Added in API level 9

Visualizer

Kotlin |Java

public class Visualizer
extends Object

java.lang.Object
↳	android.media.audiofx.Visualizer

The Visualizer class enables application to retrieve part of the currently playing audio for visualization purpose. It is not an audio recording interface and only returns partial and low quality audio content. However, to protect privacy of certain audio data (e.g voice mail) the use of the visualizer requires the permission android.permission.RECORD_AUDIO.

The audio session ID passed to the constructor indicates which audio content should be visualized:

If the session is 0, the audio output mix is visualized
If the session is not 0, the audio from a particular MediaPlayer or AudioTrack using this audio session is visualized

Two types of representation of audio content can be captured:

Waveform data: consecutive 8-bit (unsigned) mono samples by using the getWaveForm(byte[]) method
Frequency data: 8-bit magnitude FFT by using the getFft(byte[]) method

The length of the capture can be retrieved or specified by calling respectively getCaptureSize() and setCaptureSize(int) methods. The capture size must be a power of 2 in the range returned by getCaptureSizeRange().

In addition to the polling capture mode described above with getWaveForm(byte[]) and getFft(byte[]) methods, a callback mode is also available by installing a listener by use of the setDataCaptureListener(android.media.audiofx.Visualizer.OnDataCaptureListener, int, boolean, boolean) method. The rate at which the listener capture method is called as well as the type of data returned is specified.

Before capturing data, the Visualizer must be enabled by calling the setEnabled(boolean) method. When data capture is not needed any more, the Visualizer should be disabled.

It is good practice to call the release() method when the Visualizer is not used anymore to free up native resources associated to the Visualizer instance.

Creating a Visualizer on the output mix (audio session 0) requires permission Manifest.permission.MODIFY_AUDIO_SETTINGS

The Visualizer class can also be used to perform measurements on the audio being played back. The measurements to perform are defined by setting a mask of the requested measurement modes with setMeasurementMode(int). Supported values are MEASUREMENT_MODE_NONE to cancel any measurement, and MEASUREMENT_MODE_PEAK_RMS for peak and RMS monitoring. Measurements can be retrieved through getMeasurementPeakRms(android.media.audiofx.Visualizer.MeasurementPeakRms).

Summary

Nested classes
`class`	`Visualizer.MeasurementPeakRms` A class to store peak and RMS values.
`interface`	`Visualizer.OnDataCaptureListener` The OnDataCaptureListener interface defines methods called by the Visualizer to periodically update the audio visualization capture.

Constants
`int`	`ALREADY_EXISTS` Internal operation status.
`int`	`ERROR` Unspecified error.
`int`	`ERROR_BAD_VALUE` Operation failed due to bad parameter value.
`int`	`ERROR_DEAD_OBJECT` Operation failed due to dead remote object.
`int`	`ERROR_INVALID_OPERATION` Operation failed because it was requested in wrong state.
`int`	`ERROR_NO_INIT` Operation failed due to bad object initialization.
`int`	`ERROR_NO_MEMORY` Operation failed due to lack of memory.
`int`	`MEASUREMENT_MODE_NONE` Defines a measurement mode in which no measurements are performed.
`int`	`MEASUREMENT_MODE_PEAK_RMS` Defines a measurement mode which computes the peak and RMS value in mB below the "full scale", where 0mB is normally the maximum sample value (but see the note below).
`int`	`SCALING_MODE_AS_PLAYED` Defines a capture mode where the playback volume will affect (scale) the range of the captured data.
`int`	`SCALING_MODE_NORMALIZED` Defines a capture mode where amplification is applied based on the content of the captured data.
`int`	`STATE_ENABLED` State of a Visualizer object that is active.
`int`	`STATE_INITIALIZED` State of a Visualizer object that is ready to be used.
`int`	`STATE_UNINITIALIZED` State of a Visualizer object that was not successfully initialized upon creation
`int`	`SUCCESS` Successful operation.

Public constructors
`Visualizer(int audioSession)` Class constructor.

