目录

Audio系统详解

1       Audio的Framework层功能及用法大全

    1.1        多媒体的framework接口预览

    1.2        Audio相关的文件预览

    1.3        Audio核心

        1.3.1         AudioTrack

        1.3.2         AudioRecord

        1.3.3         AudioFormat

        1.3.4         AudioSystem

    1.4        Audio辅助

        1.4.1         AudioManager和AudioService

        1.4.2         RingToneManager和RingTone

        1.4.3         ToneGenerator

        1.4.4         SoundPool

    1.5        Audio路由

        1.5.1         MediaRounter

    1.6        Audio Framework层总结

2       Audio系统的整体结构

3       Audio系统的Native层

    3.1        Audio框架libmedia

    3.2        AudioFlinger

    3.3        AudioPolicy

        3.3.1         代码位置

        3.3.2         AudioPolicy的结构图

        3.3.3         AudioPolicyManagerBase

        3.3.4         AudioPolicyManagerBase的职责

        3.3.5         AudioPolicyManagerBase中的主要方法

4       Audio系统的Hal层

    4.1        代码位置

 

 

 

 


 

1       Audio的Framework层功能及用法大全

1.1     多媒体的framework接口预览

类型

文件名

描述

多媒体核心

MediaPlayer.java

MediaRecorder.java

应用层控制Extractor，解码

DecoderCapabilities.java 

用来获得Android平台支持的解码器。

EncoderCapabilities.java

用来获得Android平台支持的编码器。

MediaCodecInfo.java

Android4.1

MediaCodec.java

Android4.1

MediaCodecList.java

Android4.1

MediaFormat.java

Android4.1

MediaExtractor.java

Android4.1

Utils

MediaCrypto.java

为MediaCodec提供支持

Android4.1

MediaCryptoException.java

Android4.1

MediaSyncEvent.java

Android4.1

Audio核心

AudioRecord.java

AudioTrack.java

AudioSystem.java

AudioFormat.java

声音路由相关

AudioRoutesInfo.java

用来设置声音路由，现在用户可以自由设置AudioPolicy中的功能了。

Android4.1

MediaRouter.java

Android4.1

Audio辅助及控制

AsyncPlayer.java

声音异步加载

AudioManager.java 

管理音量、铃声

AudioService.java

声音管理服务， AudioManager中调用的是此中的实现

RingtoneManager.java

Ringtone.java

ToneGenerator.java

SoundPool.java

MediaActionSound.java

Android4.1

Camera

CamcorderProfile.java

CameraProfile.java

扫描和Provider

MediaFile.java

MediaScannerClient.java

MediaScannerConnection.java

MediaScanner.java

MediaInserter.java

Metadata.java

TimedText.java

MediaMetadataRetriever.java

MiniThumbFile.java

ThumbnailUtils.java

其它

ExifInterface.java

用来获得Jpeg图像的Exif信息

FaceDetector.java

人脸识别，有没有实现就不知道了,需要再研究。

JetPlayer.java

RemoteControlClient.java

AmrInputStream.java

ResampleInputStream.java

 

说明：在frameworks/base/media/java/android/media/ 路径下总共有57个文件：

文件夹:   2个

aidl文件: 10个

html文件: 1个

以上有说明的文件：44个, 相对Android4.0.3增加了11个。

 

 

下面是两个文件夹下的具体内容：

VideoEditor

    |-- AudioTrack.java

    |-- EffectColor.java

    |-- Effect.java

    |-- EffectKenBurns.java

    |-- ExtractAudioWaveformProgressListener.java

    |-- MediaArtistNativeHelper.java

    |-- MediaImageItem.java

    |-- MediaItem.java

    |-- MediaProperties.java

    |-- MediaVideoItem.java

    |-- OverlayFrame.java

    |-- Overlay.java

    |-- TransitionAlpha.java

    |-- TransitionCrossfade.java

    |-- TransitionFadeBlack.java

    |-- Transition.java

    |-- TransitionSliding.java

    |-- VideoEditorFactory.java

    |-- VideoEditorImpl.java

    |-- VideoEditor.java

    |-- VideoEditorProfile.java

    `-- WaveformData.java

AudioFx

    |-- AcousticEchoCanceler.java

    |-- AudioEffect.java

    |-- AutomaticGainControl.java

    |-- BassBoost.java

    |-- EnvironmentalReverb.java

    |-- Equalizer.java

    |-- NoiseSuppressor.java

    |-- package.html

    |-- PresetReverb.java

    |-- Virtualizer.java

    `-- Visualizer.java

 

