Audio focus is a concept introduced in API 8. It is used to convey the fact that a user can * only focus on a single audio stream at a time, e.g. listening to music or a podcast, but not * both at the same time. In some cases, multiple audio streams can be playing at the same time, * but there is only one the user would really listen to (focus on), while the other plays in * the background. An example of this is driving directions being spoken while music plays at * a reduced volume (a.k.a. ducking). *
When an application requests audio focus, it expresses its intention to “own” audio focus to * play audio. Let’s review the different types of focus requests, the return value after a request, * and the responses to a loss. *
Note: applications should not play anything until granted focus.
* *There are four focus request types. A successful focus request with each will yield different * behaviors by the system and the other application that previously held audio focus. *
An {@code AudioFocusRequest} instance always contains one of the four types of requests * explained above. It is passed when building an {@code AudioFocusRequest} instance with its * builder in the {@link Builder} constructor * {@link AudioFocusRequest.Builder#AudioFocusRequest.Builder(int)}, or * with {@link AudioFocusRequest.Builder#setFocusGain(int)} after copying an existing instance with * {@link AudioFocusRequest.Builder#AudioFocusRequest.Builder(AudioFocusRequest)}. * *
Any focus request is qualified by the {@link AudioAttributes}
* (see {@link Builder#setAudioAttributes(AudioAttributes)}) that describe the audio use case that
* will follow the request (once it's successful or granted). It is recommended to use the
* same {@code AudioAttributes} for the request as the attributes you are using for audio/media
* playback.
*
If no attributes are set, default attributes of {@link AudioAttributes#USAGE_MEDIA} are used.
*
*
Audio focus can be "locked" by the system for a number of reasons: during a phone call, when
* the car to which the device is connected plays an emergency message... To support these
* situations, the application can request to be notified when its request is fulfilled, by flagging
* its request as accepting delayed focus, with {@link Builder#setAcceptsDelayedFocusGain(boolean)}.
*
If focus is requested while being locked by the system,
* {@link AudioManager#requestAudioFocus(AudioFocusRequest)} will return
* {@link AudioManager#AUDIOFOCUS_REQUEST_DELAYED}. When focus isn't locked anymore, the focus
* listener set with {@link Builder#setOnAudioFocusChangeListener(OnAudioFocusChangeListener)}
* or with {@link Builder#setOnAudioFocusChangeListener(OnAudioFocusChangeListener, Handler)} will
* be called to notify the application it now owns audio focus.
*
*
When an application requested audio focus with * {@link AudioManager#AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK}, the system will duck the current focus * owner. *
Note: this behavior is new for Android O, whereas applications targeting * SDK level up to API 25 had to implement the ducking themselves when they received a focus * loss of {@link AudioManager#AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK}. *
But ducking is not always the behavior expected by the user. A typical example is when the * device plays driving directions while the user is listening to an audio book or podcast, and * expects the audio playback to pause, instead of duck, as it is hard to understand a navigation * prompt and spoken content at the same time. Therefore the system will not automatically duck * when it detects it would be ducking spoken content: such content is detected when the * {@code AudioAttributes} of the player are qualified by * {@link AudioAttributes#CONTENT_TYPE_SPEECH}. Refer for instance to * {@link AudioAttributes.Builder#setContentType(int)} and * {@link MediaPlayer#setAudioAttributes(AudioAttributes)} if you are writing a media playback * application for audio book, podcasts... Since the system will not automatically duck applications * that play speech, it calls their focus listener instead to notify them of * {@link AudioManager#AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK}, so they can pause instead. Note that * this behavior is independent of the use of {@code AudioFocusRequest}, but tied to the use * of {@code AudioAttributes}. *
