public class

SoundPool

extends Object
java.lang.Object
   ↳ android.media.SoundPool

Class Overview

The SoundPool class manages and plays audio resources for applications.

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.

Summary

Public Constructors
SoundPool(int maxStreams, int streamType, int srcQuality)
Constructor.
Public Methods
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(AssetFileDescriptor afd, int priority)
Load the sound from an asset file descriptor.
int load(String path, int priority)
Load the sound from the specified path.
final void pause(int streamID)
Pause a playback stream.
final int play(int soundID, float leftVolume, float rightVolume, int priority, int loop, float rate)
Play a sound from a sound ID.
final void release()
Release the SoundPool resources.
final void resume(int streamID)
Resume a playback stream.
final void setLoop(int streamID, int loop)
Set loop mode.
final void setPriority(int streamID, int priority)
Change stream priority.
final void setRate(int streamID, float rate)
Change playback rate.
final void setVolume(int streamID, float leftVolume, float rightVolume)
Set stream volume.
final void stop(int streamID)
Stop a playback stream.
final boolean unload(int soundID)
Unload a sound from a sound ID.
Protected Methods
void finalize()
Is called before the object's memory is being reclaimed by the VM.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public SoundPool (int maxStreams, int streamType, int srcQuality)

Since: API Level 1

Constructor. Constructs a SoundPool object with the following characteristics:

Parameters
maxStreams the maximum number of simultaneous streams for this SoundPool object
streamType the audio stream type as described in AudioManager For example, game applications will normally use STREAM_MUSIC.
srcQuality the sample-rate converter quality. Currently has no effect. Use 0 for the default.
Returns
  • a SoundPool object, or null if creation failed

Public Methods

public int load (Context context, int resId, int priority)

Since: API Level 1

Load the sound from the specified APK resource. Note that the extension is dropped. For example, if you want to load a sound from the raw resource file "explosion.mp3", you would specify "R.raw.explosion" as the resource ID. Note that this means you cannot have both an "explosion.wav" and an "explosion.mp3" in the res/raw directory.

Parameters
context the application context
resId the resource ID
priority the priority of the sound. Currently has no effect. Use a value of 1 for future compatibility.
Returns
  • a sound ID. This value can be used to play or unload the sound.

public int load (FileDescriptor fd, long offset, long length, int priority)

Since: API Level 3

Load the sound from a FileDescriptor. This version is useful if you store multiple sounds in a single binary. The offset specifies the offset from the start of the file and the length specifies the length of the sound within the file.

Parameters
fd a FileDescriptor object
offset offset to the start of the sound
length length of the sound
priority the priority of the sound. Currently has no effect. Use a value of 1 for future compatibility.
Returns
  • a sound ID. This value can be used to play or unload the sound.

public int load (AssetFileDescriptor afd, int priority)

Since: API Level 3

Load the sound from an asset file descriptor.

Parameters
afd an asset file descriptor
priority the priority of the sound. Currently has no effect. Use a value of 1 for future compatibility.
Returns
  • a sound ID. This value can be used to play or unload the sound.

public int load (String path, int priority)

Since: API Level 1

Load the sound from the specified path.

Parameters
path the path to the audio file
priority the priority of the sound. Currently has no effect. Use a value of 1 for future compatibility.
Returns
  • a sound ID. This value can be used to play or unload the sound.

public final void pause (int streamID)

Since: API Level 1

Pause a playback stream. Pause the stream specified by the streamID. This is the value returned by the play() function. If the stream is playing, it will be paused. If the stream is not playing (e.g. is stopped or was previously paused), calling this function will have no effect.

Parameters
streamID a streamID returned by the play() function

public final int play (int soundID, float leftVolume, float rightVolume, int priority, int loop, float rate)

Since: API Level 1

Play a sound from a sound ID. Play the sound specified by the soundID. This is the value returned by the load() function. Returns a non-zero streamID if successful, zero if it fails. The streamID can be used to further control playback. Note that calling play() may cause another sound to stop playing if the maximum number of active streams is exceeded. A loop value of -1 means loop forever, a value of 0 means don't loop, other values indicate the number of repeats, e.g. a value of 1 plays the audio twice. The playback rate allows the application to vary the playback rate (pitch) of the sound. A value of 1.0 means play back at the original frequency. A value of 2.0 means play back twice as fast, and a value of 0.5 means playback at half speed.