1.2     Audio相关的文件预览

在整个Framework的Media部分与Audio相关的部分如下：

类型

文件名

描述

Audio核心

AudioRecord.java

AudioTrack.java

AudioSystem.java

AudioFormat.java

声音路由相关

AudioRoutesInfo.java

用来设置声音路由，现在用户可以自由设置AudioPolicy中的功能了。

Android4.1

MediaRouter.java

Android4.1

Audio辅助及控制

AsyncPlayer.java

声音异步加载

AudioManager.java 

管理音量、铃声

AudioService.java

声音管理服务， AudioManager中调用的是此中的实现

RingtoneManager.java

Ringtone.java

ToneGenerator.java

SoundPool.java

MediaActionSound.java

Android4.1

 

由上图可知：Framework层主要分为两个部分，Audio的核心层和Audio的辅助类。Audio核心层的类包括AudioTrack, AudioRecord, AudioSystem。Audio的辅助类主要有AudioManager，RingToneManager，ToneGenerator和SoundPool。

下面的章节节将分别介绍这些部分。

1.3     Audio核心

1.3.1  AudioTrack

AudioTrack是播放的API接口，具体用法是先new一个实例出来，然后再调用它里边的一个play, write, read等函数， 最后stop, release.

         下图是一个建立及销毁的全过程：

1.3.2  AudioRecord

AudioRecord是录音的API，提供接口给用户调用，并且含有大量的native函数，需要JNI调用Native的相关功能。

1.3.3  AudioFormat

AudioFormat中定义了一些变量，这些变量在AudioTrack和AudioRecord中用到。主要有以下内容：

1.3.3.1 Audio data format

    /** Invalid audio data format */

    public static final int ENCODING_INVALID = 0;

    /** Default audio data format */

    public static final int ENCODING_DEFAULT = 1;

    // These two values must be kept in sync with JNI code for AudioTrack, AudioRecord

    /** Audio data format: PCM 16 bit per sample. Guaranteed to be supported by devices. */

    public static final int ENCODING_PCM_16BIT = 2;

    /** Audio data format: PCM 8 bit per sample. Not guaranteed to be supported by devices. */

    public static final int ENCODING_PCM_8BIT = 3;

1.3.3.2 Chanel mask

包括chanel in 和 chanel out的很多掩码定义

1.3.4  AudioSystem

此类包含了一些常量定义，设备定义，native的方法调用接口等。

以下是代码中的说明:

    /* These values must be kept in sync with AudioSystem.h */

    /*

     * If these are modified, please also update Settings.System.VOLUME_SETTINGS

     * and attrs.xml and AudioManager.java.

     */

    /* The audio stream for phone calls */

1.3.4.1 Audio stream相关

public static final int STREAM_VOICE_CALL = 0;

    public static final int STREAM_SYSTEM = 1;

    public static final int STREAM_RING = 2;

    public static final int STREAM_MUSIC = 3;

    public static final int STREAM_ALARM = 4;

    public static final int STREAM_NOTIFICATION = 5;

    public static final int STREAM_BLUETOOTH_SCO = 6;

    public static final int STREAM_SYSTEM_ENFORCED = 7;

    public static final int STREAM_DTMF = 8;

    public static final int STREAM_TTS = 9;

 

目前一共10种Type, 从0-9, 并且用以下的函数取得StreameType的Count.

// Expose only the getter method publicly so we can change it in the future

    private static final int NUM_STREAM_TYPES = 10;

    public static final int getNumStreamTypes() { return NUM_STREAM_TYPES; }

 

Audio Stream是一个重要的类型，在其它的很多函数中都需要用到它， 如下所示：

public static native boolean isStreamActive(int stream, int inPastMs);

public static native int initStreamVolume(int stream, int indexMin, int indexMax);

public static native int setStreamVolumeIndex(int stream, int index, int device);

public static native int getStreamVolumeIndex(int stream, int device);

public static native int getDevicesForStream(int stream);

 

 

1.3.4.2 Microphone是否静音

public static native int muteMicrophone(boolean on);

public static native boolean isMicrophoneMuted();

 

返回值是 AUDIO_STATUS_OK 或 AUDIO_STATUS_ERROR

1.3.4.3 setPhoneState()

public static native int setPhoneState(int state);

 

// phone state, match audio_mode???

    public static final int PHONE_STATE_OFFCALL = 0;

    public static final int PHONE_STATE_RINGING = 1;

    public static final int PHONE_STATE_INCALL = 2;

上边的被淘汰了，用下边的定义：

/* modes for setPhoneState, must match AudioSystem.h audio_mode */

    public static final int MODE_INVALID            = -2;

    public static final int MODE_CURRENT            = -1;

    public static final int MODE_NORMAL             = 0;

    public static final int MODE_RINGTONE           = 1;

    public static final int MODE_IN_CALL            = 2;

    public static final int MODE_IN_COMMUNICATION   = 3;

    public static final int NUM_MODES               = 4;

 

1.3.4.4 setParameters() 和 getParameters

   

/*

     * Sets a group generic audio configuration parameters. The use of these parameters

     * are platform dependent, see libaudio

     *

     * param keyValuePairs  list of parameters key value pairs in the form:

     *    key1=value1;key2=value2;...