If your application requires pausing instead of ducking for any other reason than playing * speech, you can also declare so with {@link Builder#setWillPauseWhenDucked(boolean)}, which will * cause the system to call your focus listener instead of automatically ducking. * *
The example below covers the following steps to be found in any application that would play * audio, and use audio focus. Here we play an audio book, and our application is intended to pause * rather than duck when it loses focus. These steps consist in: *
*
* // initialization of the audio attributes and focus request
* mAudioManager = (AudioManager) Context.getSystemService(Context.AUDIO_SERVICE);
* mPlaybackAttributes = new AudioAttributes.Builder()
* .setUsage(AudioAttributes.USAGE_MEDIA)
* .setContentType(AudioAttributes.CONTENT_TYPE_SPEECH)
* .build();
* mFocusRequest = new AudioFocusRequest.Builder(AudioManager.AUDIOFOCUS_GAIN)
* .setAudioAttributes(mPlaybackAttributes)
* .setAcceptsDelayedFocusGain(true)
* .setWillPauseWhenDucked(true)
* .setOnAudioFocusChangeListener(this, mMyHandler)
* .build();
* mMediaPlayer = new MediaPlayer();
* mMediaPlayer.setAudioAttributes(mPlaybackAttributes);
* final Object mFocusLock = new Object();
*
* boolean mPlaybackDelayed = false;
*
* // requesting audio focus
* int res = mAudioManager.requestAudioFocus(mFocusRequest);
* synchronized (mFocusLock) {
* if (res == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
* mPlaybackDelayed = false;
* } else if (res == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
* mPlaybackDelayed = false;
* playbackNow();
* } else if (res == AudioManager.AUDIOFOCUS_REQUEST_DELAYED) {
* mPlaybackDelayed = true;
* }
* }
*
* // implementation of the OnAudioFocusChangeListener
* @Override
* public void onAudioFocusChange(int focusChange) {
* switch (focusChange) {
* case AudioManager.AUDIOFOCUS_GAIN:
* if (mPlaybackDelayed || mResumeOnFocusGain) {
* synchronized (mFocusLock) {
* mPlaybackDelayed = false;
* mResumeOnFocusGain = false;
* }
* playbackNow();
* }
* break;
* case AudioManager.AUDIOFOCUS_LOSS:
* synchronized (mFocusLock) {
* // this is not a transient loss, we shouldn't automatically resume for now
* mResumeOnFocusGain = false;
* mPlaybackDelayed = false;
* }
* pausePlayback();
* break;
* case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
* case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
* // we handle all transient losses the same way because we never duck audio books
* synchronized (mFocusLock) {
* // we should only resume if playback was interrupted
* mResumeOnFocusGain = mMediaPlayer.isPlaying();
* mPlaybackDelayed = false;
* }
* pausePlayback();
* break;
* }
* }
*
* // Important:
* // Also set "mResumeOnFocusGain" to false when the user pauses or stops playback: this way your
* // application doesn't automatically restart when it gains focus, even though the user had
* // stopped it.
*
*/
public final class AudioFocusRequest {
// default attributes for the request when not specified
private final static AudioAttributes FOCUS_DEFAULT_ATTR = new AudioAttributes.Builder()
.setUsage(AudioAttributes.USAGE_MEDIA).build();
/** @hide */
public static final String KEY_ACCESSIBILITY_FORCE_FOCUS_DUCKING = "a11y_force_ducking";
private final OnAudioFocusChangeListener mFocusListener; // may be null
private final Handler mListenerHandler; // may be null
private final AudioAttributes mAttr; // never null
private final int mFocusGain;
private final int mFlags;
private AudioFocusRequest(OnAudioFocusChangeListener listener, Handler handler,
AudioAttributes attr, int focusGain, int flags) {
mFocusListener = listener;
mListenerHandler = handler;
mFocusGain = focusGain;
mAttr = attr;
mFlags = flags;
}
/**
* @hide
* Checks whether a focus gain constant is a valid value for an audio focus request.
* @param focusGain value to check
* @return true if focusGain is a valid value for an audio focus request.
