关于android电话录音问题的详细分析

1、关于android电话录音问题的详细分析作者：老猫 一直以来都是在网络上看别人的文章，老老实实的做潜水员，今天一时兴起，写点东西，希望对大家有所帮助，不要再走同样的弯路。本文是关于Android下录音问题的分析，网络上都说Android录音时记录下的语音信号都是混音器的信号。但是都没有给出详细说明为什么是这样。我们知道Android下进行电话录音的代码很简单：大致流程如下：recorder = new MediaRecorder();/这里mode可以设置为 VOICE_UPLINK|VOICE_DOWNLINK|VOICE_CALLrecorder.setAudioSource(mode);

2、recorder.setOutputFormat(MediaRecorder.OutputFormat.DEFAULT);recorder.setAudioEncoder(MediaRecorder.AudioEncoder.DEFAULT);recorder.setOutputFile(recFile.getAbsolutePath();/准备录音recorder.prepare();/启动录音recorder.start();/停止录音recorder.stop();MediaRecorder.AudioSource中定义了以下常量可以用于recorder.setAudioSource这里

3、和电话录音相关的有3个常量Voice_call 录制上行线路和下行线路Voice_uplink 录制上行线路，应该是对方的语音Voice_downlink 录制下行线路，应该是我方的语音网络上关于java层如何调用native代码的介绍很多，这里只做简单介绍。JAVA中MediaRecorder的方法会掉用本地C+代码，这些代码编译后为libmedia.so,再通过进程间通信机制Binder和MediaServer通信，MediaServer收到请求后，把这些请求转发给opencore。以下是Android的媒体库框架图，从网络上下载的。从上图可以看出，客户端调用的本地代码位于libmedia

4、.so中，媒体服务进程调用的代码位于libmediaplayerservice.so中。libmediaplayerservice.so再调用底层的libopencoreplayer.so完成具体功能。以下通过代码介绍媒体服务进程如何转发请求到opencore中。关于客户端mediarecorder如何与媒体服务进程交互请搜索网络，这方面文章很多，这里就不多介绍。总而言之，客户端的一个mediarecorder对象和服务器端的MediaRecorderClient对象对应，客户端通过mediarecorder发送的请求，通过进程间通信机制最终都会发送到服务端的MediaRecorderClie

5、nt类中。我们来看下内部类client的声明，代码位于frameworksbasemedialibmediaplayerserviceMediaRecorderClient.hclass MediaRecorderClient : public BnMediaRecorderpublic: virtual status_tsetCamera(const sp<ICamera>& camera); virtual status_t setPreviewSurface(const sp<ISurface>& surface); virtual status_

6、t setVideoSource(int vs); virtual status_t setAudioSource(int as); virtual status_t setOutputFormat(int of); virtual status_t setVideoEncoder(int ve); virtual status_t setAudioEncoder(int ae); virtual status_t setOutputFile(const char* path); virtual status_t setOutputFile(int fd, int64_t offset, in

7、t64_t length); virtual status_t setVideoSize(int width, int height); virtual status_t setVideoFrameRate(int frames_per_second); virtual status_t setParameters(const String8& params); virtual status_t setListener(const sp<IMediaPlayerClient>& listener); virtual status_t prepare(); virtu

8、al status_t getMaxAmplitude(int* max); virtual status_t start(); virtual status_t stop(); virtual status_t reset(); virtual status_t init(); virtual status_t close(); virtual status_t release();。可以看到，大部分客户端方法在MediaRecorderClient中都有对应方法。这样当我们调用客户端的recorder.start();时，最后会调用到MediaRecorderClient类中的start方

9、法。status_t MediaRecorderClient:start() LOGV("start"); Mutex:Autolock lock(mLock); if (mRecorder = NULL) LOGE("recorder is not initialized"); return NO_INIT; return mRecorder->start();/转发给mRecorder /这里的mRecorder是在MediaRecorderClient构造函数中创建的。MediaRecorderClient:MediaRecorderClie

10、nt(const sp<MediaPlayerService>& service, pid_t pid) 。#ifndef NO_OPENCORE /创建了PVMediaRecorder用于录音 mRecorder = new PVMediaRecorder(); #else mRecorder = NULL; #endif mMediaPlayerService = service; 其他的调用也是一样，所有的请求基本都转发给了PVMediaRecorder，这个PVMediaRecorder就是opencore中的对应的录音的类。这样，我们就直接进入opencore分析

11、，先看看PVMediaRecorder的声明，代码位于frameworksbaseincludemediaPVMediaRecorder.h，可以看到，客户端的方法在这里基本都有对应的方法。class PVMediaRecorder : public MediaRecorderBase public: PVMediaRecorder(); virtual PVMediaRecorder(); virtual status_t init(); virtual status_t setAudioSource(audio_source as); virtual status_t setVideoSo

12、urce(video_source vs); virtual status_t setOutputFormat(output_format of); virtual status_t setAudioEncoder(audio_encoder ae); virtual status_t setVideoEncoder(video_encoder ve); virtual status_t setVideoSize(int width, int height); virtual status_t setVideoFrameRate(int frames_per_second); virtual

