Methods for adjusting volume provided by the core Android system
The core Android system provides a variety of methods for adjusting volume, which mainly include the following.
- As we can see in the process of adjusting the volume in Android Automotive
CarAudioService, the volume is finally set directly for the device throughCarAudioDeviceInfo(packages/services/Car/service/src/com/android/car/audio/CarAudioDeviceInfo.java)AudioManager:
// Input is in millibels
void setCurrentGain(int gainInMillibels) {
// Clamp the incoming value to our valid range. Out of range values ARE legal input
if (gainInMillibels < mMinGain) {
gainInMillibels = mMinGain;
} else if (gainInMillibels > mMaxGain) {
gainInMillibels = mMaxGain;
}
// Push the new gain value down to our underlying port which will cause it to show up
// at the HAL.
AudioGain audioGain = getAudioGain();
if (audioGain == null) {
Slog.e(CarLog.TAG_AUDIO, "getAudioGain() returned null.");
return;
}
// size of gain values is 1 in MODE_JOINT
AudioGainConfig audioGainConfig = audioGain.buildConfig(
AudioGain.MODE_JOINT,
audioGain.channelMask(),
new int[] { gainInMillibels },
0);
if (audioGainConfig == null) {
Slog.e(CarLog.TAG_AUDIO, "Failed to construct AudioGainConfig");
return;
}
int r = AudioManager.setAudioPortGain(getAudioDevicePort(), audioGainConfig);
if (r == AudioManager.SUCCESS) {
// Since we can't query for the gain on a device port later,
// we have to remember what we asked for
mCurrentGain = gainInMillibels;
} else {
Slog.e(CarLog.TAG_AUDIO, "Failed to setAudioPortGain: " + r);
}
}
The method seen here AudioManagercan setAudioPortGain(getAudioDevicePort(), audioGainConfig)be used to adjust the volume of a specific device. In AudioManager, the implementation of this method ( frameworks/base/media/java/android/media/AudioManager.java ) is:
/**
* Set the gain on the specified AudioPort. The AudioGainConfig config is build by
* AudioGain.buildConfig()
* @hide
*/
public static int setAudioPortGain(AudioPort port, AudioGainConfig gain) {
if (port == null || gain == null) {
return ERROR_BAD_VALUE;
}
AudioPortConfig activeConfig = port.activeConfig();
AudioPortConfig config = new AudioPortConfig(port, activeConfig.samplingRate(),
activeConfig.channelMask(), activeConfig.format(), gain);
config.mConfigMask = AudioPortConfig.GAIN;
return AudioSystem.setAudioPortConfig(config);
}
AudioManagerThe setAudioPortGain(getAudioDevicePort(), audioGainConfig)method sets the volume for the device through AudioSystemthe static method , which is declared in frameworks/base/media/java/android/media/AudioSystem.java and finally defined in frameworks/base/core/jni/android_media_AudioSystem.cpp JNI native layer methods:setAudioPortConfig(config)AudioSystem.setAudioPortConfig(config)
static jint
android_media_AudioSystem_setAudioPortConfig(JNIEnv *env, jobject clazz,
jobject jAudioPortConfig)
{
ALOGV("setAudioPortConfig");
if (jAudioPortConfig == NULL) {
return AUDIO_JAVA_BAD_VALUE;
}
if (!env->IsInstanceOf(jAudioPortConfig, gAudioPortConfigClass)) {
return AUDIO_JAVA_BAD_VALUE;
}
struct audio_port_config nAudioPortConfig = {};
jint jStatus = convertAudioPortConfigToNative(env, &nAudioPortConfig, jAudioPortConfig, true);
if (jStatus != AUDIO_JAVA_SUCCESS) {
return jStatus;
}
status_t status = AudioSystem::setAudioPortConfig(&nAudioPortConfig);
ALOGV("AudioSystem::setAudioPortConfig() returned %d", status);
jStatus = nativeToJavaStatus(status);
return jStatus;
}
- App can
AudioManageradjustSTREAM_TYPEthe volume of a certain through , such as:
private boolean setStreamVolume(int volume) {
Logging.d(TAG, "setStreamVolume(" + volume + ")");
assertTrue(audioManager != null);
if (isVolumeFixed()) {
Logging.e(TAG, "The device implements a fixed volume policy.");
return false;
}
audioManager.setStreamVolume(AudioManager.STREAM_VOICE_CALL, volume, 0);
return true;
}
setStreamVolume()The implementation of the method seen here AudioManageris as follows:
/**
* Sets the volume index for a particular stream.
* <p>This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
* <p>From N onward, volume adjustments that would toggle Do Not Disturb are not allowed unless
* the app has been granted Do Not Disturb Access.
* See {@link NotificationManager#isNotificationPolicyAccessGranted()}.
* @param streamType The stream whose volume index should be set.
* @param index The volume index to set. See
* {@link #getStreamMaxVolume(int)} for the largest valid value.
* @param flags One or more flags.
* @see #getStreamMaxVolume(int)
* @see #getStreamVolume(int)
* @see #isVolumeFixed()
* @throws SecurityException if the volume change triggers a Do Not Disturb change
* and the caller is not granted notification policy access.
*/
public void setStreamVolume(int streamType, int index, int flags) {
final IAudioService service = getService();
try {
service.setStreamVolume(streamType, index, flags, getContext().getOpPackageName());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AudioManagerTo increase or decrease a specific stream type in a single stepadjustStreamVolume():
/**
* Adjusts the volume of a particular stream by one step in a direction.
* <p>
* This method should only be used by applications that replace the platform-wide
* management of audio settings or the main telephony application.
* <p>This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
* <p>From N onward, ringer mode adjustments that would toggle Do Not Disturb are not allowed
* unless the app has been granted Do Not Disturb Access.
* See {@link NotificationManager#isNotificationPolicyAccessGranted()}.
*
* @param streamType The stream type to adjust. One of {@link #STREAM_VOICE_CALL},
* {@link #STREAM_SYSTEM}, {@link #STREAM_RING}, {@link #STREAM_MUSIC},
* {@link #STREAM_ALARM} or {@link #STREAM_ACCESSIBILITY}.
* @param direction The direction to adjust the volume. One of
* {@link #ADJUST_LOWER}, {@link #ADJUST_RAISE}, or
* {@link #ADJUST_SAME}.
* @param flags One or more flags.
* @see #adjustVolume(int, int)
* @see #setStreamVolume(int, int, int)
* @throws SecurityException if the adjustment triggers a Do Not Disturb change
* and the caller is not granted notification policy access.
*/
public void adjustStreamVolume(int streamType, int direction, int flags) {
final IAudioService service = getService();
try {
service.adjustStreamVolume(streamType, direction, flags,
getContext().getOpPackageName());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AudioManagerto adjust the volume of the most relevant stream inadjustVolume()andadjustSuggestedStreamVolume():
/**
* Adjusts the volume of the most relevant stream. For example, if a call is
* active, it will have the highest priority regardless of if the in-call
* screen is showing. Another example, if music is playing in the background
* and a call is not active, the music stream will be adjusted.
* <p>
* This method should only be used by applications that replace the
* platform-wide management of audio settings or the main telephony
* application.
* <p>
* This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
*
* @param direction The direction to adjust the volume. One of
* {@link #ADJUST_LOWER}, {@link #ADJUST_RAISE},
* {@link #ADJUST_SAME}, {@link #ADJUST_MUTE},
* {@link #ADJUST_UNMUTE}, or {@link #ADJUST_TOGGLE_MUTE}.
* @param flags One or more flags.
* @see #adjustSuggestedStreamVolume(int, int, int)
* @see #adjustStreamVolume(int, int, int)
* @see #setStreamVolume(int, int, int)
* @see #isVolumeFixed()
*/
public void adjustVolume(int direction, int flags) {
MediaSessionLegacyHelper helper = MediaSessionLegacyHelper.getHelper(getContext());
helper.sendAdjustVolumeBy(USE_DEFAULT_STREAM_TYPE, direction, flags);
}
/**
* Adjusts the volume of the most relevant stream, or the given fallback
* stream.
* <p>
* This method should only be used by applications that replace the
* platform-wide management of audio settings or the main telephony
* application.
* <p>
* This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
*
* @param direction The direction to adjust the volume. One of
* {@link #ADJUST_LOWER}, {@link #ADJUST_RAISE},
* {@link #ADJUST_SAME}, {@link #ADJUST_MUTE},
* {@link #ADJUST_UNMUTE}, or {@link #ADJUST_TOGGLE_MUTE}.
* @param suggestedStreamType The stream type that will be used if there
* isn't a relevant stream. {@link #USE_DEFAULT_STREAM_TYPE} is
* valid here.
* @param flags One or more flags.
* @see #adjustVolume(int, int)
* @see #adjustStreamVolume(int, int, int)
* @see #setStreamVolume(int, int, int)
* @see #isVolumeFixed()
*/
public void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags) {
MediaSessionLegacyHelper helper = MediaSessionLegacyHelper.getHelper(getContext());
helper.sendAdjustVolumeBy(suggestedStreamType, direction, flags);
}
These two methods ultimately adjust the volume through the media session service ( frameworks/base/media/java/android/media/session/MediaSessionLegacyHelper.java ):
private MediaSessionLegacyHelper(Context context) {
mContext = context;
mSessionManager = (MediaSessionManager) context
.getSystemService(Context.MEDIA_SESSION_SERVICE);
}
public void sendAdjustVolumeBy(int suggestedStream, int delta, int flags) {
mSessionManager.dispatchAdjustVolume(suggestedStream, delta, flags);
if (DEBUG) {
Log.d(TAG, "dispatched volume adjustment");
}
}
AudioManagerAudioAttributesto set the volume for a specificsetVolumeIndexForAttributes().
