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:
MediaPlayer
or
AudioTrack
using this audio session is visualized Two types of representation of audio content can be captured:
getWaveForm(byte[])
methodgetFft(byte[])
methodThe 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(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
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(MeasurementPeakRms)
.
Nested Classes | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Visualizer.MeasurementPeakRms | A class to store peak and RMS values. | ||||||||||
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, where 0mB is the maximum sample value, and -9600mB is the minimum value. | |||||||||
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 | |||||||||||
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Class constructor.
|
Public Methods | |||||||||||
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Returns current capture size.
| |||||||||||
Returns the capture size range.
| |||||||||||
Get current activation state of the visualizer.
| |||||||||||
Returns a frequency capture of currently playing audio content.
| |||||||||||
Returns the maximum capture rate for the callback capture method.
| |||||||||||
Returns the current measurement modes performed by this audio effect
| |||||||||||
Retrieves the latest peak and RMS measurement.
| |||||||||||
Returns the sampling rate of the captured audio.
| |||||||||||
Returns the current scaling mode on the captured visualization data.
| |||||||||||
Returns a waveform capture of currently playing audio content.
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Releases the native Visualizer resources.
| |||||||||||
Sets the capture size, i.e.
| |||||||||||
Registers an OnDataCaptureListener interface and specifies the rate at which the capture
should be updated as well as the type of capture requested.
| |||||||||||
Enable or disable the visualization engine.
| |||||||||||
Sets the combination of measurement modes to be performed by this audio effect.
| |||||||||||
Set the type of scaling applied on the captured visualization data.
|
Protected Methods | |||||||||||
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Invoked when the garbage collector has detected that this instance is no longer reachable.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
|
Internal operation status. Not returned by any method.
Unspecified error.
Operation failed due to bad parameter value.
Operation failed due to dead remote object.
Operation failed because it was requested in wrong state.
Operation failed due to bad object initialization.
Operation failed due to lack of memory.
Defines a measurement mode in which no measurements are performed.
Defines a measurement mode which computes the peak and RMS value in mB, where 0mB is the
maximum sample value, and -9600mB is the minimum value.
Values for peak and RMS can be retrieved with
getMeasurementPeakRms(MeasurementPeakRms)
.
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.
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.
State of a Visualizer object that is active.
State of a Visualizer object that is ready to be used.
State of a Visualizer object that was not successfully initialized upon creation
Successful operation.
Class constructor.
audioSession | 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. |
---|
java.lang.UnsupportedOperationException | |
RuntimeException | |
UnsupportedOperationException |
Returns the capture size range.
Get current activation state of the visualizer.
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:
Index | 0 | 1 | 2 | 3 | 4 | 5 | ... | n - 2 | n - 1 |
Data | Rf0 | Rf(n/2) | Rf1 | If1 | Rf2 | If2 | ... | Rf(n-1)/2 | If(n-1)/2 |
fft | array of bytes where the FFT should be returned |
---|
SUCCESS
in case of success,
ERROR_NO_MEMORY
, ERROR_INVALID_OPERATION
or ERROR_DEAD_OBJECT
in case of failure.IllegalStateException |
---|
Returns the maximum capture rate for the callback capture method. This is the maximum value
for the rate parameter of the
setDataCaptureListener(OnDataCaptureListener, int, boolean, boolean)
method.
Returns the current measurement modes performed by this audio effect
MEASUREMENT_MODE_NONE
(when no measurements are performed)
or MEASUREMENT_MODE_PEAK_RMS
.IllegalStateException |
---|
Retrieves the latest peak and RMS measurement.
Sets the peak and RMS fields of the supplied Visualizer.MeasurementPeakRms
to the
latest measured values.
measurement | a non-null Visualizer.MeasurementPeakRms instance to store
the measurement values. |
---|
SUCCESS
in case of success, ERROR_BAD_VALUE
,
ERROR_NO_MEMORY
, ERROR_INVALID_OPERATION
or ERROR_DEAD_OBJECT
in case of failure.
Returns the sampling rate of the captured audio.
IllegalStateException |
---|
Returns the current scaling mode on the captured visualization data.
SCALING_MODE_NORMALIZED
and SCALING_MODE_AS_PLAYED
.IllegalStateException |
---|
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.
waveform | array of bytes where the waveform should be returned |
---|
SUCCESS
in case of success,
ERROR_NO_MEMORY
, ERROR_INVALID_OPERATION
or ERROR_DEAD_OBJECT
in case of failure.IllegalStateException |
---|
Releases the native Visualizer resources. It is a good practice to release the visualization engine when not in use.
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.
size | requested capture size |
---|
SUCCESS
in case of success,
ERROR_BAD_VALUE
in case of failure.IllegalStateException |
---|
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.
listener | OnDataCaptureListener registered |
---|---|
rate | rate in milliHertz at which the capture should be updated |
waveform | true if a waveform capture is requested: the onWaveFormDataCapture() method will be called on the OnDataCaptureListener interface. |
fft | true if a frequency capture is requested: the onFftDataCapture() method will be called on the OnDataCaptureListener interface. |
SUCCESS
in case of success,
ERROR_NO_INIT
or ERROR_BAD_VALUE
in case of failure.
Enable or disable the visualization engine.
enabled | requested enable state |
---|
SUCCESS
in case of success,
ERROR_INVALID_OPERATION
or ERROR_DEAD_OBJECT
in case of failure.IllegalStateException |
---|
Sets the combination of measurement modes to be performed by this audio effect.
mode | a mask of the measurements to perform. The valid values are
MEASUREMENT_MODE_NONE (to cancel any measurement)
or MEASUREMENT_MODE_PEAK_RMS . |
---|
SUCCESS
in case of success, ERROR_BAD_VALUE
in case of failure.IllegalStateException |
---|
Set the type of scaling applied on the captured visualization data.
mode | see SCALING_MODE_NORMALIZED
and SCALING_MODE_AS_PLAYED |
---|
SUCCESS
in case of success,
ERROR_BAD_VALUE
in case of failure.IllegalStateException |
---|
Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
Note 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.