13、status_t setCamera(const sp<ICamera>& camera); virtual status_t setPreviewSurface(const sp<ISurface>& surface); virtual status_t setOutputFile(const char *path); virtual status_t setOutputFile(int fd, int64_t offset, int64_t length); virtual status_t setParameters(const String8&a

14、mp; params); virtual status_t setListener(const sp<IMediaPlayerClient>& listener); virtual status_t prepare(); virtual status_t start(); virtual status_t stop(); virtual status_t close(); virtual status_t reset(); virtual status_t getMaxAmplitude(int *max);private: status_t doStop(); Autho

15、rDriverWrapper* mAuthorDriverWrapper; PVMediaRecorder(const PVMediaRecorder &); PVMediaRecorder &operator=(const PVMediaRecorder &);Opencore是一个第3方的库，体系比较复杂，关于opencore的详细资料请参阅android源代码树下的externalopencoredoc，网络上也有这方面资料，不过不全。总而言之，Opencore提供了一个多媒体开发框架，要使用Opencore进行多媒体应用，开发人员应该在顶层提供包装接口，在底层提

16、供硬件接口，Opencore提供中间层功能。接收顶层发送的请求，经过处理后，最终交给底层硬件完成任务。在android系统上，顶层和底层代码都位于目录externalopencoreandroid下，其中externalopencoreandroidauthor目录下是关于录音部分的代码。Opencore其他子目录下是原生代码。以下是通过逆向编译后得到的关于录音部分的类模型。这里我们只关注主要部分。PVMediaRecorder类收到的请求都会转发给AuthorDriverWrapper类，AuthorDriverWrapper类收到请求后又会转发给AuthorDriver类，这样，我们只要关

17、注AuthorDriver类就可以了。AuthorDriver中定义了如下的方法： void handleInit(author_command *ac); /#ModelId=4DE0871D000D void handleSetAudioSource(set_audio_source_command *ac); /#ModelId=4DE0871D0010 void handleSetCamera(set_camera_command *ac); /#ModelId=4DE0871D0015 void handleSetVideoSource(set_video_source_comman

18、d *ac); /#ModelId=4DE0871D001C void handleSetOutputFormat(set_output_format_command *ac); /#ModelId=4DE0871D0021 void handleSetAudioEncoder(set_audio_encoder_command *ac); /#ModelId=4DE0871D0024 void handleSetVideoEncoder(set_video_encoder_command *ac); /#ModelId=4DE0871D0029 void handleSetVideoSize

19、(set_video_size_command *ac); /#ModelId=4DE0871D002E void handleSetVideoFrameRate(set_video_frame_rate_command *ac); /#ModelId=4DE0871D0031 void handleSetPreviewSurface(set_preview_surface_command *ac); /#ModelId=4DE0871D0035 void handleSetOutputFile(set_output_file_command *ac); /#ModelId=4DE0871D0

20、03A void handleSetParameters(set_parameters_command *ac); /#ModelId=4DE0871D003D void handlePrepare(author_command *ac); /#ModelId=4DE0871D0042 void handleStart(author_command *ac); /#ModelId=4DE0871D0046 void handleStop(author_command *ac); /#ModelId=4DE0871D004A void handleReset(author_command *ac

21、); /#ModelId=4DE0871D004E void handleClose(author_command *ac); /#ModelId=4DE0871D0052 void handleQuit(author_command *ac);其中每个方法对应于客户端一个请求的处理，这里需要注意的是opencore使用了事件调度机制，这种调度机制在opencore的大部分类中都出现，了解这种机制有助于我们分析代码。简单来说，opencore的大部分类收到一个请求后，会把该请求包装成1个命令对象，然后添加到命令对象队列中，在通过调度对这个命令对象进行处理。通常接收请求的方法名和处理请求的方法名

22、字都有对应关系。比如：status_t PVMediaRecorder:start() LOGV("start"); if (mAuthorDriverWrapper = NULL) LOGE("author driver wrapper is not initialized yet"); return UNKNOWN_ERROR; /把请求包装成命令 author_command *ac = new author_command(AUTHOR_START); if (ac = NULL) LOGE("failed to construct a

23、n author command"); return UNKNOWN_ERROR;/调用mAuthorDriverWrapper的enqueueCommand方法 return mAuthorDriverWrapper->enqueueCommand(ac, 0, 0);status_t AuthorDriverWrapper:enqueueCommand(author_command *ac, media_completion_f comp, void *cookie) if (mAuthorDriver) /再转发给mAuthorDriver return mAuthorD

24、river->enqueueCommand(ac, comp, cookie); return NO_INIT;status_t AuthorDriver:enqueueCommand(author_command *ac, media_completion_f comp, void *cookie)。/把命令请求添加到命令请求队列中mCommandQueue.push_front(ac);。/在opencore调度线程中调用void AuthorDriver:Run()。/调用handleStart处理客户的start请求case AUTHOR_START: handleStart(a