/**
* Sets the volume index for a particular {@link AudioAttributes}.
* @param attr The {@link AudioAttributes} whose volume index should be set.
* @param index The volume index to set. See
* {@link #getMaxVolumeIndexForAttributes(AudioAttributes)} for the largest valid value
* {@link #getMinVolumeIndexForAttributes(AudioAttributes)} for the lowest valid value.
* @param flags One or more flags.
* @see #getMaxVolumeIndexForAttributes(AudioAttributes)
* @see #getMinVolumeIndexForAttributes(AudioAttributes)
* @see #isVolumeFixed()
* @hide
*/
@SystemApi
@RequiresPermission(android.Manifest.permission.MODIFY_AUDIO_ROUTING)
public void setVolumeIndexForAttributes(@NonNull AudioAttributes attr, int index, int flags) {
Preconditions.checkNotNull(attr, "attr must not be null");
final IAudioService service = getService();
try {
service.setVolumeIndexForAttributes(attr, index, flags,
getContext().getOpPackageName());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AudioManagerAdjusts the volume of the most relevant stream and checks whether the caller has the necessary permissions based on the provided component name, uid and pid valuesadjustSuggestedStreamVolumeForUid().
/**
* Adjusts the volume of the most relevant stream, or the given fallback
* stream.
* <p>
* This method should only be used by applications that replace the
* platform-wide management of audio settings or the main telephony
* application.
* <p>
* This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
* <p>This API checks if the caller has the necessary permissions based on the provided
* component name, uid, and pid values.
* See {@link #adjustSuggestedStreamVolume(int, int, int)}.
*
* @param suggestedStreamType The stream type that will be used if there
* isn't a relevant stream. {@link #USE_DEFAULT_STREAM_TYPE} is
* valid here.
* @param direction The direction to adjust the volume. One of
* {@link #ADJUST_LOWER}, {@link #ADJUST_RAISE},
* {@link #ADJUST_SAME}, {@link #ADJUST_MUTE},
* {@link #ADJUST_UNMUTE}, or {@link #ADJUST_TOGGLE_MUTE}.
* @param flags One or more flags.
* @param packageName the package name of client application
* @param uid the uid of client application
* @param pid the pid of client application
* @param targetSdkVersion the target sdk version of client application
* @see #adjustVolume(int, int)
* @see #adjustStreamVolume(int, int, int)
* @see #setStreamVolume(int, int, int)
* @see #isVolumeFixed()
*
* @hide
*/
@SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
public void adjustSuggestedStreamVolumeForUid(int suggestedStreamType, int direction, int flags,
@NonNull String packageName, int uid, int pid, int targetSdkVersion) {
try {
getService().adjustSuggestedStreamVolumeForUid(suggestedStreamType, direction, flags,
packageName, uid, pid, UserHandle.getUserHandleForUid(uid), targetSdkVersion);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AudioManagerStep by step to increase or decrease the volume of a specific stream type, and check whether the caller has the necessary permissions based on the provided component name, uid and pid valuesadjustStreamVolumeForUid():
/**
* Adjusts the volume of a particular stream by one step in a direction.
* <p>
* This method should only be used by applications that replace the platform-wide
* management of audio settings or the main telephony application.
* <p>This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
* <p>From N onward, ringer mode adjustments that would toggle Do Not Disturb are not allowed
* unless the app has been granted Do Not Disturb Access.
* See {@link NotificationManager#isNotificationPolicyAccessGranted()}.
* <p>This API checks if the caller has the necessary permissions based on the provided
* component name, uid, and pid values.
* See {@link #adjustStreamVolume(int, int, int)}.
*
* @param streamType The stream type to adjust. One of {@link #STREAM_VOICE_CALL},
* {@link #STREAM_SYSTEM}, {@link #STREAM_RING}, {@link #STREAM_MUSIC},
* {@link #STREAM_ALARM} or {@link #STREAM_ACCESSIBILITY}.
* @param direction The direction to adjust the volume. One of
* {@link #ADJUST_LOWER}, {@link #ADJUST_RAISE}, or
* {@link #ADJUST_SAME}.
* @param flags One or more flags.
* @param packageName the package name of client application
* @param uid the uid of client application
* @param pid the pid of client application
* @param targetSdkVersion the target sdk version of client application
* @see #adjustVolume(int, int)
* @see #setStreamVolume(int, int, int)
* @throws SecurityException if the adjustment triggers a Do Not Disturb change
* and the caller is not granted notification policy access.
*
* @hide
*/
@SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
public void adjustStreamVolumeForUid(int streamType, int direction, int flags,
@NonNull String packageName, int uid, int pid, int targetSdkVersion) {
try {
getService().adjustStreamVolumeForUid(streamType, direction, flags, packageName, uid,
pid, UserHandle.getUserHandleForUid(uid), targetSdkVersion);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
AudioManagerAdjustSTREAM_TYPEthe volume of a certain , and check whether the caller has the necessary permissions based on the provided component name, uid and pid valuessetStreamVolumeForUid():
/**
* Sets the volume index for a particular stream.
* <p>This method has no effect if the device implements a fixed volume policy
* as indicated by {@link #isVolumeFixed()}.
* <p>From N onward, volume adjustments that would toggle Do Not Disturb are not allowed unless
* the app has been granted Do Not Disturb Access.
* See {@link NotificationManager#isNotificationPolicyAccessGranted()}.
* <p>This API checks if the caller has the necessary permissions based on the provided
* component name, uid, and pid values.
* See {@link #setStreamVolume(int, int, int)}.
*
* @param streamType The stream whose volume index should be set.
* @param index The volume index to set. See
* {@link #getStreamMaxVolume(int)} for the largest valid value.
* @param flags One or more flags.
* @param packageName the package name of client application
* @param uid the uid of client application
* @param pid the pid of client application
* @param targetSdkVersion the target sdk version of client application
* @see #getStreamMaxVolume(int)
* @see #getStreamVolume(int)
* @see #isVolumeFixed()
* @throws SecurityException if the volume change triggers a Do Not Disturb change
* and the caller is not granted notification policy access.
*
* @hide
*/
@SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
public void setStreamVolumeForUid(int streamType, int index, int flags,
@NonNull String packageName, int uid, int pid, int targetSdkVersion) {
try {
getService().setStreamVolumeForUid(streamType, index, flags, packageName, uid, pid,
UserHandle.getUserHandleForUid(uid), targetSdkVersion);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
To sum up, the above methods mainly include the following functionally:
- Set the volume directly to the device;
- Adjust
STREAM_TYPEthe volume of a certain; - Increase or decrease the volume of specific stream types in a single step;
- Adjust the volume of the most relevant streams;
AudioAttributesSet the volume for a specific ;- Adjusts the volume of the most relevant stream and checks whether the caller has the necessary permissions based on the supplied component name, uid and pid values;
- Steps up or down the volume of a specific stream type, checking whether the caller has the necessary permissions based on the provided component name, uid, and pid values;
- Adjusts
STREAM_TYPEthe volume of an and checks whether the caller has the necessary permissions based on the supplied component name, uid and pid values.
AudioManagerIt is mainly the client proxy of the audio service running in system_server, but some of the encapsulated operations will also be completed directly through the media session service or audio policy service. Except for the 1st and 4th functions above, other functions are basically completed by calling the method of the same name of the audio service.
AudioServiceNext, let’s look at the implementation of the methods called above one by one .
- In
AudioService(frameworks/base/services/core/java/com/android/server/audio/AudioService.java), the methodAudioManagercorresponding to the method insetStreamVolume()is implemented as follows:
/** @see AudioManager#setStreamVolume(int, int, int)
* Part of service interface, check permissions here */
public void setStreamVolume(int streamType, int index, int flags, String callingPackage) {
if ((streamType == AudioManager.STREAM_ACCESSIBILITY) && !canChangeAccessibilityVolume()) {
Log.w(TAG, "Trying to call setStreamVolume() for a11y without"
+ " CHANGE_ACCESSIBILITY_VOLUME callingPackage=" + callingPackage);
return;
}
if ((streamType == AudioManager.STREAM_VOICE_CALL) && (index == 0)
&& (mContext.checkCallingOrSelfPermission(
android.Manifest.permission.MODIFY_PHONE_STATE)
!= PackageManager.PERMISSION_GRANTED)) {
Log.w(TAG, "Trying to call setStreamVolume() for STREAM_VOICE_CALL and index 0 without"
+ " MODIFY_PHONE_STATE callingPackage=" + callingPackage);
return;
}
if ((streamType == AudioManager.STREAM_ASSISTANT)
&& (mContext.checkCallingOrSelfPermission(
android.Manifest.permission.MODIFY_AUDIO_ROUTING)
!= PackageManager.PERMISSION_GRANTED)) {
Log.w(TAG, "Trying to call setStreamVolume() for STREAM_ASSISTANT without"
+ " MODIFY_AUDIO_ROUTING callingPackage=" + callingPackage);
return;
}
sVolumeLogger.log(new VolumeEvent(VolumeEvent.VOL_SET_STREAM_VOL, streamType,
index/*val1*/, flags/*val2*/, callingPackage));
setStreamVolume(streamType, index, flags, callingPackage, callingPackage,
Binder.getCallingUid(), callingOrSelfHasAudioSettingsPermission());
}
The process of performing this operation is roughly as follows:
(1). Ensure that the caller has sufficient authority to modify the volume of the stream type;
(2). Set the volume for the stream type.
