Android 音频源码分析——音量调节流程
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源码分析基于android9.0
一、声音类型
对于大多数手机用户来说，操作手机音量按键可以看到，声音类型分为四种：媒体、铃声、闹钟、通话，但是其系统内部则分为十几种类型。
声⾳类型用来区分不同播放用途及播放设备，包含11中类型
定义在 frameworks/base/media/java/android/media/Audiosystem.java中
/** Used to identify the default audio stream volume */
public static final int STREAM_DEFAULT = -1;
/** Used to identify the volume of audio streams for phone calls */
public static final int STREAM_VOICE_CALL = 0;
/** Used to identify the volume of audio streams for system sounds */
public static final int STREAM_SYSTEM = 1;
/** Used to identify the volume of audio streams for the phone ring and message alerts */
public static final int STREAM_RING = 2;
/** Used to identify the volume of audio streams for music playback */
public static final int STREAM_MUSIC = 3;
/** Used to identify the volume of audio streams for alarms */
public static final int STREAM_ALARM = 4;
/** Used to identify the volume of audio streams for notifications */
public static final int STREAM_NOTIFICATION = 5;
/** Used to identify the volume of audio streams for phone calls when connected on bluetooth */
public static final int STREAM_BLUETOOTH_SCO = 6;
/** Used to identify the volume of audio streams for enforced system sounds in certain
* countries (e.g camera in Japan) */
public static final int STREAM_SYSTEM_ENFORCED = 7;
/** Used to identify the volume of audio streams for DTMF tones */
public static final int STREAM_DTMF = 8;
/** Used to identify the volume of audio streams exclusively transmitted through the
* speaker (TTS) of the device */
public static final int STREAM_TTS = 9;
/** Used to identify the volume of audio streams for accessibility prompts */
public static final int STREAM_ACCESSIBILITY = 10;
虽然是11种类型，但许多是使用相同的音量配置。
在 frameworks/base/services/core/java/com/android/server/audio/AudioService.java
定义声音类型的具体使用类型，通过调节几个类型，从而控制所有的声音的音量。
private final int[] STREAM_VOLUME_ALIAS_DEFAULT = new int[]
AudioSystem.STREAM_VOICE_CALL, // STREAM_VOICE_CALL
AudioSystem.STREAM_RING, // STREAM_SYSTEM
AudioSystem.STREAM_RING, // STREAM_RING
AudioSystem.STREAM_MUSIC, // STREAM_MUSIC
AudioSystem.STREAM_ALARM, // STREAM_ALARM
AudioSystem.STREAM_RING, // STREAM_NOTIFICATION
AudioSystem.STREAM_BLUETOOTH_SCO, // STREAM_BLUETOOTH_SCO
AudioSystem.STREAM_RING, // STREAM_SYSTEM_ENFORCED
AudioSystem.STREAM_RING, // STREAM_DTMF
AudioSystem.STREAM_MUSIC, // STREAM_TTS
AudioSystem.STREAM_MUSIC // STREAM_ACCESSIBILITY
;
二、音量调节
Android调节音量主要有三种方式：
- 系统音量按键调节，framework调用AudioService接口
- 应用层通过AudioManager接口调节；
adjustStreamVolume 和setStreamVolume等 - AudioTrack调节音量，使用setVolume接口；
流程图如下：
这里分析下系统音量按键调节流程
framework层调节
PhoneWindowManager可以管理系统的一些按键事件：home键、返回键、Menu键、音量键等。
它接收到音量加减事件，如下函数：
private void dispatchDirectAudioEvent(KeyEvent event)
if (event.getAction() != KeyEvent.ACTION_DOWN)
return;
int keyCode = event.getKeyCode();
int flags = AudioManager.FLAG_SHOW_UI | AudioManager.FLAG_PLAY_SOUND
| AudioManager.FLAG_FROM_KEY;
String pkgName = mContext.getOpPackageName();
switch (keyCode)
case KeyEvent.KEYCODE_VOLUME_UP:
try
getAudioService().adjustSuggestedStreamVolume(AudioManager.ADJUST_RAISE,
AudioManager.USE_DEFAULT_STREAM_TYPE, flags, pkgName, TAG);
catch (Exception e)
Log.e(TAG, "Error dispatching volume up in dispatchTvAudioEvent.", e);
break;
case KeyEvent.KEYCODE_VOLUME_DOWN:
try
getAudioService().adjustSuggestedStreamVolume(AudioManager.ADJUST_LOWER,
AudioManager.USE_DEFAULT_STREAM_TYPE, flags, pkgName, TAG);
catch (Exception e)
Log.e(TAG, "Error dispatching volume down in dispatchTvAudioEvent.", e);
break;
case KeyEvent.KEYCODE_VOLUME_MUTE:
try
if (event.getRepeatCount() == 0)
getAudioService().adjustSuggestedStreamVolume(
AudioManager.ADJUST_TOGGLE_MUTE,
AudioManager.USE_DEFAULT_STREAM_TYPE, flags, pkgName, TAG);
catch (Exception e)
Log.e(TAG, "Error dispatching mute in dispatchTvAudioEvent.", e);
break;
对于音量加减都会调用getAudioService().adjustSuggestedStreamVolume，只是参数不同区分是加还是减。getAudioService获取AudioService,调用其接口调节。
AudioService
public void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
String callingPackage, String caller)
final IAudioPolicyCallback extVolCtlr;
synchronized (mExtVolumeControllerLock)
extVolCtlr = mExtVolumeController;
if (extVolCtlr != null)
sendMsg(mAudioHandler, MSG_NOTIFY_VOL_EVENT, SENDMSG_QUEUE,
direction, 0 /*ignored*/,
extVolCtlr, 0 /*delay*/);
else
adjustSuggestedStreamVolume(direction, suggestedStreamType, flags, callingPackage,
caller, Binder.getCallingUid());
adjustSuggestedStreamVolume调用重载函数，参数不一致，新加了调用uid参数
private void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
String callingPackage, String caller, int uid)
final int streamType;
synchronized (mForceControlStreamLock)
// Request lock in case mVolumeControlStream is changed by other thread.
