public class SoundPool extends Object
A SoundPool is a collection of samples that can be loaded into memory from a resource inside the APK or from a file in the file system. The SoundPool library uses the MediaPlayer service to decode the audio into a raw 16-bit PCM mono or stereo stream. This allows applications to ship with compressed streams without having to suffer the CPU load and latency of decompressing during playback.
In addition to low-latency playback, SoundPool can also manage the number of audio streams being rendered at once. When the SoundPool object is constructed, the maxStreams parameter sets the maximum number of streams that can be played at a time from this single SoundPool. SoundPool tracks the number of active streams. If the maximum number of streams is exceeded, SoundPool will automatically stop a previously playing stream based first on priority and then by age within that priority. Limiting the maximum number of streams helps to cap CPU loading and reducing the likelihood that audio mixing will impact visuals or UI performance.
Sounds can be looped by setting a non-zero loop value. A value of -1 causes the sound to loop forever. In this case, the application must explicitly call the stop() function to stop the sound. Any other non-zero value will cause the sound to repeat the specified number of times, e.g. a value of 3 causes the sound to play a total of 4 times.
The playback rate can also be changed. A playback rate of 1.0 causes the sound to play at its original frequency (resampled, if necessary, to the hardware output frequency). A playback rate of 2.0 causes the sound to play at twice its original frequency, and a playback rate of 0.5 causes it to play at half its original frequency. The playback rate range is 0.5 to 2.0.
Priority runs low to high, i.e. higher numbers are higher priority. Priority is used when a call to play() would cause the number of active streams to exceed the value established by the maxStreams parameter when the SoundPool was created. In this case, the stream allocator will stop the lowest priority stream. If there are multiple streams with the same low priority, it will choose the oldest stream to stop. In the case where the priority of the new stream is lower than all the active streams, the new sound will not play and the play() function will return a streamID of zero.
Let's examine a typical use case: A game consists of several levels of play. For each level, there is a set of unique sounds that are used only by that level. In this case, the game logic should create a new SoundPool object when the first level is loaded. The level data itself might contain the list of sounds to be used by this level. The loading logic iterates through the list of sounds calling the appropriate SoundPool.load() function. This should typically be done early in the process to allow time for decompressing the audio to raw PCM format before they are needed for playback.
Once the sounds are loaded and play has started, the application can trigger sounds by calling SoundPool.play(). Playing streams can be paused or resumed, and the application can also alter the pitch by adjusting the playback rate in real-time for doppler or synthesis effects.
Note that since streams can be stopped due to resource constraints, the streamID is a reference to a particular instance of a stream. If the stream is stopped to allow a higher priority stream to play, the stream is no longer be valid. However, the application is allowed to call methods on the streamID without error. This may help simplify program logic since the application need not concern itself with the stream lifecycle.
In our example, when the player has completed the level, the game logic should call SoundPool.release() to release all the native resources in use and then set the SoundPool reference to null. If the player starts another level, a new SoundPool is created, sounds are loaded, and play resumes.
| Modifier and Type | Class and Description |
|---|---|
static interface |
SoundPool.OnLoadCompleteListener
Interface definition for a callback to be invoked when all the
sounds are loaded.
|
| Constructor and Description |
|---|
SoundPool(int maxStreams,
int streamType,
int srcQuality)
Constructor.
|
| Modifier and Type | Method and Description |
|---|---|
void |
autoPause()
Pause all active streams.
|
void |
autoResume()
Resume all previously active streams.
|
protected void |
finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
|
int |
load(AssetFileDescriptor afd,
int priority)
Load the sound from an asset file descriptor.
|
int |
load(Context context,
int resId,
int priority)
Load the sound from the specified APK resource.
|
int |
load(FileDescriptor fd,
long offset,
long length,
int priority)
Load the sound from a FileDescriptor.
|
int |
load(String path,
int priority)
Load the sound from the specified path.
|
void |
pause(int streamID)
Pause a playback stream.
|
int |
play(int soundID,
float leftVolume,
float rightVolume,
int priority,
int loop,
float rate)
Play a sound from a sound ID.
|
void |
release()
Release the SoundPool resources.