This operation ultimately comes back to setting the volume for the stream type.
- Increase or decrease the volume of specific stream types in a single step
/** @see AudioManager#adjustStreamVolume(int, int, int)
* Part of service interface, check permissions here */
public void adjustStreamVolume(int streamType, int direction, int flags,
String callingPackage) {
if ((streamType == AudioManager.STREAM_ACCESSIBILITY) && !canChangeAccessibilityVolume()) {
Log.w(TAG, "Trying to call adjustStreamVolume() for a11y without"
+ "CHANGE_ACCESSIBILITY_VOLUME / callingPackage=" + callingPackage);
return;
}
sVolumeLogger.log(new VolumeEvent(VolumeEvent.VOL_ADJUST_STREAM_VOL, streamType,
direction/*val1*/, flags/*val2*/, callingPackage));
adjustStreamVolume(streamType, direction, flags, callingPackage, callingPackage,
Binder.getCallingUid(), Binder.getCallingPid(),
callingHasAudioSettingsPermission(), VOL_ADJUST_NORMAL);
}
The process of performing this operation is roughly as follows:
(1). Ensure that the caller has sufficient authority to modify the volume of the stream type;
(2). Adjust the volume of the stream type.
This operation ultimately comes back to adjusting the volume of the stream type.
-
The sum of adjusting the volume of the most relevant stream will take a detour through the media session service and eventually return to adjusting the volume of the stream type or setting the volume of the stream type
adjustVolume().adjustSuggestedStreamVolume() -
AudioAttributesSet the volume for a specific
/** @see AudioManager#setVolumeIndexForAttributes(attr, int, int) */
public void setVolumeIndexForAttributes(@NonNull AudioAttributes attr, int index, int flags,
String callingPackage) {
enforceModifyAudioRoutingPermission();
Objects.requireNonNull(attr, "attr must not be null");
final int volumeGroup = getVolumeGroupIdForAttributes(attr);
if (sVolumeGroupStates.indexOfKey(volumeGroup) < 0) {
Log.e(TAG, ": no volume group found for attributes " + attr.toString());
return;
}
final VolumeGroupState vgs = sVolumeGroupStates.get(volumeGroup);
sVolumeLogger.log(new VolumeEvent(VolumeEvent.VOL_SET_GROUP_VOL, attr, vgs.name(),
index/*val1*/, flags/*val2*/, callingPackage));
vgs.setVolumeIndex(index, flags);
// For legacy reason, propagate to all streams associated to this volume group
for (final int groupedStream : vgs.getLegacyStreamTypes()) {
try {
ensureValidStreamType(groupedStream);
} catch (IllegalArgumentException e) {
Log.d(TAG, "volume group " + volumeGroup + " has internal streams (" + groupedStream
+ "), do not change associated stream volume");
continue;
}
setStreamVolume(groupedStream, index, flags, callingPackage, callingPackage,
Binder.getCallingUid(), true /*hasModifyAudioSettings*/);
}
}
This process is roughly as follows:
(1). Ensure that the caller has sufficient authority to modify audio routing;
(2). Obtain the volume group based on the incoming AudioAttributes;
(3). Set the volume for the volume group itself;
(4). Set the volume for each member in the volume group A stream type sets the volume.
This operation ultimately comes back to setting the volume for the stream type.
- Adjusts the volume of the most relevant stream and checks whether the caller has the necessary permissions based on the supplied component name, uid and pid values
private void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
String callingPackage, String caller, int uid, int pid, boolean hasModifyAudioSettings,
int keyEventMode) {
if (DEBUG_VOL) Log.d(TAG, "adjustSuggestedStreamVolume() stream=" + suggestedStreamType
+ ", flags=" + flags + ", caller=" + caller
+ ", volControlStream=" + mVolumeControlStream
+ ", userSelect=" + mUserSelectedVolumeControlStream);
if (direction != AudioManager.ADJUST_SAME) {
sVolumeLogger.log(new VolumeEvent(VolumeEvent.VOL_ADJUST_SUGG_VOL, suggestedStreamType,
direction/*val1*/, flags/*val2*/, new StringBuilder(callingPackage)
.append("/").append(caller).append(" uid:").append(uid).toString()));
}
boolean hasExternalVolumeController = notifyExternalVolumeController(direction);
new MediaMetrics.Item(mMetricsId + "adjustSuggestedStreamVolume")
.setUid(Binder.getCallingUid())
.set(MediaMetrics.Property.CALLING_PACKAGE, callingPackage)
.set(MediaMetrics.Property.CLIENT_NAME, caller)
.set(MediaMetrics.Property.DIRECTION, direction > 0
? MediaMetrics.Value.UP : MediaMetrics.Value.DOWN)
.set(MediaMetrics.Property.EXTERNAL, hasExternalVolumeController
? MediaMetrics.Value.YES : MediaMetrics.Value.NO)
.set(MediaMetrics.Property.FLAGS, flags)
.record();
if (hasExternalVolumeController) {
return;
}
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 = mAudioSystem.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
// Don't suppress adjustments for single volume device
if (mVolumeController.suppressAdjustment(resolvedStream, flags, isMute)
&& !mIsSingleVolume) {
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, pid,
hasModifyAudioSettings, keyEventMode);
}
. . . . . .
/** @see AudioManager#adjustSuggestedStreamVolumeForUid(int, int, int, String, int, int, int) */
@Override
public void adjustSuggestedStreamVolumeForUid(int streamType, int direction, int flags,
@NonNull String packageName, int uid, int pid, UserHandle userHandle,
int targetSdkVersion) {
if (Binder.getCallingUid() != Process.SYSTEM_UID) {
throw new SecurityException("Should only be called from system process");
}
// direction and stream type swap here because the public
// adjustSuggested has a different order than the other methods.
adjustSuggestedStreamVolume(direction, streamType, flags, packageName, packageName,
uid, pid, hasAudioSettingsPermission(uid, pid), VOL_ADJUST_NORMAL);
}
The process of performing this operation is roughly as follows:
(1). Make sure the caller's UID is Process.SYSTEM_UID;
(2). Find the appropriate stream type;
(3). Adjust the volume of the stream type.
This operation ultimately comes back to adjusting the volume of the stream type.
- Steps up or down the volume of a specific stream type, checking whether the caller has the necessary permissions based on the provided component name, uid, and pid values;
/** @see AudioManager#adjustStreamVolumeForUid(int, int, int, String, int, int, int) */
@Override
public void adjustStreamVolumeForUid(int streamType, int direction, int flags,
@NonNull String packageName, int uid, int pid, UserHandle userHandle,
int targetSdkVersion) {
if (Binder.getCallingUid() != Process.SYSTEM_UID) {
throw new SecurityException("Should only be called from system process");
}
if (direction != AudioManager.ADJUST_SAME) {
sVolumeLogger.log(new VolumeEvent(VolumeEvent.VOL_ADJUST_VOL_UID, streamType,
direction/*val1*/, flags/*val2*/,
new StringBuilder(packageName).append(" uid:").append(uid)
.toString()));
}
adjustStreamVolume(streamType, direction, flags, packageName, packageName, uid, pid,
hasAudioSettingsPermission(uid, pid), VOL_ADJUST_NORMAL);
}
The process of performing this operation is roughly as follows:
(1). Make sure the caller's UID is Process.SYSTEM_UID;
(2). Adjust the volume of the stream type.
This operation ultimately comes back to adjusting the volume of the stream type.
- Adjusts
STREAM_TYPEthe volume of a and checks whether the caller has the necessary permissions based on the supplied component name, uid and pid values
/** @see AudioManager#setStreamVolumeForUid(int, int, int, String, int, int, int) */
@Override
public void setStreamVolumeForUid(int streamType, int index, int flags,
@NonNull String packageName, int uid, int pid, UserHandle userHandle,
int targetSdkVersion) {
if (Binder.getCallingUid() != Process.SYSTEM_UID) {
throw new SecurityException("Should only be called from system process");
}
setStreamVolume(streamType, index, flags, packageName, packageName, uid,
hasAudioSettingsPermission(uid, pid));
}
The process of performing this operation is roughly as follows:
(1). Make sure the caller's UID is Process.SYSTEM_UID;
(2). Set the volume for the stream type, and the incoming uid and pid are used to check permissions.
This operation ultimately comes back to setting the volume for the stream type.
In general, AudioManagerinterfaces other than those that directly adjust the volume of the device will eventually return to setting the volume for the stream type or adjusting the volume of the stream type. Here's a look at the process of setting the volume for stream type.
As can be seen from the above methods of adjusting the volume, Android Automotive's action of adjusting the volume intentionally adjusts the volume of the device directly in the Car service, without continuing to go through the audio service of the core Android system.