*/
final static boolean isValidFocusGain(int focusGain) {
switch (focusGain) {
case AudioManager.AUDIOFOCUS_GAIN:
case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT:
case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK:
case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE:
return true;
default:
return false;
}
}
/**
* @hide
* Returns the focus change listener set for this {@code AudioFocusRequest}.
* @return null if no {@link AudioManager.OnAudioFocusChangeListener} was set.
*/
public @Nullable OnAudioFocusChangeListener getOnAudioFocusChangeListener() {
return mFocusListener;
}
/**
* @hide
* Returns the {@link Handler} to be used for the focus change listener.
* @return the same {@code Handler} set in.
* {@link Builder#setOnAudioFocusChangeListener(OnAudioFocusChangeListener, Handler)}, or null
* if no listener was set.
*/
public @Nullable Handler getOnAudioFocusChangeListenerHandler() {
return mListenerHandler;
}
/**
* Returns the {@link AudioAttributes} set for this {@code AudioFocusRequest}, or the default
* attributes if none were set.
* @return non-null {@link AudioAttributes}.
*/
public @NonNull AudioAttributes getAudioAttributes() {
return mAttr;
}
/**
* Returns the type of audio focus request configured for this {@code AudioFocusRequest}.
* @return one of {@link AudioManager#AUDIOFOCUS_GAIN},
* {@link AudioManager#AUDIOFOCUS_GAIN_TRANSIENT},
* {@link AudioManager#AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK}, and
* {@link AudioManager#AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE}.
*/
public int getFocusGain() {
return mFocusGain;
}
/**
* Returns whether the application that would use this {@code AudioFocusRequest} would pause
* when it is requested to duck.
* @return the duck/pause behavior.
*/
public boolean willPauseWhenDucked() {
return (mFlags & AudioManager.AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS)
== AudioManager.AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS;
}
/**
* Returns whether the application that would use this {@code AudioFocusRequest} supports
* a focus gain granted after a temporary request failure.
* @return whether delayed focus gain is supported.
*/
public boolean acceptsDelayedFocusGain() {
return (mFlags & AudioManager.AUDIOFOCUS_FLAG_DELAY_OK)
== AudioManager.AUDIOFOCUS_FLAG_DELAY_OK;
}
/**
* @hide
* Returns whether audio focus will be locked (i.e. focus cannot change) as a result of this
* focus request being successful.
* @return whether this request will lock focus.
*/
@SystemApi
public boolean locksFocus() {
return (mFlags & AudioManager.AUDIOFOCUS_FLAG_LOCK)
== AudioManager.AUDIOFOCUS_FLAG_LOCK;
}
int getFlags() {
return mFlags;
}
/**
* Builder class for {@link AudioFocusRequest} objects.
* See {@link AudioFocusRequest} for an example of building an instance with this builder.
*
The default values for the instance to be built are:
*
| focus listener and handler | none |
| {@code AudioAttributes} | attributes with usage set to * {@link AudioAttributes#USAGE_MEDIA} |
| pauses on duck | false |
| supports delayed focus grant | false |
By default there is no focus change listener, delayed focus is not supported, ducking
* is suitable for the application, and the AudioAttributes
* have a usage of {@link AudioAttributes#USAGE_MEDIA}.
* @param focusGain the type of audio focus gain that will be requested
* @throws IllegalArgumentException thrown when an invalid focus gain type is used
*/
public Builder(int focusGain) {
setFocusGain(focusGain);
}
/**
* Constructs a new {@code Builder} with all the properties of the {@code AudioFocusRequest}
* passed as parameter.
* Use this method when you want a new request to differ only by some properties.
* @param requestToCopy the non-null {@code AudioFocusRequest} to build a duplicate from.
* @throws IllegalArgumentException thrown when a null {@code AudioFocusRequest} is used.