|
void |
resume(int streamID)
Resume a playback stream.
|
void |
setLoop(int streamID,
int loop)
Set loop mode.
|
void |
setOnLoadCompleteListener(SoundPool.OnLoadCompleteListener listener)
Sets the callback hook for the OnLoadCompleteListener.
|
void |
setPriority(int streamID,
int priority)
Change stream priority.
|
void |
setRate(int streamID,
float rate)
Change playback rate.
|
void |
setVolume(int streamID,
float leftVolume,
float rightVolume)
Set stream volume.
|
void |
stop(int streamID)
Stop a playback stream.
|
boolean |
unload(int soundID)
Unload a sound from a sound ID.
|
public SoundPool(int maxStreams,
int streamType,
int srcQuality)
maxStreams - the maximum number of simultaneous streams for this
SoundPool objectstreamType - the audio stream type as described in AudioManager
For example, game applications will normally use
AudioManager.STREAM_MUSIC.srcQuality - the sample-rate converter quality. Currently has no
effect. Use 0 for the default.public int load(String path, int priority)
path - the path to the audio filepriority - the priority of the sound. Currently has no effect. Use
a value of 1 for future compatibility.public int load(Context context, int resId, int priority)
context - the application contextresId - the resource IDpriority - the priority of the sound. Currently has no effect. Use
a value of 1 for future compatibility.public int load(AssetFileDescriptor afd, int priority)
afd - an asset file descriptorpriority - the priority of the sound. Currently has no effect. Use
a value of 1 for future compatibility.public int load(FileDescriptor fd, long offset, long length, int priority)
fd - a FileDescriptor objectoffset - offset to the start of the soundlength - length of the soundpriority - the priority of the sound. Currently has no effect. Use
a value of 1 for future compatibility.public final boolean unload(int soundID)
soundID - a soundID returned by the load() functionpublic final int play(int soundID,
float leftVolume,
float rightVolume,
int priority,
int loop,
float rate)
soundID - a soundID returned by the load() functionleftVolume - left volume value (range = 0.0 to 1.0)rightVolume - right volume value (range = 0.0 to 1.0)priority - stream priority (0 = lowest priority)loop - loop mode (0 = no loop, -1 = loop forever)rate - playback rate (1.0 = normal playback, range 0.5 to 2.0)public final void pause(int streamID)
streamID - a streamID returned by the play() functionpublic final void resume(int streamID)
streamID - a streamID returned by the play() functionpublic final void autoPause()
public final void autoResume()
public final void stop(int streamID)
streamID - a streamID returned by the play() functionpublic final void setVolume(int streamID,
float leftVolume,
float rightVolume)
streamID - a streamID returned by the play() functionleftVolume - left volume value (range = 0.0 to 1.0)rightVolume - right volume value (range = 0.0 to 1.0)public final void setPriority(int streamID,
int priority)
streamID - a streamID returned by the play() functionpublic final void setLoop(int streamID,
int loop)
streamID - a streamID returned by the play() functionloop - loop mode (0 = no loop, -1 = loop forever)public final void setRate(int streamID,
float rate)
streamID - a streamID returned by the play() functionrate - playback rate (1.0 = normal playback, range 0.5 to 2.0)public void setOnLoadCompleteListener(SoundPool.OnLoadCompleteListener listener)
public final void release()
protected void finalize()
ObjectNote that objects that override finalize are significantly more expensive than
objects that don't. Finalizers may be run a long time after the object is no longer
reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup.
Note also that finalizers are run on a single VM-wide finalizer thread,
so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary
for a class that has a native peer and needs to call a native method to destroy that peer.
Even then, it's better to provide an explicit close method (and implement
Closeable), and insist that callers manually dispose of instances. This
works well for something like files, but less well for something like a BigInteger
where typical calling code would have to deal with lots of temporaries. Unfortunately,
code that creates lots of temporaries is the worst kind of code from the point of view of
the single finalizer thread.
If you must use finalizers, consider at least providing your own
ReferenceQueue and having your own thread process that queue.
Unlike constructors, finalizers are not automatically chained. You are responsible for
calling super.finalize() yourself.
Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.