I won't follow the process of adjusting the volume of the stream type in depth here, but you can take a look at the process of setting the volume for the stream type.
Set volume for stream type
The method to set the volume for the stream type setStreamVolume()is defined as follows:
private void setStreamVolume(int streamType, int index, int flags, String callingPackage,
String caller, int uid, boolean hasModifyAudioSettings) {
if (DEBUG_VOL) {
Log.d(TAG, "setStreamVolume(stream=" + streamType+", index=" + index
+ ", calling=" + callingPackage + ")");
}
if (mUseFixedVolume) {
return;
}
ensureValidStreamType(streamType);
int streamTypeAlias = mStreamVolumeAlias[streamType];
VolumeStreamState streamState = mStreamStates[streamTypeAlias];
final int device = getDeviceForStream(streamType);
int oldIndex;
// skip a2dp absolute volume control request when the device
// is not an a2dp device
if (!AudioSystem.DEVICE_OUT_ALL_A2DP_SET.contains(device)
&& (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 (!checkNoteAppOp(STREAM_VOLUME_OPS[streamTypeAlias], uid, callingPackage)) {
return;
}
if (isAndroidNPlus(callingPackage)
&& wouldToggleZenMode(getNewRingerMode(streamTypeAlias, index, flags))
&& !mNm.isNotificationPolicyAccessGrantedForPackage(callingPackage)) {
throw new SecurityException("Not allowed to change Do Not Disturb state");
}
if (!volumeAdjustmentAllowedByDnd(streamTypeAlias, flags)) {
return;
}
synchronized (mSafeMediaVolumeStateLock) {
// reset any pending volume command
mPendingVolumeCommand = null;
oldIndex = streamState.getIndex(device);
index = rescaleIndex(index * 10, streamType, streamTypeAlias);
if (streamTypeAlias == AudioSystem.STREAM_MUSIC
&& AudioSystem.DEVICE_OUT_ALL_A2DP_SET.contains(device)
&& (flags & AudioManager.FLAG_BLUETOOTH_ABS_VOLUME) == 0) {
if (DEBUG_VOL) {
Log.d(TAG, "setStreamVolume postSetAvrcpAbsoluteVolumeIndex index=" + index
+ "stream=" + streamType);
}
mDeviceBroker.postSetAvrcpAbsoluteVolumeIndex(index / 10);
}
if (device == AudioSystem.DEVICE_OUT_HEARING_AID
&& streamType == getHearingAidStreamType()) {
Log.i(TAG, "setStreamVolume postSetHearingAidVolumeIndex index=" + index
+ " stream=" + streamType);
mDeviceBroker.postSetHearingAidVolumeIndex(index, streamType);
}
if (streamTypeAlias == AudioSystem.STREAM_MUSIC) {
setSystemAudioVolume(oldIndex, index, getStreamMaxVolume(streamType), flags);
}
flags &= ~AudioManager.FLAG_FIXED_VOLUME;
if (streamTypeAlias == AudioSystem.STREAM_MUSIC && isFixedVolumeDevice(device)) {
flags |= AudioManager.FLAG_FIXED_VOLUME;
// volume is either 0 or max allowed for fixed volume devices
if (index != 0) {
if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE &&
mSafeMediaVolumeDevices.contains(device)) {
index = safeMediaVolumeIndex(device);
} else {
index = streamState.getMaxIndex();
}
}
}
if (!checkSafeMediaVolume(streamTypeAlias, index, device)) {
mVolumeController.postDisplaySafeVolumeWarning(flags);
mPendingVolumeCommand = new StreamVolumeCommand(
streamType, index, flags, device);
} else {
onSetStreamVolume(streamType, index, flags, device, caller, hasModifyAudioSettings);
index = mStreamStates[streamType].getIndex(device);
}
}
synchronized (mHdmiClientLock) {
if (streamTypeAlias == AudioSystem.STREAM_MUSIC
&& (oldIndex != index)) {
maybeSendSystemAudioStatusCommand(false);
}
}
sendVolumeUpdate(streamType, oldIndex, index, flags, device);
}
This method first checks whether the fixed audio policy is configured to use mUseFixedVolume. This value comes from the configuration file: frameworks/base/core/res/res/values/config.xml :
mUseFixedVolume = mContext.getResources().getBoolean(
com.android.internal.R.bool.config_useFixedVolume);
This value can be overridden by a value defined specifically for the device. For example, for the car version of the simulator, the values defined in the device/generic/car/emulator/audio/overlay/frameworks/base/core/res/res/values/config.xml file override the values defined in the framework.
This is the main place where audio strategy is implemented.
AudioSystemThen get the device number ( frameworks/base/services/core/java/com/android/server/audio/AudioSystemAdapter.java ) according to the stream type :
public int getDevicesForStream(int stream) {
if (!ENABLE_GETDEVICES_STATS) {
return getDevicesForStreamImpl(stream);
}
mMethodCallCounter[METHOD_GETDEVICESFORSTREAM]++;
final long startTime = SystemClock.uptimeNanos();
final int res = getDevicesForStreamImpl(stream);
mMethodTimeNs[METHOD_GETDEVICESFORSTREAM] += SystemClock.uptimeNanos() - startTime;
return res;
}
private int getDevicesForStreamImpl(int stream) {
if (USE_CACHE_FOR_GETDEVICES) {
Integer res;
synchronized (mDevicesForStreamCache) {
res = mDevicesForStreamCache.get(stream);
if (res == null) {
res = AudioSystem.getDevicesForStream(stream);
mDevicesForStreamCache.put(stream, res);
if (DEBUG_CACHE) {
Log.d(TAG, mMethodNames[METHOD_GETDEVICESFORSTREAM]
+ streamDeviceToDebugString(stream, res));
}
return res;
}
// cache hit
mMethodCacheHit[METHOD_GETDEVICESFORSTREAM]++;
if (DEBUG_CACHE) {
final int real = AudioSystem.getDevicesForStream(stream);
if (res == real) {
Log.d(TAG, mMethodNames[METHOD_GETDEVICESFORSTREAM]
+ streamDeviceToDebugString(stream, res) + " CACHE");
} else {
Log.e(TAG, mMethodNames[METHOD_GETDEVICESFORSTREAM]
+ streamDeviceToDebugString(stream, res)
+ " CACHE ERROR real dev=0x" + Integer.toHexString(real));
}
}
}
return res;
}
// not using cache
return AudioSystem.getDevicesForStream(stream);
}
The call stack is as follows:
getDevicesForStreamImpl:164, AudioSystemAdapter (com.android.server.audio)
getDevicesForStream:151, AudioSystemAdapter (com.android.server.audio)
observeDevicesForStream_syncVSS:6838, AudioService$VolumeStreamState (com.android.server.audio)
getDevicesForStreamInt:6111, AudioService (com.android.server.audio)
getDeviceForStream:6063, AudioService (com.android.server.audio)
setStreamVolume:3576, AudioService (com.android.server.audio)
setStreamVolume:3327, AudioService (com.android.server.audio)
onTransact:1529, IAudioService$Stub (android.media)
execTransactInternal:1179, Binder (android.os)
execTransact:1143, Binder (android.os)
The device number obtained through AudioSystemmay contain multiple devices. Each specific device is represented by a binary digit in the device number here. At this time, the specific device needs to be selected according to priority from these devices. This process (frameworks / base/services/core/java/com/android/server/audio/AudioService.java ) as follows:
/** only public for mocking/spying, do not call outside of AudioService */
@VisibleForTesting
public int getDeviceForStream(int stream) {
int device = getDevicesForStreamInt(stream);
if ((device & (device - 1)) != 0) {
// Multiple device selection is either:
// - speaker + one other device: give priority to speaker in this case.
// - one A2DP device + another device: happens with duplicated output. In this case
// retain the device on the A2DP output as the other must not correspond to an active
// selection if not the speaker.
// - HDMI-CEC system audio mode only output: give priority to available item in order.
// FIXME: Haven't applied audio device type refactor to this API
// as it is going to be deprecated.
if ((device & AudioSystem.DEVICE_OUT_SPEAKER) != 0) {
device = AudioSystem.DEVICE_OUT_SPEAKER;
} else if ((device & AudioSystem.DEVICE_OUT_HDMI_ARC) != 0) {
// FIXME(b/184944421): DEVICE_OUT_HDMI_EARC has two bits set,
// so it must be handled correctly as it aliases
// with DEVICE_OUT_HDMI_ARC | DEVICE_OUT_EARPIECE.
device = AudioSystem.DEVICE_OUT_HDMI_ARC;
} else if ((device & AudioSystem.DEVICE_OUT_SPDIF) != 0) {
device = AudioSystem.DEVICE_OUT_SPDIF;
} else if ((device & AudioSystem.DEVICE_OUT_AUX_LINE) != 0) {
device = AudioSystem.DEVICE_OUT_AUX_LINE;
} else {
for (int deviceType : AudioSystem.DEVICE_OUT_ALL_A2DP_SET) {
if ((deviceType & device) == deviceType) {
return deviceType;
}
}
}
}
return device;
}
Then normalize the incoming volume value ( frameworks/base/services/core/java/com/android/server/audio/AudioService.java ):
private int rescaleIndex(int index, int srcStream, int dstStream) {
int srcRange = getIndexRange(srcStream);
int dstRange = getIndexRange(dstStream);
if (srcRange == 0) {
Log.e(TAG, "rescaleIndex : index range should not be zero");
return mStreamStates[dstStream].getMinIndex();
}
return mStreamStates[dstStream].getMinIndex()
+ ((index - mStreamStates[srcStream].getMinIndex()) * dstRange + srcRange / 2)
/ srcRange;
}
Afterwards, the stream type is processed AudioSystem.STREAM_MUSIC, Bluetooth is used, and the absolute volume is set, that is, a message is sent to set the volume value.