Public methods
`int`	`getCaptureSize()` Returns current capture size.
`static int[]`	`getCaptureSizeRange()` Returns the capture size range.
`boolean`	`getEnabled()` Get current activation state of the visualizer.
`int`	`getFft(byte[] fft)` Returns a frequency capture of currently playing audio content.
`static int`	`getMaxCaptureRate()` Returns the maximum capture rate for the callback capture method.
`int`	`getMeasurementMode()` Returns the current measurement modes performed by this audio effect
`int`	`getMeasurementPeakRms(Visualizer.MeasurementPeakRms measurement)` Retrieves the latest peak and RMS measurement.
`int`	`getSamplingRate()` Returns the sampling rate of the captured audio.
`int`	`getScalingMode()` Returns the current scaling mode on the captured visualization data.
`int`	`getWaveForm(byte[] waveform)` Returns a waveform capture of currently playing audio content.
`void`	`release()` Releases the native Visualizer resources.
`int`	`setCaptureSize(int size)` Sets the capture size, i.e.
`int`	`setDataCaptureListener(Visualizer.OnDataCaptureListener listener, int rate, boolean waveform, boolean fft)` Registers an OnDataCaptureListener interface and specifies the rate at which the capture should be updated as well as the type of capture requested.
`int`	`setEnabled(boolean enabled)` Enable or disable the visualization engine.
`int`	`setMeasurementMode(int mode)` Sets the combination of measurement modes to be performed by this audio effect.
`int`	`setScalingMode(int mode)` Set the type of scaling applied on the captured visualization data.

Protected methods
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Constants

ALREADY_EXISTS

Added in API level 9

public static final int ALREADY_EXISTS

Internal operation status. Not returned by any method.

Constant Value: -2 (0xfffffffe)

ERROR

Added in API level 9

public static final int ERROR

Unspecified error.

Constant Value: -1 (0xffffffff)

ERROR_BAD_VALUE

Added in API level 9

public static final int ERROR_BAD_VALUE

Operation failed due to bad parameter value.

Constant Value: -4 (0xfffffffc)

ERROR_DEAD_OBJECT

Added in API level 9

public static final int ERROR_DEAD_OBJECT

Operation failed due to dead remote object.

Constant Value: -7 (0xfffffff9)

ERROR_INVALID_OPERATION

Added in API level 9

public static final int ERROR_INVALID_OPERATION

Operation failed because it was requested in wrong state.

Constant Value: -5 (0xfffffffb)

ERROR_NO_INIT

Added in API level 9

public static final int ERROR_NO_INIT

Operation failed due to bad object initialization.

Constant Value: -3 (0xfffffffd)

ERROR_NO_MEMORY

Added in API level 9

public static final int ERROR_NO_MEMORY

Operation failed due to lack of memory.

Constant Value: -6 (0xfffffffa)

MEASUREMENT_MODE_NONE

Added in API level 19

public static final int MEASUREMENT_MODE_NONE

Defines a measurement mode in which no measurements are performed.

Constant Value: 0 (0x00000000)

MEASUREMENT_MODE_PEAK_RMS

Added in API level 19

public static final int MEASUREMENT_MODE_PEAK_RMS

Defines a measurement mode which computes the peak and RMS value in mB below the "full scale", where 0mB is normally the maximum sample value (but see the note below). Minimum value depends on the resolution of audio samples used by the audio framework. The value of -9600mB is the minimum value for 16-bit audio systems and -14400mB or below for "high resolution" systems. Values for peak and RMS can be retrieved with getMeasurementPeakRms(android.media.audiofx.Visualizer.MeasurementPeakRms).

Note: when Visualizer effect is attached to the global session (with session ID 0), it is possible to observe RMS peaks higher than 0 dBFS, for example in the case when there are multiple audio sources playing simultaneously. In this case getMeasurementPeakRms(android.media.audiofx.Visualizer.MeasurementPeakRms) method can return a positive value.

Constant Value: 1 (0x00000001)

SCALING_MODE_AS_PLAYED

Added in API level 16

public static final int SCALING_MODE_AS_PLAYED

Defines a capture mode where the playback volume will affect (scale) the range of the captured data. A low playback volume will lead to low sample and fft values, and vice-versa.

Constant Value: 1 (0x00000001)

SCALING_MODE_NORMALIZED

Added in API level 16

public static final int SCALING_MODE_NORMALIZED

Defines a capture mode where amplification is applied based on the content of the captured data. This is the default Visualizer mode, and is suitable for music visualization.

Constant Value: 0 (0x00000000)

STATE_ENABLED

Added in API level 9

public static final int STATE_ENABLED

State of a Visualizer object that is active.

Constant Value: 2 (0x00000002)

STATE_INITIALIZED

Added in API level 9

public static final int STATE_INITIALIZED

State of a Visualizer object that is ready to be used.

Constant Value: 1 (0x00000001)

STATE_UNINITIALIZED

Added in API level 9

public static final int STATE_UNINITIALIZED

State of a Visualizer object that was not successfully initialized upon creation

Constant Value: 0 (0x00000000)

SUCCESS

Added in API level 9

public static final int SUCCESS

Successful operation.

Constant Value: 0 (0x00000000)

Public constructors

Visualizer

Added in API level 9

public Visualizer (int audioSession)

Class constructor.

