Visualizer

ALREADY_EXISTS

public static final int ALREADY_EXISTS

Internal operation status. Not returned by any method.

Constant Value: -2 (0xfffffffe)

ERROR

public static final int ERROR

Unspecified error.

Constant Value: -1 (0xffffffff)

ERROR_BAD_VALUE

public static final int ERROR_BAD_VALUE

Operation failed due to bad parameter value.

Constant Value: -4 (0xfffffffc)

ERROR_DEAD_OBJECT

public static final int ERROR_DEAD_OBJECT

Operation failed due to dead remote object.

Constant Value: -7 (0xfffffff9)

ERROR_INVALID_OPERATION

public static final int ERROR_INVALID_OPERATION

Operation failed because it was requested in wrong state.

Constant Value: -5 (0xfffffffb)

ERROR_NO_INIT

public static final int ERROR_NO_INIT

Operation failed due to bad object initialization.

Constant Value: -3 (0xfffffffd)

ERROR_NO_MEMORY

public static final int ERROR_NO_MEMORY

Operation failed due to lack of memory.

Constant Value: -6 (0xfffffffa)

MEASUREMENT_MODE_NONE

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

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

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

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

public static final int STATE_ENABLED

State of a Visualizer object that is active.

Constant Value: 2 (0x00000002)

STATE_INITIALIZED

public static final int STATE_INITIALIZED

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

Constant Value: 1 (0x00000001)

STATE_UNINITIALIZED

public static final int STATE_UNINITIALIZED

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

Constant Value: 0 (0x00000000)

SUCCESS

public static final int SUCCESS

Successful operation.

Constant Value: 0 (0x00000000)

Visualizer

public Visualizer (int audioSession)

Class constructor.

getCaptureSize

public int getCaptureSize ()

Returns current capture size.

getCaptureSizeRange

public static int[] getCaptureSizeRange ()

Returns the capture size range.

getEnabled

public boolean getEnabled ()

Get current activation state of the visualizer.

getFft

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

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]);
       }

getMaxCaptureRate

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.

getMeasurementMode

public int getMeasurementMode ()

Returns the current measurement modes performed by this audio effect

getMeasurementPeakRms

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.

getSamplingRate

public int getSamplingRate ()

Returns the sampling rate of the captured audio.

getScalingMode

public int getScalingMode ()

Returns the current scaling mode on the captured visualization data.

getWaveForm

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.

release

public void release ()

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

setCaptureSize

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.

setDataCaptureListener

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.

setEnabled

public int setEnabled (boolean enabled)

Enable or disable the visualization engine.

setMeasurementMode

public int setMeasurementMode (int mode)

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

setScalingMode

public int setScalingMode (int mode)

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

finalize

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.