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* Copyright (C) 2010 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <media/AudioEffect.h>
#include <audio_effects/effect_visualizer.h>
#include <string.h>
* 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() method
* - Frequency data: 8-bit magnitude FFT by using the getFft() method
* The length of the capture can be retrieved or specified by calling respectively
* getCaptureSize() and setCaptureSize() methods. Note that the size of the FFT
* is half of the specified capture size but both sides of the spectrum are returned yielding in a
* number of bytes equal to the capture size. The capture size must be a power of 2 in the range
* returned by getMinCaptureSize() and getMaxCaptureSize().
* In addition to the polling capture mode, a callback mode is also available by installing a
* callback function by use of the setCaptureCallBack() method. The rate at which the callback
* is called as well as the type of data returned is specified.
* Before capturing data, the Visualizer must be enabled by calling the setEnabled() method.
* When data capture is not needed any more, the Visualizer should be disabled.
namespace android {
// ----------------------------------------------------------------------------
class Visualizer: public AudioEffect {
enum callback_flags {
CAPTURE_WAVEFORM = 0x00000001, // capture callback returns a PCM wave form
CAPTURE_FFT = 0x00000002, // apture callback returns a frequency representation
CAPTURE_CALL_JAVA = 0x00000004 // the callback thread can call java
/* Constructor.
* See AudioEffect constructor for details on parameters.
Visualizer(int32_t priority = 0,
effect_callback_t cbf = NULL,
void* user = NULL,
int sessionId = 0);
virtual status_t setEnabled(bool enabled);
// maximum capture size in samples
static uint32_t getMaxCaptureSize() { return VISUALIZER_CAPTURE_SIZE_MAX; }
// minimum capture size in samples
static uint32_t getMinCaptureSize() { return VISUALIZER_CAPTURE_SIZE_MIN; }
// maximum capture rate in millihertz
static uint32_t getMaxCaptureRate() { return CAPTURE_RATE_MAX; }
// callback used to return periodic PCM or FFT captures to the application. Either one or both
// types of data are returned (PCM and FFT) according to flags indicated when installing the
// callback. When a type of data is not present, the corresponding size (waveformSize or
// fftSize) is 0.
typedef void (*capture_cbk_t)(void* user,
uint32_t waveformSize,
uint8_t *waveform,
uint32_t fftSize,
uint8_t *fft,
uint32_t samplingrate);
// install a callback to receive periodic captures. The capture rate is specified in milliHertz
// and the capture format is according to flags (see callback_flags).
status_t setCaptureCallBack(capture_cbk_t cbk, void* user, uint32_t flags, uint32_t rate);
// set the capture size capture size must be a power of two in the range
// must be called when the visualizer is not enabled
status_t setCaptureSize(uint32_t size);
uint32_t getCaptureSize() { return mCaptureSize; }
// returns the capture rate indicated when installing the callback
uint32_t getCaptureRate() { return mCaptureRate; }
// returns the sampling rate of the audio being captured
uint32_t getSamplingRate() { return mSampleRate; }
// set the way volume affects the captured data
status_t setScalingMode(uint32_t mode);
uint32_t getScalingMode() { return mScalingMode; }
// return a capture in PCM 8 bit unsigned format. The size of the capture is equal to
// getCaptureSize()
status_t getWaveForm(uint8_t *waveform);
// return a capture in FFT 8 bit signed format. The size of the capture is equal to
// getCaptureSize() but the length of the FFT is half of the size (both parts of the spectrum
// are returned
status_t getFft(uint8_t *fft);
// from IEffectClient
virtual void controlStatusChanged(bool controlGranted);
static const uint32_t CAPTURE_RATE_MAX = 20000;
static const uint32_t CAPTURE_RATE_DEF = 10000;
/* internal class to handle the callback */
class CaptureThread : public Thread
CaptureThread(Visualizer& receiver, uint32_t captureRate, bool bCanCallJava = false);
friend class Visualizer;
virtual bool threadLoop();
virtual status_t readyToRun();
virtual void onFirstRef();
Visualizer& mReceiver;
Mutex mLock;
uint32_t mSleepTimeUs;
status_t doFft(uint8_t *fft, uint8_t *waveform);
void periodicCapture();
uint32_t initCaptureSize();
Mutex mCaptureLock;
uint32_t mCaptureRate;
uint32_t mCaptureSize;
uint32_t mSampleRate;
uint32_t mScalingMode;
capture_cbk_t mCaptureCallBack;
void *mCaptureCbkUser;
sp<CaptureThread> mCaptureThread;
uint32_t mCaptureFlags;
}; // namespace android