Added in API level 9

Visualizer

open class Visualizer
kotlin.Any
   ↳ 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:

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 android.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

A class to store peak and RMS values.
abstract

The OnDataCaptureListener interface defines methods called by the Visualizer to periodically update the audio visualization capture.
Constants
static Int

Internal operation status.
static Int

Unspecified error.
static Int

Operation failed due to bad parameter value.
static Int

Operation failed due to dead remote object.
static Int

Operation failed because it was requested in wrong state.
static Int

Operation failed due to bad object initialization.
static Int

Operation failed due to lack of memory.
static Int

Defines a measurement mode in which no measurements are performed.
static Int

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).
static Int

Defines a capture mode where the playback volume will affect (scale) the range of the captured data.
static Int

Defines a capture mode where amplification is applied based on the content of the captured data.
static Int

State of a Visualizer object that is active.
static Int

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

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

Successful operation.
Public constructors
Visualizer(audioSession: Int)

Class constructor.
Public methods
open Int

Returns current capture size.
open static IntArray!

Returns the capture size range.
open Boolean

Get current activation state of the visualizer.
open Int

Returns a frequency capture of currently playing audio content.
open static Int

Returns the maximum capture rate for the callback capture method.
open Int

Returns the current measurement modes performed by this audio effect
open Int

Retrieves the latest peak and RMS measurement.
open Int

Returns the sampling rate of the captured audio.
open Int

Returns the current scaling mode on the captured visualization data.
open Int
getWaveForm(waveform: ByteArray!)

Returns a waveform capture of currently playing audio content.
open Unit

Releases the native Visualizer resources.
open Int

Sets the capture size, i.
open Int

Registers an OnDataCaptureListener interface and specifies the rate at which the capture should be updated as well as the type of capture requested.
open Int
setEnabled(enabled: Boolean)

Enable or disable the visualization engine.
open Int

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

Set the type of scaling applied on the captured visualization data.
Protected methods
open Unit

Constants

ALREADY_EXISTS

Added in API level 9
static val ALREADY_EXISTS: Int

Internal operation status. Not returned by any method.

Value: -2

ERROR

Added in API level 9
static val ERROR: Int

Unspecified error.

Value: -1

ERROR_BAD_VALUE

Added in API level 9
static val ERROR_BAD_VALUE: Int

Operation failed due to bad parameter value.

Value: -4

ERROR_DEAD_OBJECT

Added in API level 9
static val ERROR_DEAD_OBJECT: Int

Operation failed due to dead remote object.

Value: -7

ERROR_INVALID_OPERATION

Added in API level 9
static val ERROR_INVALID_OPERATION: Int

Operation failed because it was requested in wrong state.

Value: -5

ERROR_NO_INIT

Added in API level 9
static val ERROR_NO_INIT: Int

Operation failed due to bad object initialization.

Value: -3

ERROR_NO_MEMORY

Added in API level 9
static val ERROR_NO_MEMORY: Int

Operation failed due to lack of memory.

Value: -6

MEASUREMENT_MODE_NONE

Added in API level 19
static val MEASUREMENT_MODE_NONE: Int

Defines a measurement mode in which no measurements are performed.

Value: 0

MEASUREMENT_MODE_PEAK_RMS

Added in API level 19
static val MEASUREMENT_MODE_PEAK_RMS: Int

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.

Value: 1

SCALING_MODE_AS_PLAYED

Added in API level 16
static val SCALING_MODE_AS_PLAYED: Int

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.

Value: 1

SCALING_MODE_NORMALIZED

Added in API level 16
static val SCALING_MODE_NORMALIZED: Int

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.

Value: 0

STATE_ENABLED

Added in API level 9
static val STATE_ENABLED: Int

State of a Visualizer object that is active.

Value: 2

STATE_INITIALIZED

Added in API level 9
static val STATE_INITIALIZED: Int

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

Value: 1

STATE_UNINITIALIZED

Added in API level 9
static val STATE_UNINITIALIZED: Int

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

Value: 0

SUCCESS

Added in API level 9
static val SUCCESS: Int

Successful operation.

Value: 0

Public constructors

Visualizer

Added in API level 9
Visualizer(audioSession: Int)

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.
Exceptions
java.lang.UnsupportedOperationException
java.lang.RuntimeException

Public methods

getCaptureSize

Added in API level 9
open fun getCaptureSize(): Int

Returns current capture size.