     */

    public static native int setParameters(String keyValuePairs);

 

    /*

     * Gets a group generic audio configuration parameters. The use of these parameters

     * are platform dependent, see libaudio

     *

     * param keys  list of parameters

     * return value: list of parameters key value pairs in the form:

     *    key1=value1;key2=value2;...

     */

public static native String getParameters(String keys);

1.3.4.5 DeviceConnectionState

public static native int setDeviceConnectionState(int device, int state, String device_address);

public static native int getDeviceConnectionState(int device, String device_address);

 

1.3.4.6 ForceUse

    public static native int setForceUse(int usage, int config);

public static native int getForceUse(int usage);

 

// device categories config for setForceUse, must match AudioSystem::forced_config

    public static final int FORCE_NONE = 0;

    public static final int FORCE_SPEAKER = 1;

    public static final int FORCE_HEADPHONES = 2;

    public static final int FORCE_BT_SCO = 3;

    public static final int FORCE_BT_A2DP = 4;

    public static final int FORCE_WIRED_ACCESSORY = 5;

    public static final int FORCE_BT_CAR_DOCK = 6;

    public static final int FORCE_BT_DESK_DOCK = 7;

    public static final int FORCE_ANALOG_DOCK = 8;

    public static final int FORCE_DIGITAL_DOCK = 9;

    public static final int FORCE_NO_BT_A2DP = 10;

    public static final int FORCE_SYSTEM_ENFORCED = 11;

    private static final int NUM_FORCE_CONFIG = 12;

    public static final int FORCE_DEFAULT = FORCE_NONE;

 

// usage for setForceUse, must match AudioSystem::force_use

    public static final int FOR_COMMUNICATION = 0;

    public static final int FOR_MEDIA = 1;

    public static final int FOR_RECORD = 2;

    public static final int FOR_DOCK = 3;

    public static final int FOR_SYSTEM = 4;

    private static final int NUM_FORCE_USE = 5;

 

1.3.4.7 StreamVolume

    public static native int initStreamVolume(int stream, int indexMin, int indexMax);

    public static native int setStreamVolumeIndex(int stream, int index, int device);

    public static native int getStreamVolumeIndex(int stream, int device);

 

1.3.4.8 MasterVolume 和 MasterMute

    public static native int setMasterVolume(float value);

    public static native float getMasterVolume();

    public static native int setMasterMute(boolean mute);

public static native boolean getMasterMute();

 

1.3.4.9 getDevicesForStream()

    public static native int getDevicesForStream(int stream);

 

 

1.3.4.10         PrimaryOutput

    public static native int getPrimaryOutputSamplingRate();

    public static native int getPrimaryOutputFrameCount();

 

1.4     Audio辅助

1.4.1  AudioManager和AudioService

Android中AudioManager主管的是音量及一些铃音等。在代码中的典型用法如下：

        // Request the audio focus so that other apps can pause playback.

final AudioManager audioManager = AudioManager)getSystemService(Context.AUDIO_SERVICE);

audioManager.requestAudioFocus(null, AudioManager.STREAM_MUSIC,

                AudioManager.AUDIOFOCUS_GAIN);

 

得到的AUDIO_SERVICE是AudioManager类型，然后具体的工作再传给AudioService去做。

 

AudioManager提供的具体方法如下：

 

1.4.2  RingToneManager和RingTone

RingToneManager类管理所有的RingTone, 其实际是从数据库中查找出都有哪些Ringtone给调用者，然后调用者可以指定创建哪个RongTone, RongToneManager就会new 相应的RingTone类实例。

RingTone分为三种类型：Ringtone, notifaction, alam.

从其存储的位置还可以分为三种： internel ringtone, media ringtone, drmringtone.

 

RingTone类其实是一个含有StreamType的简单播放器，调用系统的MediaPlayer.

首先尝试用LocalPlayer（类型为MediaPlayer）进行播放设置进来的URI,如果没有LocalPlayer 则用RemotePlayer来进行播放。RemotePlayer是从AudioManager中得来的，即是一个服务中的。

RingTone与Tone音的区别，参见ToneGenerator

1.4.3  ToneGenerator

ToneGenerator的职责是控制简单声音的Tone声发音。 例如电话拨号按键时发出的声音。

ToneGenerator的API也很简单，只是一个构造，然后是StartTone, StopTone.

