.STREAM_MUSIC &&(device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 &&(flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) == 0) {synchronized (mA2dpAvrcpLock) {if (mA2dp != null && mAvrcpAbsVolSupported) {mA2dp.setAvrcpAbsoluteVolume(newIndex / 10);}}}// Check if volume update should be send to Hearing Aidif ((device & AudioSystem.DEVICE_OUT_HEARING_AID) != 0) {setHearingAidVolume(newIndex, streamType);}// Check if volume update should be sent to Hdmi system audio.//与HDMI输出相关if (streamTypeAlias == AudioSystem.STREAM_MUSIC) {setSystemAudioVolume(oldIndex, newIndex, getStreamMaxVolume(streamType), flags);}if (mHdmiManager != null) {......}}int index = mStreamStates[streamType].getIndex(device);//UI更新系统音量sendVolumeUpdate(streamType, oldIndex, index, flags);}

蓝牙音量的控制

由上可知，如果当前连接了蓝牙也将对音量进行控制，mA2dp.adjustAvrcpAbsoluteVolume，暂不分析。

音频处理设置

音频处理由AudioHandler来进行，adjustStreamVolume做完相关处理后，通过sendMsg发送音量变化消息MSG_SET_DEVICE_VOLUME进入AudioHandler.handleMessage调用AudioHandler.setDeviceVolume

private void setDeviceVolume(VolumeStreamState streamState, int device) {synchronized (VolumeStreamState.class) {// Apply volumestreamState.applyDeviceVolume_syncVSS(device);// Apply change to all streams using this one as aliasint numStreamTypes = AudioSystem.getNumStreamTypes();for (int streamType = numStreamTypes - 1; streamType >= 0; streamType--) {if (streamType != streamState.mStreamType &&mStreamVolumeAlias[streamType] == streamState.mStreamType) {// Make sure volume is also maxed out on A2DP device for aliased stream// that may have a different device selectedint streamDevice = getDeviceForStream(streamType);if ((device != streamDevice) && mAvrcpAbsVolSupported &&((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0)) {mStreamStates[streamType].applyDeviceVolume_syncVSS(device);}mStreamStates[streamType].applyDeviceVolume_syncVSS(streamDevice);}}}// Post a persist volume msgsendMsg(mAudioHandler,MSG_PERSIST_VOLUME,SENDMSG_QUEUE,device,0,streamState,PERSIST_DELAY);}

VolumeStreamState.applyDeviceVolume_syncVSS设置设备音量

// must be called while synchronized VolumeStreamState.classpublic void applyDeviceVolume_syncVSS(int device) {int index;if (mIsMuted) {index = 0;} else if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) != 0 && mAvrcpAbsVolSupported) {index = getAbsoluteVolumeIndex((getIndex(device) + 5)/10);} else if ((device & mFullVolumeDevices) != 0) {index = (mIndexMax + 5)/10;} else if ((device & AudioSystem.DEVICE_OUT_HEARING_AID) != 0) {index = (mIndexMax + 5)/10;} else {index = (getIndex(device) + 5)/10;}AudioSystem.setStreamVolumeIndex(mStreamType, index, device);}

接着发送MSG_PERSIST_VOLUME消息通过handleMessage进入persistVolume，最终调用System.putIntForUser将用户设置的内容设置到Settings.system中。

AudioSystem调节音量

applyDeviceVolume处理完，AudioSystem就开始接着往下设置setStreamVolumeIndex，通过JNI调用到AudioSystem.cpp中setStreamVolumeIndex()。


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);
}

获取去音频策略服务(AudioPolicyService.cpp)，进行设置
AudioPolicyService::setStreamVolumeIndex()–>AudioPolicyManager::setStreamVolumeIndex()