if (mUserSelectedVolumeControlStream) // implies mVolumeControlStream != -1
streamType = mVolumeControlStream;
else
final int maybeActiveStreamType = getActiveStreamType(suggestedStreamType);
final boolean activeForReal;
if (maybeActiveStreamType == AudioSystem.STREAM_RING
|| maybeActiveStreamType == AudioSystem.STREAM_NOTIFICATION)
activeForReal = wasStreamActiveRecently(maybeActiveStreamType, 0);
else
activeForReal = AudioSystem.isStreamActive(maybeActiveStreamType, 0);
if (activeForReal || mVolumeControlStream == -1)
streamType = maybeActiveStreamType;
else
streamType = mVolumeControlStream;
final boolean isMute = isMuteAdjust(direction);
ensureValidStreamType(streamType);
final int resolvedStream = mStreamVolumeAlias[streamType];
// Play sounds on STREAM_RING only.
if ((flags & AudioManager.FLAG_PLAY_SOUND) != 0 &&
resolvedStream != AudioSystem.STREAM_RING)
flags &= ~AudioManager.FLAG_PLAY_SOUND;
// For notifications/ring, show the ui before making any adjustments
// Don't suppress mute/unmute requests
if (mVolumeController.suppressAdjustment(resolvedStream, flags, isMute))
direction = 0;
flags &= ~AudioManager.FLAG_PLAY_SOUND;
flags &= ~AudioManager.FLAG_VIBRATE;
if (DEBUG_VOL) Log.d(TAG, "Volume controller suppressed adjustment");
adjustStreamVolume(streamType, direction, flags, callingPackage, caller, uid);
- streamType 获取当前要控制的流类型；
- resolvedStream 通过streamType转换为其对于的音频流类型别名；
- 对于通知和铃声类型，显示调节音量ui；
- 调用adjustStreamVolume；
接着看adjustStreamVolume
protected void adjustStreamVolume(int streamType, int direction, int flags,
String callingPackage, String caller, int uid)
//...
int streamTypeAlias = mStreamVolumeAlias[streamType];
VolumeStreamState streamState = mStreamStates[streamTypeAlias];
final int device = getDeviceForStream(streamTypeAlias);
int aliasIndex = streamState.getIndex(device);
boolean adjustVolume = true;
int step;
// skip a2dp absolute volume control request when the device
// is not an a2dp device
if ((device & AudioSystem.DEVICE_OUT_ALL_A2DP) == 0 &&
(flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) != 0)
return;
// If we are being called by the system (e.g. hardware keys) check for current user
// so we handle user restrictions correctly.
if (uid == android.os.Process.SYSTEM_UID)
uid = UserHandle.getUid(getCurrentUserId(), UserHandle.getAppId(uid));
if (mAppOps.noteOp(STREAM_VOLUME_OPS[streamTypeAlias], uid, callingPackage)
!= AppOpsManager.MODE_ALLOWED)
return;
// reset any pending volume command
synchronized (mSafeMediaVolumeState)
mPendingVolumeCommand = null;
flags &= ~AudioManager.FLAG_FIXED_VOLUME;
if ((streamTypeAlias == AudioSystem.STREAM_MUSIC) &&
((device & mFixedVolumeDevices) != 0))
flags |= AudioManager.FLAG_FIXED_VOLUME;
// Always toggle between max safe volume and 0 for fixed volume devices where safe
// volume is enforced, and max and 0 for the others.