有一个ToneType的概念。 有很多种Tone类型。

这个ToneGenerator与RingTone不一样， RingTone只是一种概念，其实就是普通的声音文件，比如Mp3， 把它们存到特定的位置，即成为RingTone.这个在扫描的代码中有具体的代码，应该是有三个文件夹的位置。

         ToneGenerator有native层的实现，具体的实现均位于Native层。

1.4.4  SoundPool

SoundPool是为了加快那些短小并且需要频繁播放的声音准备的，例如游戏中的一些发音“哈哈哈，嘿嘿嘿”。

         从它的表面意思就能看出来，声音池，哈哈！！

什么？ 不懂？ 那你知道线程池不？ 也不知道， 那你就别混了……

1.5     Audio路由

1.5.1  MediaRounter

待研究…

1.6     Audio Framework层总结

待研究…

2       Audio系统的整体结构

Audio从整个结构上来说分为Framework层，JNI 层，Native层，Hal及Driver层。

由上节可知，Framework层主要分为两个部分，Audio的核心层和Audio的辅助类。Audio核心层的类包括AudioTrack, AudioRecord, AudioSystem。Audio的辅助类主要有AudioManager，RingToneManager，ToneGenerator和SoundPool。

其中它们之中具有JNI的有：AudioRecorder, AudioTrack, AudioSystem, ToneGenerator, SoundPool。

再之下就是Native层的AudioPolicy和AudioFlinger了。这些内容将会在Native层的部分进行介绍。

下图是整个系统的框架图：

 

从Native层开始，它们的对外接口是libmedia中的AudioTrack, AudioRecorder, AudioSyste, 其中AudioSystem依赖于AudioFlinger和AudioPolicy这两个服务中提供的具体功能。如下图所示：

 

3       Audio系统的Native层

如果按照Android的四层体系架构，Native层（包括）往下是一个完整的体系，Framework层（包括）往上是一个层次，它们分别有它们的对外接口。Framework层的对外接口，请参考第一章，Native层及以下的对外接口就是AudioRecorder, AudioTrack, AudioSyste这三个类。它们之间通过JNI进行联通。

对外接口的三个类：

3.1     Audio框架libmedia

Audio的框架主要是几个对外接口类，及抽象接口定义，比如AudioTrack, AudioSyste, IAudioFlinger，以及AudioPolicyService类的定义。

 

         未完待续…

3.2     AudioFlinger

AudioFlinger是Android中音频的核心，主要负责音频的混音，并把完成的PCM数据送到Hal层的硬件去播放。

 

         未完待续…

 

3.3     AudioPolicy

3.3.1  代码位置

1.       AudioPolicyService位置：

Frameworks/av/services/audioflinger/AudioService.h

Frameworks/av/services/audioflinger/AudioService.cpp

2.       AudioPolicy的头文件定义：

hardware/libhardware/include/hardware/audio_policy.h

3.       实现位置

hardware/libhardware_legacy/audio/audio_policy_hal.cpp

hardware/ libhardware_legacy/audio/AudioPolicyManagerBase.cpp

4.       不同的厂商具有不同的实现从以上Android的实现继承下来。

3.3.2  AudioPolicy的结构图

3.3.3  AudioPolicyManagerBase

可以说AudioPolicyManagerBase是AudioPolicy实现的核心，这是Android的一个默认实现，对于每一个平台来说，产生可以从它继承一个子类，进行自己的定制化修改，但是AudioPolicyManagerBase已经完成了完整的逻辑，一般来说厂商的子类不会重载基类AudioPolicyManagerBase中的实现或者只重载一小部分的内容。

3.3.4  AudioPolicyManagerBase的职责

设置电话的状态

设置Stream的音量，并计算音量，设置到AudioFlinger中。

StartOutput

Forceuse

根据电话状和Stream Type和ForceUse选择device

计算音量时，如果是插着耳机的话，为了保护听力，会降低音量。

3.3.5  AudioPolicyManagerBase中的主要方法

    virtual status_t setDeviceConnectionState(audio_devices_t device,

                                          AudioSystem::device_connection_state state,

                                          const char *device_address) = 0;

    // retrieve a device connection status

    virtual AudioSystem::device_connection_state getDeviceConnectionState(audio_devices_t device,

                                                                          const char *device_address) = 0;

    // indicate a change in phone state. Valid phones states are defined by AudioSystem::audio_mode

    virtual void setPhoneState(int state) = 0;