AudioSystem.DEVICE_OUT_HEARING_AIDThen , when the device is and the stream type is assistive hearing, a message is sent to Bluetooth to set the volume.
Afterwards, when the stream type is AudioSystem.STREAM_MUSIC, the system audio volume will also be set, mainly to set the HDMI volume as needed.
Afterwards, if the stream type is AudioSystem.STREAM_MUSICand the device is a fixed volume device, correct the incoming volume value.
Afterwards, check whether the corrected volume value is a safe volume, if not, send the stream volume command; if so, onSetStreamVolume()set the stream volume through .
onSetStreamVolume()The implementation is as follows:
private void onSetStreamVolume(int streamType, int index, int flags, int device,
String caller, boolean hasModifyAudioSettings) {
final int stream = mStreamVolumeAlias[streamType];
setStreamVolumeInt(stream, index, device, false, caller, hasModifyAudioSettings);
// setting volume on ui sounds stream type also controls silent mode
if (((flags & AudioManager.FLAG_ALLOW_RINGER_MODES) != 0) ||
(stream == getUiSoundsStreamType())) {
setRingerMode(getNewRingerMode(stream, index, flags),
TAG + ".onSetStreamVolume", false /*external*/);
}
// setting non-zero volume for a muted stream unmutes the stream and vice versa,
// except for BT SCO stream where only explicit mute is allowed to comply to BT requirements
if (streamType != AudioSystem.STREAM_BLUETOOTH_SCO) {
mStreamStates[stream].mute(index == 0);
}
}
. . . . . .
/**
* Sets the stream state's index, and posts a message to set system volume.
* This will not call out to the UI. Assumes a valid stream type.
*
* @param streamType Type of the stream
* @param index Desired volume index of the stream
* @param device the device whose volume must be changed
* @param force If true, set the volume even if the desired volume is same
* @param caller
* @param hasModifyAudioSettings true if the caller is granted MODIFY_AUDIO_SETTINGS or
* MODIFY_AUDIO_ROUTING permission
* as the current volume.
*/
private void setStreamVolumeInt(int streamType,
int index,
int device,
boolean force,
String caller, boolean hasModifyAudioSettings) {
if (isFullVolumeDevice(device)) {
return;
}
VolumeStreamState streamState = mStreamStates[streamType];
if (streamState.setIndex(index, device, caller, hasModifyAudioSettings) || 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);
}
}
Here, the maintained information about the volume of the stream will be updated first. When the volume really changes, a broadcast will be sent; then a message will be sent to set the volume of the device. Here's how to set the device volume:
/*package*/ void setDeviceVolume(VolumeStreamState streamState, int device) {
synchronized (VolumeStreamState.class) {
// Apply volume
streamState.applyDeviceVolume_syncVSS(device);
// Apply change to all streams using this one as alias
int 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 selected
int streamDevice = getDeviceForStream(streamType);
if ((device != streamDevice) && mAvrcpAbsVolSupported
&& AudioSystem.DEVICE_OUT_ALL_A2DP_SET.contains(device)) {
mStreamStates[streamType].applyDeviceVolume_syncVSS(device);
}
mStreamStates[streamType].applyDeviceVolume_syncVSS(streamDevice);
}
}
}
// Post a persist volume msg
sendMsg(mAudioHandler,
MSG_PERSIST_VOLUME,
SENDMSG_QUEUE,
device,
0,
streamState,
PERSIST_DELAY);
}
When setting the volume of a device, first set the volume of the incoming device, then set the volume of the alias device, and then send a message to persist the volume setting. To set the device volume, you must ultimately AudioSystemexecute it through:
private void setStreamVolumeIndex(int index, int device) {
// Only set audio policy BT SCO stream volume to 0 when the stream is actually muted.
// This allows RX path muting by the audio HAL only when explicitly muted but not when
// index is just set to 0 to repect BT requirements
if (mStreamType == AudioSystem.STREAM_BLUETOOTH_SCO && index == 0
&& !isFullyMuted()) {
index = 1;
}
AudioSystem.setStreamVolumeIndexAS(mStreamType, index, device);
}
// must be called while synchronized VolumeStreamState.class
/*package*/ void applyDeviceVolume_syncVSS(int device) {
int index;
if (isFullyMuted()) {
index = 0;
} else if (AudioSystem.DEVICE_OUT_ALL_A2DP_SET.contains(device)
&& mAvrcpAbsVolSupported) {
index = getAbsoluteVolumeIndex((getIndex(device) + 5)/10);
} else if (isFullVolumeDevice(device)) {
index = (mIndexMax + 5)/10;
} else if (device == AudioSystem.DEVICE_OUT_HEARING_AID) {
index = (mIndexMax + 5)/10;
} else {
index = (getIndex(device) + 5)/10;
}
setStreamVolumeIndex(index, device);
}
AudioSystemThe AudioSystem.setStreamVolumeIndexAS(mStreamType, index, device)method is defined as follows:
/** @hide Wrapper for native methods called from AudioService */
public static int setStreamVolumeIndexAS(int stream, int index, int device) {
if (DEBUG_VOLUME) {
Log.i(TAG, "setStreamVolumeIndex: " + STREAM_NAMES[stream]
+ " dev=" + Integer.toHexString(device) + " idx=" + index);
}
return setStreamVolumeIndex(stream, index, device);
}
. . . . . .
@UnsupportedAppUsage
private static native int setStreamVolumeIndex(int stream, int index, int device);
Ultimately, this is done via static JNI native layer methods defined in frameworks/base/core/jni/android_media_AudioSystem.cpp :
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));
}
Back again setStreamVolume(), after that, if the stream type is AudioSystem.STREAM_MUSICand the volume changes, a report is sent to the HDMI service.
Finally, send the volume update report to the volume controller.
AudioSystemWe have seen setAudioPortConfig(config)two AudioSystem.setStreamVolumeIndex(stream, index, device)methods of setting the volume of a device. In both methods, they frameworks/av/media/libaudioclient/AudioSystem.cppcomplete the operation through functions defined by . In this process, you can also see that stream type is a concept maintained by the local layer.
Volume settings in Audio policy service
Following the above process, continue to look at AudioSystem::setStreamVolumeIndex()the implementation of . The local layer is implemented AudioSystemin libaudioclient. AudioSystem::setStreamVolumeIndex()The definition of the function ( frameworks/av/media/libaudioclient/AudioSystem.cpp ) is as follows:
// establish binder interface to AudioPolicy service
const sp<IAudioPolicyService> AudioSystem::get_audio_policy_service() {
sp<IAudioPolicyService> ap;
sp<AudioPolicyServiceClient> apc;
{
Mutex::Autolock _l(gLockAPS);
if (gAudioPolicyService == 0) {
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
do {
binder = sm->getService(String16("media.audio_policy"));
if (binder != 0)
break;
ALOGW("AudioPolicyService not published, waiting...");
usleep(500000); // 0.5 s
} while (true);
if (gAudioPolicyServiceClient == NULL) {
gAudioPolicyServiceClient = new AudioPolicyServiceClient();
}
binder->linkToDeath(gAudioPolicyServiceClient);
gAudioPolicyService = interface_cast<IAudioPolicyService>(binder);
LOG_ALWAYS_FATAL_IF(gAudioPolicyService == 0);
apc = gAudioPolicyServiceClient;
// Make sure callbacks can be received by gAudioPolicyServiceClient
ProcessState::self()->startThreadPool();
}
ap = gAudioPolicyService;
}
if (apc != 0) {
int64_t token = IPCThreadState::self()->clearCallingIdentity();
ap->registerClient(apc);
ap->setAudioPortCallbacksEnabled(apc->isAudioPortCbEnabled());
ap->setAudioVolumeGroupCallbacksEnabled(apc->isAudioVolumeGroupCbEnabled());
IPCThreadState::self()->restoreCallingIdentity(token);
}
return ap;
}
. . . . . .
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;
media::AudioStreamType streamAidl = VALUE_OR_RETURN_STATUS(
legacy2aidl_audio_stream_type_t_AudioStreamType(stream));
int32_t indexAidl = VALUE_OR_RETURN_STATUS(convertIntegral<int32_t>(index));
int32_t deviceAidl = VALUE_OR_RETURN_STATUS(legacy2aidl_audio_devices_t_int32_t(device));
return statusTFromBinderStatus(
aps->setStreamVolumeIndex(streamAidl, deviceAidl, indexAidl));
}
AudioSystemThrough the binder mechanism, access the audio policy service to set the stream volume.