// This is simulated by stepping by the full allowed volume range
if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE &&
(device & mSafeMediaVolumeDevices) != 0)
step = safeMediaVolumeIndex(device);
else
step = streamState.getMaxIndex();
if (aliasIndex != 0)
aliasIndex = step;
else
// convert one UI step (+/-1) into a number of internal units on the stream alias
step = rescaleIndex(10, streamType, streamTypeAlias);
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 muted
if (direction == AudioManager.ADJUST_RAISE)
// unmute immediately for volume up
streamState.mute(false);
else if (direction == AudioManager.ADJUST_LOWER)
if (mIsSingleVolume)
sendMsg(mAudioHandler, MSG_UNMUTE_STREAM, SENDMSG_QUEUE,
streamTypeAlias, flags, null, UNMUTE_STREAM_DELAY);
sendMsg(mAudioHandler,
MSG_SET_DEVICE_VOLUME,
SENDMSG_QUEUE,
device,
0,
streamState,
0);
//.......
int index = mStreamStates[streamType].getIndex(device);
sendVolumeUpdate(streamType, oldIndex, index, flags);
- streamTypeAlias 获取音频流类型别名；
- streamState获取该音频流 状态；device 获取对应音频设备；
- step 转换为音频流调节的单位；
- streamState.adjustIndex 调节音量值保存在VolumeStreamState中；
- 发送MSG_SET_DEVICE_VOLUME 消息，调节音量
MSG_SET_DEVICE_VOLUME 调用流程
AudioService.setDeviceVolume()
>>streamState.applyDeviceVolume_syncVSS(device);
>>AudioSystem.setStreamVolumeIndex(mStreamType, index, device);
>>android_media_AudioSystem_setStreamVolumeIndex(JNIEnv *env,
jobject thiz,
jint stream,
jint index,
jint device);
>>AudioSystem::setStreamVolumeIndex(static_cast <audio_stream_type_t>(stream),
index,
(audio_devices_t)device);
>>aps->setStreamVolumeIndex(stream, index, device);
>>AudioPolicyService::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device);
>>AudioPolicyManager::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
audioserver层调节
这里接着看 AudioPolicyManager::setStreamVolumeIndex
status_t AudioPolicyManager::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
// VOICE_CALL stream has minVolumeIndex > 0 but can be muted directly by an
// app that has MODIFY_PHONE_STATE permission.
if (((index < mVolumeCurves->getVolumeIndexMin(stream)) &&
!(stream == AUDIO_STREAM_VOICE_CALL && index == 0)) ||
(index > mVolumeCurves->getVolumeIndexMax(stream)))
return BAD_VALUE;
if (!audio_is_output_device(device))
return BAD_VALUE;
// Force max volume if stream cannot be muted
if (!mVolumeCurves->canBeMuted(stream)) index = mVolumeCurves->getVolumeIndexMax(stream);
// update other private stream volumes which follow this one
for (int curStream = 0; curStream < AUDIO_STREAM_FOR_POLICY_CNT; curStream++)
if (!streamsMatchForvolume(stream, (audio_stream_type_t)curStream))
continue;
mVolumeCurves->addCurrentVolumeIndex((audio_stream_type_t)curStream, device, index);
// 更新符合以下条件的所有输出和流的音量:
// -请求的流（或与音量控制匹配的流）在输出中处于活动状态
// -与该流相对应的策略选择的设备（一个或多个）,包括请求的设备
// -对于非默认请求的设备，输出中当前选择的设备是请求的设备或策略选择的设备之一
// - 对于默认的请求设备（AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME），
// 仅当当前所选设备不存在特定设备音量值时，才应用音量。
status_t status = NO_ERROR;
for (size_t i = 0; i < mOutputs.size(); i++)
sp<SwAudioOutputDescriptor> desc = mOutputs.valueAt(i);
audio_devices_t curDevice = Volume::getDeviceForVolume(desc->device());
for (int curStream = 0; curStream < AUDIO_STREAM_FOR_POLICY_CNT; curStream++)
if (!streamsMatchForvolume(stream, (audio_stream_type_t)curStream))
continue;
if (!(desc->isStreamActive((audio_stream_type_t)curStream) ||
(isInCall() && (curStream == AUDIO_STREAM_VOICE_CALL))))
continue;
routing_strategy curStrategy = getStrategy((audio_stream_type_t)curStream);
audio_devices_t curStreamDevice = Volume::getDeviceForVolume(getDeviceForStrategy(
curStrategy, false /*fromCache*/));
if ((device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME) &&
((curStreamDevice & device) == 0))
continue;
bool applyVolume;
if (device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME)
curStreamDevice |= device;
applyVolume = (curDevice & curStreamDevice) != 0;
else
applyVolume = !mVolumeCurves->hasVolumeIndexForDevice(
stream, curStreamDevice);
if (applyVolume)
status_t volStatus =
checkAndSetVolume((audio_stream_type_t)curStream, index, desc, curDevice,
(stream == AUDIO_STREAM_SYSTEM) ? TOUCH_SOUND_FIXED_DELAY_MS : 0);
if (volStatus != NO_ERROR)
status = volStatus;
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