Parameters
`audioSession`	`int`: system wide unique audio session identifier. If audioSession is not 0, the visualizer will be attached to the MediaPlayer or AudioTrack in the same audio session. Otherwise, the Visualizer will apply to the output mix.

Throws
	java.lang.UnsupportedOperationException
	java.lang.RuntimeException
`RuntimeException`
`UnsupportedOperationException`

Public methods

getCaptureSize

Added in API level 9

public int getCaptureSize ()

Returns current capture size.

Returns
`int`	the capture size in bytes.

Throws
`IllegalStateException`

getCaptureSizeRange

Added in API level 9

public static int[] getCaptureSizeRange ()

Returns the capture size range.

Returns
`int[]`	the mininum capture size is returned in first array element and the maximum in second array element.

getEnabled

Added in API level 9

public boolean getEnabled ()

Get current activation state of the visualizer.

Returns
`boolean`	true if the visualizer is active, false otherwise

getFft

Added in API level 9

public int getFft (byte[] fft)

Returns a frequency capture of currently playing audio content.

This method must be called when the Visualizer is enabled.

The capture is an 8-bit magnitude FFT, the frequency range covered being 0 (DC) to half of the sampling rate returned by getSamplingRate(). The capture returns the real and imaginary parts of a number of frequency points equal to half of the capture size plus one.

Note: only the real part is returned for the first point (DC) and the last point (sampling frequency / 2).

The layout in the returned byte array is as follows:

n is the capture size returned by getCaptureSize()
Rfk, Ifk are respectively the real and imaginary parts of the kth frequency component
If Fs is the sampling frequency retuned by getSamplingRate() the kth frequency is: k * Fs / n

Index	0	1	2	3	4	5	...	n - 2	n - 1
Data	Rf0	Rf(n/2)	Rf1	If1	Rf2	If2	...	Rf(n/2-1)	If(n/2-1)

In order to obtain magnitude and phase values the following code can be used:

       int n = fft.size();
       float[] magnitudes = new float[n / 2 + 1];
       float[] phases = new float[n / 2 + 1];
       magnitudes[0] = (float)Math.abs(fft[0]);      // DC
       magnitudes[n / 2] = (float)Math.abs(fft[1]);  // Nyquist
       phases[0] = phases[n / 2] = 0;
       for (int k = 1; k < n / 2; k++) {
           int i = k * 2;
           magnitudes[k] = (float)Math.hypot(fft[i], fft[i + 1]);
           phases[k] = (float)Math.atan2(fft[i + 1], fft[i]);
       }

Parameters
`fft`	`byte`: array of bytes where the FFT should be returned

Returns
`int`	`SUCCESS` in case of success, `ERROR_NO_MEMORY`, `ERROR_INVALID_OPERATION` or `ERROR_DEAD_OBJECT` in case of failure.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

getMaxCaptureRate

Added in API level 9

public static int getMaxCaptureRate ()

Returns the maximum capture rate for the callback capture method. This is the maximum value for the rate parameter of the setDataCaptureListener(android.media.audiofx.Visualizer.OnDataCaptureListener, int, boolean, boolean) method.

Returns
`int`	the maximum capture rate expressed in milliHertz

getMeasurementMode

Added in API level 19

public int getMeasurementMode ()

Returns the current measurement modes performed by this audio effect

Returns
`int`	the mask of the measurements, `MEASUREMENT_MODE_NONE` (when no measurements are performed) or `MEASUREMENT_MODE_PEAK_RMS`.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

getMeasurementPeakRms

Added in API level 19

public int getMeasurementPeakRms (Visualizer.MeasurementPeakRms measurement)

Retrieves the latest peak and RMS measurement. Sets the peak and RMS fields of the supplied Visualizer.MeasurementPeakRms to the latest measured values.

Parameters
`measurement`	`Visualizer.MeasurementPeakRms`: a non-null `Visualizer.MeasurementPeakRms` instance to store the measurement values.

Returns
`int`	`SUCCESS` in case of success, `ERROR_BAD_VALUE`, `ERROR_NO_MEMORY`, `ERROR_INVALID_OPERATION` or `ERROR_DEAD_OBJECT` in case of failure.

getSamplingRate

Added in API level 9

public int getSamplingRate ()

Returns the sampling rate of the captured audio.

Returns
`int`	the sampling rate in milliHertz.

Throws
`IllegalStateException`

getScalingMode

Added in API level 16

public int getScalingMode ()

Returns the current scaling mode on the captured visualization data.

Returns
`int`	the scaling mode, see `SCALING_MODE_NORMALIZED` and `SCALING_MODE_AS_PLAYED`.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

getWaveForm

Added in API level 9

public int getWaveForm (byte[] waveform)

Returns a waveform capture of currently playing audio content. The capture consists in a number of consecutive 8-bit (unsigned) mono PCM samples equal to the capture size returned by getCaptureSize().