Audio policy service is a system service running in audioserver ( frameworks/av/media/audioserver ). Its implementation consists of multiple components and dynamic link libraries. The overall structure is as follows:
AudioPolicyServiceThe class is the IPC interface layer of the audio policy service and is a proxy for the server. It directly receives requests from the client and also encapsulates other components to assist in completing some specific operations. AudioPolicyServiceThe specific implementation of class member functions is mainly distributed in two files. One is frameworks/av/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp . As its file name indicates, it is mainly the implementation of interface functions; the second is frameworks/av/ services/audiopolicy/service/AudioPolicyService.cpp , contains the implementation of other member functions.
AudioPolicyServiceClass encapsulation AudioPolicyInterface, that is, AudioPolicyManagerto help it complete the main audio strategy logic. AudioPolicyManagerThe specific customized version implementation can be dynamically loaded. The dynamic link library file name of the specific customized version implementation needs to be libaudiopolicymanagercustom.so . The android system provides a default implementation. If the customized version implementation does not exist, this default implementation will be used. The relevant logic is implemented as follows:
static AudioPolicyInterface* createAudioPolicyManager(AudioPolicyClientInterface *clientInterface)
{
AudioPolicyManager *apm = new AudioPolicyManager(clientInterface);
status_t status = apm->initialize();
if (status != NO_ERROR) {
delete apm;
apm = nullptr;
}
return apm;
}
static void destroyAudioPolicyManager(AudioPolicyInterface *interface)
{
delete interface;
}
// ----------------------------------------------------------------------------
AudioPolicyService::AudioPolicyService()
: BnAudioPolicyService(),
mAudioPolicyManager(NULL),
mAudioPolicyClient(NULL),
mPhoneState(AUDIO_MODE_INVALID),
mCaptureStateNotifier(false),
mCreateAudioPolicyManager(createAudioPolicyManager),
mDestroyAudioPolicyManager(destroyAudioPolicyManager) {
}
void AudioPolicyService::loadAudioPolicyManager()
{
mLibraryHandle = dlopen(kAudioPolicyManagerCustomPath, RTLD_NOW);
if (mLibraryHandle != nullptr) {
ALOGI("%s loading %s", __func__, kAudioPolicyManagerCustomPath);
mCreateAudioPolicyManager = reinterpret_cast<CreateAudioPolicyManagerInstance>
(dlsym(mLibraryHandle, "createAudioPolicyManager"));
const char *lastError = dlerror();
ALOGW_IF(mCreateAudioPolicyManager == nullptr, "%s createAudioPolicyManager is null %s",
__func__, lastError != nullptr ? lastError : "no error");
mDestroyAudioPolicyManager = reinterpret_cast<DestroyAudioPolicyManagerInstance>(
dlsym(mLibraryHandle, "destroyAudioPolicyManager"));
lastError = dlerror();
ALOGW_IF(mDestroyAudioPolicyManager == nullptr, "%s destroyAudioPolicyManager is null %s",
__func__, lastError != nullptr ? lastError : "no error");
if (mCreateAudioPolicyManager == nullptr || mDestroyAudioPolicyManager == nullptr){
unloadAudioPolicyManager();
LOG_ALWAYS_FATAL("could not find audiopolicymanager interface methods");
}
}
}
void AudioPolicyService::onFirstRef()
{
{
Mutex::Autolock _l(mLock);
// start audio commands thread
mAudioCommandThread = new AudioCommandThread(String8("ApmAudio"), this);
// start output activity command thread
mOutputCommandThread = new AudioCommandThread(String8("ApmOutput"), this);
mAudioPolicyClient = new AudioPolicyClient(this);
loadAudioPolicyManager();
mAudioPolicyManager = mCreateAudioPolicyManager(mAudioPolicyClient);
}
// load audio processing modules
sp<AudioPolicyEffects> audioPolicyEffects = new AudioPolicyEffects();
sp<UidPolicy> uidPolicy = new UidPolicy(this);
sp<SensorPrivacyPolicy> sensorPrivacyPolicy = new SensorPrivacyPolicy(this);
{
Mutex::Autolock _l(mLock);
mAudioPolicyEffects = audioPolicyEffects;
mUidPolicy = uidPolicy;
mSensorPrivacyPolicy = sensorPrivacyPolicy;
}
uidPolicy->registerSelf();
sensorPrivacyPolicy->registerSelf();
// Create spatializer if supported
if (mAudioPolicyManager != nullptr) {
Mutex::Autolock _l(mLock);
const audio_attributes_t attr = attributes_initializer(AUDIO_USAGE_MEDIA);
AudioDeviceTypeAddrVector devices;
bool hasSpatializer = mAudioPolicyManager->canBeSpatialized(&attr, nullptr, devices);
if (hasSpatializer) {
mSpatializer = Spatializer::create(this);
}
}
AudioSystem::audioPolicyReady();
}
void AudioPolicyService::unloadAudioPolicyManager()
{
ALOGV("%s ", __func__);
if (mLibraryHandle != nullptr) {
dlclose(mLibraryHandle);
}
mLibraryHandle = nullptr;
mCreateAudioPolicyManager = nullptr;
mDestroyAudioPolicyManager = nullptr;
}
AudioPolicyManagerConfiguration information will be loaded from files such as audio_policy_configuration.xml , which maintains EngineInterfaceinformation such as the relationship between stream types and devices, and is also EngineInterfaceobtained by dynamic loading:
status_t AudioPolicyManager::initialize() {
{
std::string path = "libaudiopolicyengine" + getConfig().getEngineLibraryNameSuffix() + ".so";
ALOGD("%s: libaudiopolicyengine file path %s", __FUNCTION__, path.c_str());
auto engLib = EngineLibrary::load(path);
if (!engLib) {
ALOGE("%s: Failed to load the engine library", __FUNCTION__);
return NO_INIT;
}
mEngine = engLib->createEngine();
if (mEngine == nullptr) {
ALOGE("%s: Failed to instantiate the APM engine", __FUNCTION__);
return NO_INIT;
}
}
mEngine->setObserver(this);
status_t status = mEngine->initCheck();
if (status != NO_ERROR) {
LOG_FATAL("Policy engine not initialized(err=%d)", status);
return status;
}
mCommunnicationStrategy = mEngine->getProductStrategyForAttributes(
mEngine->getAttributesForStreamType(AUDIO_STREAM_VOICE_CALL));
// after parsing the config, mOutputDevicesAll and mInputDevicesAll contain all known devices;
// open all output streams needed to access attached devices
onNewAudioModulesAvailableInt(nullptr /*newDevices*/);
// make sure default device is reachable
if (mDefaultOutputDevice == 0 || !mAvailableOutputDevices.contains(mDefaultOutputDevice)) {
ALOGE_IF(mDefaultOutputDevice != 0, "Default device %s is unreachable",
mDefaultOutputDevice->toString().c_str());
status = NO_INIT;
}
// If microphones address is empty, set it according to device type
for (size_t i = 0; i < mAvailableInputDevices.size(); i++) {
if (mAvailableInputDevices[i]->address().empty()) {
if (mAvailableInputDevices[i]->type() == AUDIO_DEVICE_IN_BUILTIN_MIC) {
mAvailableInputDevices[i]->setAddress(AUDIO_BOTTOM_MICROPHONE_ADDRESS);
} else if (mAvailableInputDevices[i]->type() == AUDIO_DEVICE_IN_BACK_MIC) {
mAvailableInputDevices[i]->setAddress(AUDIO_BACK_MICROPHONE_ADDRESS);
}
}
}
ALOGW_IF(mPrimaryOutput == nullptr, "The policy configuration does not declare a primary output");
// Silence ALOGV statements
property_set("log.tag." LOG_TAG, "D");
updateDevicesAndOutputs();
return status;
}
Android provides two EngineInterfaceimplementations, namely libaudiopolicyenginedefault.so located in frameworks/av/services/audiopolicy/enginedefault and libaudiopolicyengineconfigurable.so located in frameworks /av/services/audiopolicy/engineconfigurable . Which one to use is determined by configuration files such as audio_policy_configuration.xml Determined by the configuration items in , libaudiopolicyenginedefault.so is used by default .engine_library
libaudiopolicyenginedefault.so and others load the audio policy engine configuration information from the configuration file /vendor/etc/audio_policy_engine_configuration.xml , which mainly includes product policy, volume group and other information as well as its content type, usage and other information. EngineInterfaceThe device information required for the specific implementation of AudioPolicyManageris obtained from .