Return
Int the capture size in bytes.

getCaptureSizeRange

Added in API level 9
open static fun getCaptureSizeRange(): IntArray!

Returns the capture size range.

Return
IntArray! the mininum capture size is returned in first array element and the maximum in second array element.

getEnabled

Added in API level 9
open fun getEnabled(): Boolean

Get current activation state of the visualizer.

Return
Boolean true if the visualizer is active, false otherwise

getFft

Added in API level 9
open fun getFft(fft: ByteArray!): Int

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 ByteArray!: array of bytes where the FFT should be returned
Return
Int SUCCESS in case of success, ERROR_NO_MEMORY, ERROR_INVALID_OPERATION or ERROR_DEAD_OBJECT in case of failure.
Exceptions
java.lang.IllegalStateException

getMaxCaptureRate

Added in API level 9
open static fun getMaxCaptureRate(): Int

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.

Return
Int the maximum capture rate expressed in milliHertz

getMeasurementMode

Added in API level 19
open fun getMeasurementMode(): Int

Returns the current measurement modes performed by this audio effect

Return
Int the mask of the measurements, MEASUREMENT_MODE_NONE (when no measurements are performed) or MEASUREMENT_MODE_PEAK_RMS.
Exceptions
java.lang.IllegalStateException

getMeasurementPeakRms

Added in API level 19
open fun getMeasurementPeakRms(measurement: Visualizer.MeasurementPeakRms!): Int

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.
Return
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
open fun getSamplingRate(): Int

Returns the sampling rate of the captured audio.

Return
Int the sampling rate in milliHertz.

getScalingMode

Added in API level 16
open fun getScalingMode(): Int

Returns the current scaling mode on the captured visualization data.

Return
Int the scaling mode, see SCALING_MODE_NORMALIZED and SCALING_MODE_AS_PLAYED.
Exceptions
java.lang.IllegalStateException

getWaveForm

Added in API level 9
open fun getWaveForm(waveform: ByteArray!): Int

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 ByteArray!: array of bytes where the waveform should be returned, array length must be at least equals to the capture size returned by getCaptureSize().
Return
Int SUCCESS in case of success, ERROR_NO_MEMORY, ERROR_INVALID_OPERATION or ERROR_DEAD_OBJECT in case of failure.
Exceptions
java.lang.IllegalStateException
java.lang.IllegalArgumentException

release

Added in API level 9
open fun release(): Unit

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
open fun setCaptureSize(size: Int): Int

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
Return
Int SUCCESS in case of success, ERROR_INVALID_OPERATION if Visualizer effect enginer not enabled.
Exceptions
java.lang.IllegalStateException if the effect is not in proper state.
java.lang.IllegalArgumentException if the size parameter is invalid (out of supported range).

setDataCaptureListener

Added in API level 9
open fun setDataCaptureListener(
    listener: Visualizer.OnDataCaptureListener?, 
    rate: Int, 
    waveform: Boolean, 
    fft: Boolean
): Int

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.
Return
Int SUCCESS in case of success, ERROR_NO_INIT or ERROR_BAD_VALUE in case of failure.

setEnabled

Added in API level 9
open fun setEnabled(enabled: Boolean): Int

Enable or disable the visualization engine.

Parameters
enabled Boolean: requested enable state
Return
Int SUCCESS in case of success, ERROR_INVALID_OPERATION or ERROR_DEAD_OBJECT in case of failure.
Exceptions
java.lang.IllegalStateException

setMeasurementMode

Added in API level 19
open fun setMeasurementMode(mode: Int): Int

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.
Return
Int SUCCESS in case of success, ERROR_BAD_VALUE in case of failure.
Exceptions
java.lang.IllegalStateException

setScalingMode

Added in API level 16
open fun setScalingMode(mode: Int): Int

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

Parameters
mode Int: see SCALING_MODE_NORMALIZED and SCALING_MODE_AS_PLAYED
Return
Int SUCCESS in case of success, ERROR_BAD_VALUE in case of failure.
Exceptions
java.lang.IllegalStateException

Protected methods

finalize

Added in API level 9
protected open fun finalize(): Unit
Exceptions
java.lang.Throwable the Exception raised by this method