This method must be called when the Visualizer is enabled.

Parameters
`waveform`	`byte`: array of bytes where the waveform should be returned, array length must be at least equals to the capture size returned by `getCaptureSize()`.

Returns
`int`	`SUCCESS` in case of success, `ERROR_NO_MEMORY`, `ERROR_INVALID_OPERATION` or `ERROR_DEAD_OBJECT` in case of failure.

Throws
	java.lang.IllegalStateException
	java.lang.IllegalArgumentException
`IllegalStateException`

release

Added in API level 9

public void release ()

Releases the native Visualizer resources. It is a good practice to release the visualization engine when not in use.

setCaptureSize

Added in API level 9

public int setCaptureSize (int size)

Sets the capture size, i.e. the number of bytes returned by getWaveForm(byte[]) and getFft(byte[]) methods. The capture size must be a power of 2 in the range returned by getCaptureSizeRange(). This method must not be called when the Visualizer is enabled.

Parameters
`size`	`int`: requested capture size

Returns
`int`	`SUCCESS` in case of success, `ERROR_INVALID_OPERATION` if Visualizer effect enginer not enabled.

Throws
`IllegalStateException`	if the effect is not in proper state.
`IllegalArgumentException`	if the size parameter is invalid (out of supported range).

setDataCaptureListener

Added in API level 9

public int setDataCaptureListener (Visualizer.OnDataCaptureListener listener, 
                int rate, 
                boolean waveform, 
                boolean fft)

Registers an OnDataCaptureListener interface and specifies the rate at which the capture should be updated as well as the type of capture requested.

Call this method with a null listener to stop receiving the capture updates.

Parameters
`listener`	`Visualizer.OnDataCaptureListener`: OnDataCaptureListener registered This value may be `null`.
`rate`	`int`: rate in milliHertz at which the capture should be updated
`waveform`	`boolean`: true if a waveform capture is requested: the onWaveFormDataCapture() method will be called on the OnDataCaptureListener interface.
`fft`	`boolean`: true if a frequency capture is requested: the onFftDataCapture() method will be called on the OnDataCaptureListener interface.

Returns
`int`	`SUCCESS` in case of success, `ERROR_NO_INIT` or `ERROR_BAD_VALUE` in case of failure.

setEnabled

Added in API level 9

public int setEnabled (boolean enabled)

Enable or disable the visualization engine.

Parameters
`enabled`	`boolean`: requested enable state

Returns
`int`	`SUCCESS` in case of success, `ERROR_INVALID_OPERATION` or `ERROR_DEAD_OBJECT` in case of failure.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

setMeasurementMode

Added in API level 19

public int setMeasurementMode (int mode)

Sets the combination of measurement modes to be performed by this audio effect.

Parameters
`mode`	`int`: a mask of the measurements to perform. The valid values are `MEASUREMENT_MODE_NONE` (to cancel any measurement) or `MEASUREMENT_MODE_PEAK_RMS`.

Returns
`int`	`SUCCESS` in case of success, `ERROR_BAD_VALUE` in case of failure.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

setScalingMode

Added in API level 16

public int setScalingMode (int mode)

Set the type of scaling applied on the captured visualization data.

Parameters
`mode`	`int`: see `SCALING_MODE_NORMALIZED` and `SCALING_MODE_AS_PLAYED`

Returns
`int`	`SUCCESS` in case of success, `ERROR_BAD_VALUE` in case of failure.

Throws
	java.lang.IllegalStateException
`IllegalStateException`

Protected methods

finalize

Added in API level 9

protected void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Visualizer

Summary

Nested classes

Constants

Public constructors

Public methods

Protected methods

Inherited methods

Constants

ALREADY_EXISTS

ERROR

ERROR_BAD_VALUE

ERROR_DEAD_OBJECT

ERROR_INVALID_OPERATION

ERROR_NO_INIT

ERROR_NO_MEMORY

MEASUREMENT_MODE_NONE

MEASUREMENT_MODE_PEAK_RMS

SCALING_MODE_AS_PLAYED

SCALING_MODE_NORMALIZED

STATE_ENABLED

STATE_INITIALIZED

STATE_UNINITIALIZED

SUCCESS

Public constructors

Visualizer

Public methods

getCaptureSize

getCaptureSizeRange

getEnabled

getFft

getMaxCaptureRate

getMeasurementMode

getMeasurementPeakRms

getSamplingRate

getScalingMode

getWaveForm

release

setCaptureSize

setDataCaptureListener

setEnabled

setMeasurementMode

setScalingMode

Protected methods

finalize