Let’s go back to setting the volume. In the audio policy service, this operation request first comes AudioPolicyService::setStreamVolumeIndex():
Status AudioPolicyService::setStreamVolumeIndex(media::AudioStreamType streamAidl,
int32_t deviceAidl, int32_t indexAidl) {
audio_stream_type_t stream = VALUE_OR_RETURN_BINDER_STATUS(
aidl2legacy_AudioStreamType_audio_stream_type_t(streamAidl));
int index = VALUE_OR_RETURN_BINDER_STATUS(convertIntegral<int>(indexAidl));
audio_devices_t device = VALUE_OR_RETURN_BINDER_STATUS(
aidl2legacy_int32_t_audio_devices_t(deviceAidl));
if (mAudioPolicyManager == NULL) {
return binderStatusFromStatusT(NO_INIT);
}
if (!settingsAllowed()) {
return binderStatusFromStatusT(PERMISSION_DENIED);
}
if (uint32_t(stream) >= AUDIO_STREAM_PUBLIC_CNT) {
return binderStatusFromStatusT(BAD_VALUE);
}
Mutex::Autolock _l(mLock);
AutoCallerClear acc;
return binderStatusFromStatusT(mAudioPolicyManager->setStreamVolumeIndex(stream,
index,
device));
}
Here, the incoming parameters are first transformed and then the operation is passed AudioPolicyManager::setStreamVolumeIndex():
status_t AudioPolicyManager::setStreamVolumeIndex(audio_stream_type_t stream,
int index,
audio_devices_t device)
{
auto attributes = mEngine->getAttributesForStreamType(stream);
if (attributes == AUDIO_ATTRIBUTES_INITIALIZER) {
ALOGW("%s: no group for stream %s, bailing out", __func__, toString(stream).c_str());
return NO_ERROR;
}
ALOGD("%s: stream %s attributes=%s", __func__,
toString(stream).c_str(), toString(attributes).c_str());
return setVolumeIndexForAttributes(attributes, index, device);
}
status_t AudioPolicyManager::getStreamVolumeIndex(audio_stream_type_t stream,
int *index,
audio_devices_t device)
{
// if device is AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME, return volume for device selected for this
// stream by the engine.
DeviceTypeSet deviceTypes = {device};
if (device == AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME) {
deviceTypes = mEngine->getOutputDevicesForStream(
stream, true /*fromCache*/).types();
}
return getVolumeIndex(getVolumeCurves(stream), *index, deviceTypes);
}
status_t AudioPolicyManager::setVolumeIndexForAttributes(const audio_attributes_t &attributes,
int index,
audio_devices_t device)
{
// Get Volume group matching the Audio Attributes
auto group = mEngine->getVolumeGroupForAttributes(attributes);
if (group == VOLUME_GROUP_NONE) {
ALOGD("%s: no group matching with %s", __FUNCTION__, toString(attributes).c_str());
return BAD_VALUE;
}
ALOGD("%s: group %d matching with %s", __FUNCTION__, group, toString(attributes).c_str());
status_t status = NO_ERROR;
IVolumeCurves &curves = getVolumeCurves(attributes);
VolumeSource vs = toVolumeSource(group);
product_strategy_t strategy = mEngine->getProductStrategyForAttributes(attributes);
status = setVolumeCurveIndex(index, device, curves);
if (status != NO_ERROR) {
ALOGE("%s failed to set curve index for group %d device 0x%X", __func__, group, device);
return status;
}
DeviceTypeSet curSrcDevices;
auto curCurvAttrs = curves.getAttributes();
if (!curCurvAttrs.empty() && curCurvAttrs.front() != defaultAttr) {
auto attr = curCurvAttrs.front();
curSrcDevices = mEngine->getOutputDevicesForAttributes(attr, nullptr, false).types();
} else if (!curves.getStreamTypes().empty()) {
auto stream = curves.getStreamTypes().front();
curSrcDevices = mEngine->getOutputDevicesForStream(stream, false).types();
} else {
ALOGE("%s: Invalid src %d: no valid attributes nor stream",__func__, vs);
return BAD_VALUE;
}
audio_devices_t curSrcDevice = Volume::getDeviceForVolume(curSrcDevices);
resetDeviceTypes(curSrcDevices, curSrcDevice);
// update volume on all outputs and streams matching the following:
// - The requested stream (or a stream matching for volume control) is active on the output
// - The device (or devices) selected by the engine for this stream includes
// the requested device
// - For non default requested device, currently selected device on the output is either the
// requested device or one of the devices selected by the engine for this stream
// - For default requested device (AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME), apply volume only if
// no specific device volume value exists for currently selected device.
for (size_t i = 0; i < mOutputs.size(); i++) {
sp<SwAudioOutputDescriptor> desc = mOutputs.valueAt(i);
DeviceTypeSet curDevices = desc->devices().types();
if (curDevices.erase(AUDIO_DEVICE_OUT_SPEAKER_SAFE)) {
curDevices.insert(AUDIO_DEVICE_OUT_SPEAKER);
}
if (!(desc->isActive(vs) || isInCall())) {
continue;
}
if (device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME &&
curDevices.find(device) == curDevices.end()) {
continue;
}
bool applyVolume = false;
if (device != AUDIO_DEVICE_OUT_DEFAULT_FOR_VOLUME) {
curSrcDevices.insert(device);
applyVolume = (curSrcDevices.find(
Volume::getDeviceForVolume(curDevices)) != curSrcDevices.end());
} else {
applyVolume = !curves.hasVolumeIndexForDevice(curSrcDevice);
}
if (!applyVolume) {
continue; // next output
}
// Inter / intra volume group priority management: Loop on strategies arranged by priority
// If a higher priority strategy is active, and the output is routed to a device with a
// HW Gain management, do not change the volume
if (desc->useHwGain()) {
applyVolume = false;
for (const auto &productStrategy : mEngine->getOrderedProductStrategies()) {
auto activeClients = desc->clientsList(true /*activeOnly*/, productStrategy,
false /*preferredDevice*/);
if (activeClients.empty()) {
continue;
}
bool isPreempted = false;
bool isHigherPriority = productStrategy < strategy;
for (const auto &client : activeClients) {
if (isHigherPriority && (client->volumeSource() != vs)) {
ALOGV("%s: Strategy=%d (\nrequester:\n"
" group %d, volumeGroup=%d attributes=%s)\n"
" higher priority source active:\n"
" volumeGroup=%d attributes=%s) \n"
" on output %zu, bailing out", __func__, productStrategy,
group, group, toString(attributes).c_str(),
client->volumeSource(), toString(client->attributes()).c_str(), i);
applyVolume = false;
isPreempted = true;
break;
}
// However, continue for loop to ensure no higher prio clients running on output
if (client->volumeSource() == vs) {
applyVolume = true;
}
}
if (isPreempted || applyVolume) {
break;
}
}
if (!applyVolume) {
continue; // next output
}
}
//FIXME: workaround for truncated touch sounds
// delayed volume change for system stream to be removed when the problem is
// handled by system UI
status_t volStatus = checkAndSetVolume(
curves, vs, index, desc, curDevices,
((vs == toVolumeSource(AUDIO_STREAM_SYSTEM))?
TOUCH_SOUND_FIXED_DELAY_MS : 0));
if (volStatus != NO_ERROR) {
status = volStatus;
}
}
mpClientInterface->onAudioVolumeGroupChanged(group, 0 /*flags*/);
return status;
}
status_t AudioPolicyManager::setVolumeCurveIndex(int index,
audio_devices_t device,
IVolumeCurves &volumeCurves)
{
// VOICE_CALL stream has minVolumeIndex > 0 but can be muted directly by an
// app that has MODIFY_PHONE_STATE permission.
bool hasVoice = hasVoiceStream(volumeCurves.getStreamTypes());
if (((index < volumeCurves.getVolumeIndexMin()) && !(hasVoice && index == 0)) ||
(index > volumeCurves.getVolumeIndexMax())) {
ALOGD("%s: wrong index %d min=%d max=%d", __FUNCTION__, index,
volumeCurves.getVolumeIndexMin(), volumeCurves.getVolumeIndexMax());
return BAD_VALUE;
}
if (!audio_is_output_device(device)) {
return BAD_VALUE;
}
// Force max volume if stream cannot be muted
if (!volumeCurves.canBeMuted()) index = volumeCurves.getVolumeIndexMax();
ALOGD("%s device %08x, index %d", __FUNCTION__ , device, index);
volumeCurves.addCurrentVolumeIndex(device, index);
return NO_ERROR;
}
. . . . . .
status_t AudioPolicyManager::checkAndSetVolume(IVolumeCurves &curves,
VolumeSource volumeSource,
int index,
const sp<AudioOutputDescriptor>& outputDesc,
DeviceTypeSet deviceTypes,
int delayMs,
bool force)
{
// do not change actual attributes volume if the attributes is muted
if (outputDesc->isMuted(volumeSource)) {
ALOGVV("%s: volume source %d muted count %d active=%d", __func__, volumeSource,
outputDesc->getMuteCount(volumeSource), outputDesc->isActive(volumeSource));
return NO_ERROR;
}
VolumeSource callVolSrc = toVolumeSource(AUDIO_STREAM_VOICE_CALL);
VolumeSource btScoVolSrc = toVolumeSource(AUDIO_STREAM_BLUETOOTH_SCO);
bool isVoiceVolSrc = callVolSrc == volumeSource;
bool isBtScoVolSrc = btScoVolSrc == volumeSource;
bool isScoRequested = isScoRequestedForComm();
// do not change in call volume if bluetooth is connected and vice versa
// if sco and call follow same curves, bypass forceUseForComm
if ((callVolSrc != btScoVolSrc) &&
((isVoiceVolSrc && isScoRequested) ||
(isBtScoVolSrc && !isScoRequested))) {
ALOGV("%s cannot set volume group %d volume when is%srequested for comm", __func__,
volumeSource, isScoRequested ? " " : "n ot ");
// Do not return an error here as AudioService will always set both voice call
// and bluetooth SCO volumes due to stream aliasing.