*/
public Builder(@NonNull AudioFocusRequest requestToCopy) {
if (requestToCopy == null) {
throw new IllegalArgumentException("Illegal null AudioFocusRequest");
}
mAttr = requestToCopy.mAttr;
mFocusListener = requestToCopy.mFocusListener;
mListenerHandler = requestToCopy.mListenerHandler;
mFocusGain = requestToCopy.mFocusGain;
mPausesOnDuck = requestToCopy.willPauseWhenDucked();
mDelayedFocus = requestToCopy.acceptsDelayedFocusGain();
}
/**
* Sets the type of focus gain that will be requested.
* Use this method to replace the focus gain when building a request by modifying an
* existing {@code AudioFocusRequest} instance.
* @param focusGain the type of audio focus gain that will be requested.
* @return this {@code Builder} instance
* @throws IllegalArgumentException thrown when an invalid focus gain type is used
*/
public @NonNull Builder setFocusGain(int focusGain) {
if (!isValidFocusGain(focusGain)) {
throw new IllegalArgumentException("Illegal audio focus gain type " + focusGain);
}
mFocusGain = focusGain;
return this;
}
/**
* Sets the listener called when audio focus changes after being requested with
* {@link AudioManager#requestAudioFocus(AudioFocusRequest)}, and until being abandoned
* with {@link AudioManager#abandonAudioFocusRequest(AudioFocusRequest)}.
* Note that only focus changes (gains and losses) affecting the focus owner are reported,
* not gains and losses of other focus requesters in the system.
* Notifications are delivered on the main {@link Looper}.
* @param listener the listener receiving the focus change notifications.
* @return this {@code Builder} instance.
* @throws NullPointerException thrown when a null focus listener is used.
*/
public @NonNull Builder setOnAudioFocusChangeListener(
@NonNull OnAudioFocusChangeListener listener) {
if (listener == null) {
throw new NullPointerException("Illegal null focus listener");
}
mFocusListener = listener;
mListenerHandler = null;
return this;
}
/**
* @hide
* Internal listener setter, no null checks on listener nor handler
* @param listener
* @param handler
* @return this {@code Builder} instance.
*/
@NonNull Builder setOnAudioFocusChangeListenerInt(
OnAudioFocusChangeListener listener, Handler handler) {
mFocusListener = listener;
mListenerHandler = handler;
return this;
}
/**
* Sets the listener called when audio focus changes after being requested with
* {@link AudioManager#requestAudioFocus(AudioFocusRequest)}, and until being abandoned
* with {@link AudioManager#abandonAudioFocusRequest(AudioFocusRequest)}.
* Note that only focus changes (gains and losses) affecting the focus owner are reported,
* not gains and losses of other focus requesters in the system.
* @param listener the listener receiving the focus change notifications.
* @param handler the {@link Handler} for the thread on which to execute
* the notifications.
* @return this {@code Builder} instance.
* @throws NullPointerException thrown when a null focus listener or handler is used.
*/
public @NonNull Builder setOnAudioFocusChangeListener(
@NonNull OnAudioFocusChangeListener listener, @NonNull Handler handler) {
if (listener == null || handler == null) {
throw new NullPointerException("Illegal null focus listener or handler");
}
mFocusListener = listener;
mListenerHandler = handler;
return this;
}
/**
* Sets the {@link AudioAttributes} to be associated with the focus request, and which
* describe the use case for which focus is requested.
* As the focus requests typically precede audio playback, this information is used on
* certain platforms to declare the subsequent playback use case. It is therefore good
* practice to use in this method the same {@code AudioAttributes} as used for
* playback, see for example {@link MediaPlayer#setAudioAttributes(AudioAttributes)} in
* {@code MediaPlayer} or {@link AudioTrack.Builder#setAudioAttributes(AudioAttributes)}
* in {@code AudioTrack}.
* @param attributes the {@link AudioAttributes} for the focus request.
* @return this {@code Builder} instance.
* @throws NullPointerException thrown when using null for the attributes.
*/
public @NonNull Builder setAudioAttributes(@NonNull AudioAttributes attributes) {
if (attributes == null) {
throw new NullPointerException("Illegal null AudioAttributes");
}
mAttr = attributes;
return this;
}
/**
* Declare the intended behavior of the application with regards to audio ducking.