    // force using a specific device category for the specified usage

    virtual void setForceUse(AudioSystem::force_use usage, AudioSystem::forced_config config) = 0;

    // retrieve current device category forced for a given usage

    virtual AudioSystem::forced_config getForceUse(AudioSystem::force_use usage) = 0;

    // set a system property (e.g. camera sound always audible)

    virtual void setSystemProperty(const char* property, const char* value) = 0;

    // check proper initialization

    virtual status_t initCheck() = 0;

 

    //

    // Audio routing query functions

    //

 

    // request an output appropriate for playback of the supplied stream type and parameters

    virtual audio_io_handle_t getOutput(AudioSystem::stream_type stream,

                                        uint32_t samplingRate = 0,

                                        uint32_t format = AudioSystem::FORMAT_DEFAULT,

                                        uint32_t channels = 0,

                                        AudioSystem::output_flags flags = AudioSystem::OUTPUT_FLAG_INDIRECT) = 0;

    // indicates to the audio policy manager that the output starts being used by corresponding stream.

    virtual status_t startOutput(audio_io_handle_t output,

                                 AudioSystem::stream_type stream,

                                 int session = 0) = 0;

    // indicates to the audio policy manager that the output stops being used by corresponding stream.

    virtual status_t stopOutput(audio_io_handle_t output,

                                AudioSystem::stream_type stream,

                                int session = 0) = 0;

    // releases the output.

    virtual void releaseOutput(audio_io_handle_t output) = 0;

 

    // request an input appropriate for record from the supplied device with supplied parameters.

    virtual audio_io_handle_t getInput(int inputSource,

                                    uint32_t samplingRate = 0,

                                    uint32_t Format = AudioSystem::FORMAT_DEFAULT,

                                    uint32_t channels = 0,

                                    AudioSystem::audio_in_acoustics acoustics = (AudioSystem::audio_in_acoustics)0) = 0;

    // indicates to the audio policy manager that the input starts being used.

    virtual status_t startInput(audio_io_handle_t input) = 0;

    // indicates to the audio policy manager that the input stops being used.

    virtual status_t stopInput(audio_io_handle_t input) = 0;

    // releases the input.

    virtual void releaseInput(audio_io_handle_t input) = 0;

 

    //

    // volume control functions

    //

 

    // initialises stream volume conversion parameters by specifying volume index range.

    virtual void initStreamVolume(AudioSystem::stream_type stream,

                                      int indexMin,

                                      int indexMax) = 0;

 

    // sets the new stream volume at a level corresponding to the supplied index for the

    // supplied device. By convention, specifying AUDIO_DEVICE_OUT_DEFAULT means

    // setting volume for all devices

    virtual status_t setStreamVolumeIndex(AudioSystem::stream_type stream,

                                          int index,

                                          audio_devices_t device) = 0;

 

    // retrieve current volume index for the specified stream and the

    // specified device. By convention, specifying AUDIO_DEVICE_OUT_DEFAULT means

    // querying the volume of the active device.

    virtual status_t getStreamVolumeIndex(AudioSystem::stream_type stream,

                                          int *index,

                                          audio_devices_t device) = 0;

 

    // return the strategy corresponding to a given stream type

    virtual uint32_t getStrategyForStream(AudioSystem::stream_type stream) = 0;

 

    // return the enabled output devices for the given stream type

    virtual audio_devices_t getDevicesForStream(AudioSystem::stream_type stream) = 0;

 

    // Audio effect management

    virtual audio_io_handle_t getOutputForEffect(const effect_descriptor_t *desc) = 0;

    virtual status_t registerEffect(const effect_descriptor_t *desc,

                                    audio_io_handle_t io,

                                    uint32_t strategy,

                                    int session,

                                    int id) = 0;

    virtual status_t unregisterEffect(int id) = 0;

    virtual status_t setEffectEnabled(int id, bool enabled) = 0;

 

    virtual bool isStreamActive(int stream, uint32_t inPastMs = 0) const = 0;

    virtual bool isStreamActiveRemotely(int stream, uint32_t inPastMs = 0) const = 0;

    virtual bool isSourceActive(audio_source_t source) const = 0;

4       Audio系统的Hal层

4.1     代码位置

不同的厂商代码位置不同，但都位于hardware下，以下是intel平台CLV+的代码位置：

hardware/alsa_sound/audio_hw_configurable

其中AudioStreamOutALSA.cpp类是音频输出的实现，如果要dump数据，直接在此类中把数据写到文件中即可， 采用的参数一般来说是， 44100, 16 bit, 双声道。

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