return NO_ERROR;
}
if (deviceTypes.empty()) {
deviceTypes = outputDesc->devices().types();
}
float volumeDb = computeVolume(curves, volumeSource, index, deviceTypes);
if (outputDesc->isFixedVolume(deviceTypes) ||
// Force VoIP volume to max for bluetooth SCO device except if muted
(index != 0 && (isVoiceVolSrc || isBtScoVolSrc) &&
isSingleDeviceType(deviceTypes, audio_is_bluetooth_out_sco_device))) {
volumeDb = 0.0f;
}
outputDesc->setVolume(
volumeDb, volumeSource, curves.getStreamTypes(), deviceTypes, delayMs, force);
if (outputDesc == mPrimaryOutput && (isVoiceVolSrc || isBtScoVolSrc)) {
float voiceVolume;
// Force voice volume to max or mute for Bluetooth SCO as other attenuations are managed by the headset
if (isVoiceVolSrc) {
voiceVolume = (float)index/(float)curves.getVolumeIndexMax();
} else {
voiceVolume = index == 0 ? 0.0 : 1.0;
}
if (voiceVolume != mLastVoiceVolume) {
mpClientInterface->setVoiceVolume(voiceVolume, delayMs);
mLastVoiceVolume = voiceVolume;
}
}
return NO_ERROR;
}
AudioPolicyManagerAccording to the index value of the volume, calculate the db value, and then AudioOutputDescriptorset the volume through . AudioOutputDescriptorThere are two implementations in Android, namely SwAudioOutputDescriptorand HwAudioOutputDescriptor, the execution of volume setting comes to SwAudioOutputDescriptor::setVolume():
bool SwAudioOutputDescriptor::setVolume(float volumeDb,
VolumeSource vs, const StreamTypeVector &streamTypes,
const DeviceTypeSet& deviceTypes,
uint32_t delayMs,
bool force)
{
ALOGD("SwAudioOutputDescriptor::%s: volumeDb %f", __FUNCTION__, volumeDb);
StreamTypeVector streams = streamTypes;
if (!AudioOutputDescriptor::setVolume(volumeDb, vs, streamTypes, deviceTypes, delayMs, force)) {
return false;
}
if (streams.empty()) {
streams.push_back(AUDIO_STREAM_MUSIC);
}
for (const auto& devicePort : devices()) {
// APM loops on all group, so filter on active group to set the port gain,
// let the other groups set the stream volume as per legacy
// TODO: Pass in the device address and check against it.
if (isSingleDeviceType(deviceTypes, devicePort->type()) &&
devicePort->hasGainController(true) && isActive(vs)) {
ALOGV("%s: device %s has gain controller", __func__, devicePort->toString().c_str());
// @todo: here we might be in trouble if the SwOutput has several active clients with
// different Volume Source (or if we allow several curves within same volume group)
//
// @todo: default stream volume to max (0) when using HW Port gain?
float volumeAmpl = Volume::DbToAmpl(0);
for (const auto &stream : streams) {
mClientInterface->setStreamVolume(stream, volumeAmpl, mIoHandle, delayMs);
}
AudioGains gains = devicePort->getGains();
int gainMinValueInMb = gains[0]->getMinValueInMb();
int gainMaxValueInMb = gains[0]->getMaxValueInMb();
int gainStepValueInMb = gains[0]->getStepValueInMb();
int gainValueMb = ((volumeDb * 100)/ gainStepValueInMb) * gainStepValueInMb;
gainValueMb = std::max(gainMinValueInMb, std::min(gainValueMb, gainMaxValueInMb));
audio_port_config config = {};
devicePort->toAudioPortConfig(&config);
config.config_mask = AUDIO_PORT_CONFIG_GAIN;
config.gain.values[0] = gainValueMb;
return mClientInterface->setAudioPortConfig(&config, 0) == NO_ERROR;
}
}
// Force VOICE_CALL to track BLUETOOTH_SCO stream volume when bluetooth audio is enabled
float volumeAmpl = Volume::DbToAmpl(getCurVolume(vs));
if (hasStream(streams, AUDIO_STREAM_BLUETOOTH_SCO)) {
mClientInterface->setStreamVolume(AUDIO_STREAM_VOICE_CALL, volumeAmpl, mIoHandle, delayMs);
}
for (const auto &stream : streams) {
ALOGD("%s output %d for volumeSource %d, volume %f, delay %d stream=%s", __func__,
mIoHandle, vs, volumeDb, delayMs, toString(stream).c_str());
mClientInterface->setStreamVolume(stream, volumeAmpl, mIoHandle, delayMs);
}
return true;
}
SwAudioOutputDescriptorAnd AudioPolicyClientInterfaceset the volume through ; AudioPolicyClientInterfacethe implementation is that AudioPolicyService::AudioPolicyClientthe action of setting the volume is AudioPolicyService::AudioPolicyClientreversed by Set the volume via :AudioPolicyServiceAudioPolicyService::setStreamVolume()AudioPolicyService::setStreamVolume()AudioSystem::setStreamVolume()
case SET_VOLUME: {
VolumeData *data = (VolumeData *)command->mParam.get();
ALOGD("AudioCommandThread() processing set volume stream %d, \
volume %f, output %d", data->mStream, data->mVolume, data->mIO);
mLock.unlock();
command->mStatus = AudioSystem::setStreamVolume(data->mStream,
data->mVolume,
data->mIO);
mLock.lock();
}break;
AudioSystem::setStreamVolume()Will request AudioFlingerto set the volume:
status_t AudioSystem::setStreamVolume(audio_stream_type_t stream, float value,
audio_io_handle_t output) {
if (uint32_t(stream) >= AUDIO_STREAM_CNT) return BAD_VALUE;
const sp<IAudioFlinger>& af = AudioSystem::get_audio_flinger();
if (af == 0) return PERMISSION_DENIED;
af->setStreamVolume(stream, value, output);
return NO_ERROR;
}
In this way, the process of adjusting the volume in the audio policy service is as follows:
The Audio policy service receives the volume value in the form of index, converts the index value of the volume into a db value, and then into a gain value, and finally sets the volume gain to the audio flinger.
Volume settings in Audio flinger
Let’s first take a look at the implementation structure of the AudioFlinger service IPC interface layer:
As shown in the figure above, the AudioFlinger service IPC interface layer is implemented as follows AudioFlingerServerAdapter. Its code is actually in the dynamic link library libaudioclient.so . It receives the request, and after receiving the request, passes the request to the real implementer of the service, which is located in frameworks/av/services/audioflinger/ AudioFlinger.cpp AudioFlinger.
Following the above process, AudioFlinger::setStreamVolume()the implementation is as follows:
status_t AudioFlinger::setStreamVolume(audio_stream_type_t stream, float value,
audio_io_handle_t output)
{
ALOGD("AudioFlinger::%s, stream %d, volume %f, output %d", __func__,
static_cast<int>(stream), value, static_cast<int>(output));
// check calling permissions
if (!settingsAllowed()) {
return PERMISSION_DENIED;
}
status_t status = checkStreamType(stream);
if (status != NO_ERROR) {
return status;
}
if (output == AUDIO_IO_HANDLE_NONE) {
return BAD_VALUE;
}
LOG_ALWAYS_FATAL_IF(stream == AUDIO_STREAM_PATCH && value != 1.0f,
"AUDIO_STREAM_PATCH must have full scale volume");
AutoMutex lock(mLock);
VolumeInterface *volumeInterface = getVolumeInterface_l(output);
if (volumeInterface == NULL) {
return BAD_VALUE;
}
volumeInterface->setStreamVolume(stream, value);
return NO_ERROR;
}
. . . . . .
// checkPlaybackThread_l() must be called with AudioFlinger::mLock held
AudioFlinger::VolumeInterface *AudioFlinger::getVolumeInterface_l(audio_io_handle_t output) const
{
VolumeInterface *volumeInterface = mPlaybackThreads.valueFor(output).get();
if (volumeInterface == nullptr) {
MmapThread *mmapThread = mMmapThreads.valueFor(output).get();
if (mmapThread != nullptr) {
if (mmapThread->isOutput()) {
MmapPlaybackThread *mmapPlaybackThread =
static_cast<MmapPlaybackThread *>(mmapThread);
volumeInterface = mmapPlaybackThread;
}
}
}
return volumeInterface;
}
AudioFlingerObtained audio_io_handle_tand AudioFlinger::VolumeInterfacethen set the stream's volume to it. AudioFlingerThe structure of these Threadis as follows:
AudioFlinger::PlaybackThreadThe definition of in frameworks/av/services/audioflinger/Threads.cppsetStreamVolume() is as follows:
void AudioFlinger::PlaybackThread::setStreamVolume(audio_stream_type_t stream, float value)
{
Mutex::Autolock _l(mLock);
mStreamTypes[stream].volume = value;
broadcast_l();
}
AudioFlinger::MmapPlaybackThreadThe definition of setStreamVolume()is as follows:
void AudioFlinger::MmapPlaybackThread::setStreamVolume(audio_stream_type_t stream, float value)
{
Mutex::Autolock _l(mLock);
if (stream == mStreamType) {
mStreamVolume = value;
broadcast_l();
}
}
That is, the volume gain value of the stream is saved and used to gain the audio data when processing the data later.
The process of adjusting the volume from the core Android system to the Audio flinger layer is roughly the same.
Reference documentation:
Done.