* See more details in the {@link AudioFocusRequest} class documentation.
* @param pauseOnDuck use {@code true} if the application intends to pause audio playback
* when losing focus with {@link AudioManager#AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK}.
* If {@code true}, note that you must also set a focus listener to receive such an
* event, with
* {@link #setOnAudioFocusChangeListener(OnAudioFocusChangeListener, Handler)}.
* @return this {@code Builder} instance.
*/
public @NonNull Builder setWillPauseWhenDucked(boolean pauseOnDuck) {
mPausesOnDuck = pauseOnDuck;
return this;
}
/**
* Marks this focus request as compatible with delayed focus.
* See more details about delayed focus in the {@link AudioFocusRequest} class
* documentation.
* @param acceptsDelayedFocusGain use {@code true} if the application supports delayed
* focus. If {@code true}, note that you must also set a focus listener to be notified
* of delayed focus gain, with
* {@link #setOnAudioFocusChangeListener(OnAudioFocusChangeListener, Handler)}.
* @return this {@code Builder} instance
*/
public @NonNull Builder setAcceptsDelayedFocusGain(boolean acceptsDelayedFocusGain) {
mDelayedFocus = acceptsDelayedFocusGain;
return this;
}
/**
* @hide
* Marks this focus request as locking audio focus so granting is temporarily disabled.
* This feature can only be used by owners of a registered
* {@link android.media.audiopolicy.AudioPolicy} in
* {@link AudioManager#requestAudioFocus(AudioFocusRequest, android.media.audiopolicy.AudioPolicy)}.
* Setting to false is the same as the default behavior.
* @param focusLocked true when locking focus
* @return this {@code Builder} instance
*/
@SystemApi
public @NonNull Builder setLocksFocus(boolean focusLocked) {
mFocusLocked = focusLocked;
return this;
}
/**
* Marks this focus request as forcing ducking, regardless of the conditions in which
* the system would or would not enforce ducking.
* Forcing ducking will only be honored when requesting AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK
* with an {@link AudioAttributes} usage of
* {@link AudioAttributes#USAGE_ASSISTANCE_ACCESSIBILITY}, coming from an accessibility
* service, and will be ignored otherwise.
* @param forceDucking {@code true} to force ducking
* @return this {@code Builder} instance
*/
public @NonNull Builder setForceDucking(boolean forceDucking) {
mA11yForceDucking = forceDucking;
return this;
}
/**
* Builds a new {@code AudioFocusRequest} instance combining all the information gathered
* by this {@code Builder}'s configuration methods.
* @return the {@code AudioFocusRequest} instance qualified by all the properties set
* on this {@code Builder}.
* @throws IllegalStateException thrown when attempting to build a focus request that is set
* to accept delayed focus, or to pause on duck, but no focus change listener was set.
*/
public AudioFocusRequest build() {
if ((mDelayedFocus || mPausesOnDuck) && (mFocusListener == null)) {
throw new IllegalStateException(
"Can't use delayed focus or pause on duck without a listener");
}
if (mA11yForceDucking) {
final Bundle extraInfo;
if (mAttr.getBundle() == null) {
extraInfo = new Bundle();
} else {
extraInfo = mAttr.getBundle();
}
// checking of usage and focus request is done server side
extraInfo.putBoolean(KEY_ACCESSIBILITY_FORCE_FOCUS_DUCKING, true);
mAttr = new AudioAttributes.Builder(mAttr).addBundle(extraInfo).build();
}
final int flags = 0
| (mDelayedFocus ? AudioManager.AUDIOFOCUS_FLAG_DELAY_OK : 0)
| (mPausesOnDuck ? AudioManager.AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS : 0)
| (mFocusLocked ? AudioManager.AUDIOFOCUS_FLAG_LOCK : 0);
return new AudioFocusRequest(mFocusListener, mListenerHandler,
mAttr, mFocusGain, flags);
}
}
}