Parameters
soundID a soundID returned by the load() function
leftVolume 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)
Returns
  • non-zero streamID if successful, zero if failed

public final void release ()

Since: API Level 1

Release the SoundPool resources. Release all memory and native resources used by the SoundPool object. The SoundPool can no longer be used and the reference should be set to null.

public final void resume (int streamID)

Since: API Level 1

Resume a playback stream. Resume the stream specified by the streamID. This is the value returned by the play() function. If the stream is paused, this will resume playback. If the stream was not previously paused, calling this function will have no effect.

Parameters
streamID a streamID returned by the play() function

public final void setLoop (int streamID, int loop)

Since: API Level 1

Set loop mode. Change the loop mode. A loop value of -1 means loop forever, a value of 0 means don't loop, other values indicate the number of repeats, e.g. a value of 1 plays the audio twice. If the stream does not exist, it will have no effect.

Parameters
streamID a streamID returned by the play() function
loop loop mode (0 = no loop, -1 = loop forever)

public final void setPriority (int streamID, int priority)

Since: API Level 1

Change stream priority. Change the priority of the stream specified by the streamID. This is the value returned by the play() function. Affects the order in which streams are re-used to play new sounds. If the stream does not exist, it will have no effect.

Parameters
streamID a streamID returned by the play() function

public final void setRate (int streamID, float rate)

Since: API Level 1

Change playback rate. The playback rate allows the application to vary the playback rate (pitch) of the sound. A value of 1.0 means playback at the original frequency. A value of 2.0 means playback twice as fast, and a value of 0.5 means playback at half speed. If the stream does not exist, it will have no effect.

Parameters
streamID a streamID returned by the play() function
rate playback rate (1.0 = normal playback, range 0.5 to 2.0)

public final void setVolume (int streamID, float leftVolume, float rightVolume)

Since: API Level 1

Set stream volume. Sets the volume on the stream specified by the streamID. This is the value returned by the play() function. The value must be in the range of 0.0 to 1.0. If the stream does not exist, it will have no effect.

Parameters
streamID a streamID returned by the play() function
leftVolume left volume value (range = 0.0 to 1.0)
rightVolume right volume value (range = 0.0 to 1.0)

public final void stop (int streamID)

Since: API Level 1

Stop a playback stream. Stop the stream specified by the streamID. This is the value returned by the play() function. If the stream is playing, it will be stopped. It also releases any native resources associated with this stream. If the stream is not playing, it will have no effect.

Parameters
streamID a streamID returned by the play() function

public final boolean unload (int soundID)

Since: API Level 1

Unload a sound from a sound ID. Unloads the sound specified by the soundID. This is the value returned by the load() function. Returns true if the sound is successfully unloaded, false if the sound was already unloaded.

Parameters
soundID a soundID returned by the load() function
Returns
  • true if just unloaded, false if previously unloaded

Protected Methods

protected void finalize ()

Since: API Level 1

Is called before the object's memory is being reclaimed by the VM. This can only happen once the VM has detected, during a run of the garbage collector, that the object is no longer reachable by any thread of the running application.

The method can be used to free system resources or perform other cleanup before the object is garbage collected. The default implementation of the method is empty, which is also expected by the VM, but subclasses can override finalize() as required. Uncaught exceptions which are thrown during the execution of this method cause it to terminate immediately but are otherwise ignored.

Note that the VM does guarantee that finalize() is called at most once for any object, but it doesn't guarantee when (if at all) finalize() will be called. For example, object B's finalize() can delay the execution of object A's finalize() method and therefore it can delay the reclamation of A's memory. To be safe, use a ReferenceQueue, because it provides more control over the way the VM deals with references during garbage collection.