25、c); break;。这样当客户端调用recorder.start()；时，这个请求通过层层转发会调用AuthorDriver的handleStart方法，其他请求也一样，后面就不再列出。void AuthorDriver:handleStart(author_command *ac) LOGV("handleStart");int error = 0;/调用opencore的引擎的start方法 OSCL_TRY(error, mAuthor->Start(ac); OSCL_FIRST_CATCH_ANY(error, commandFailed(ac);mAut

26、hor成员的初始化在AuthorDriver:authorThread()方法中完成。流程图如下，图中Client对象对应于我们的AuthorDriver对象。PVAuthorEngine类定义在文件externalopencoreenginesauthorsrcpvauthorengine.h中其中引擎的start方法定义如下OSCL_EXPORT_REF PVCommandId PVAuthorEngine:Start(const OsclAny* aContextData) PVLOGGER_LOGMSG(PVLOGMSG_INST_LLDBG, iLogger, PVLOGMSG_ST

27、ACK_TRACE, (0, "PVAuthorEngine:Start: aContextData=0x%x", aContextData); PVEngineCommand cmd(PVAE_CMD_START, iCommandId, (OsclAny*)aContextData); Dispatch(cmd); return iCommandId+;经过调度机制由DoStart方法处理该请求PVMFStatus PVAuthorEngine:DoStart(PVEngineCommand& aCmd) PVLOGGER_LOGMSG(PVLOGMSG_INS

28、T_LLDBG, iLogger, PVLOGMSG_STACK_TRACE, (0, "PVAuthorEngine:DoStart"); OSCL_UNUSED_ARG(aCmd); if (GetPVAEState() != PVAE_STATE_INITIALIZED) return PVMFErrInvalidState; iNodeUtil.Start(iComposerNodes); if (iEncoderNodes.size() > 0) iNodeUtil.Start(iEncoderNodes); /调用PVAuthorEngineNodeUti

29、lity的start方法完成请求 iNodeUtil.Start(iDataSourceNodes); return PVMFPending;PVMFStatus PVAuthorEngineNodeUtility:Start(const PVAENodeContainerVector& aNodes, OsclAny* aContext)。 PVAENodeUtilCmd cmd;PVMFStatus status = cmd.Construct(PVAENU_CMD_START, aNodes, aContext);。又是调度机制，由DoStart处理 return AddCmdT

30、oQueue(cmd);PVMFStatus PVAuthorEngineNodeUtility:DoStart(const PVAENodeUtilCmd& aCmd)。 for (uint32 i = 0; i < aCmd.iNodes.size(); i+) nodeContainer = aCmd.iNodesi; nodeContainer->iNode->Start(nodeContainer->iSessionId, aCmd.iContext); );。注意到这里面调用了nodeContainer->iNode->Start(nod

31、eContainer->iSessionId, aCmd.iContext);这个iNode是在调用start函数前面的函数时保存到opencore的引擎中的，具体分析过程比较复杂，这里就不详细列出。总而言之，inode指向PvmfMediaInputNode对象，代码位于externalopencorenodespvmediainputnodesrcpvmf_media_input_node.hOSCL_EXPORT_REF PVMFCommandId PvmfMediaInputNode:Start(PVMFSessionId s, const OsclAny* aContext)

32、PVLOGGER_LOGMSG(PVLOGMSG_INST_LLDBG, iLogger, PVLOGMSG_STACK_TRACE, (0, "PvmfMediaInputNode:Start() called"); PvmfMediaInputNodeCmd cmd; cmd.PvmfMediaInputNodeCmdBase:Construct(s, PVMF_GENERIC_NODE_START, aContext); return QueueCommandL(cmd);通过调度机制又调用了DoStart方法PVMFStatus PvmfMediaInputNode

33、:DoStart(PvmfMediaInputNodeCmd& aCmd)。 /Start the MIOPVMFStatus status = SendMioRequest(aCmd, EStart);。/PVMFStatus PvmfMediaInputNode:SendMioRequest(PvmfMediaInputNodeCmd& aCmd, EMioRequest aRequest) 。 case EStart: OSCL_TRY(err, iMediaIOCmdId = iMediaIOControl->Start(););。调用iMediaIOContro

34、l的start方法，这个iMediaIOControl成员是在创建该节点时候传递近来的，具体分析过程就不说了，太长。总之，iMediaIOControl指向AndroidAudioInput类，还记得我们说过，使用opencore要提供底层接口吗，这个就是android提供的底层接口，代码位于externalopencoreandroidauthorandroid_audio_input.hPVMFCommandId AndroidAudioInput:Start(const OsclAny* aContext) LOGV("Start"); if(iState != ST

35、ATE_INITIALIZED && iState != STATE_PAUSED) LOGE("Start: Invalid state (%d)", iState); OSCL_LEAVE(OsclErrInvalidState); return -1; return AddCmdToQueue(AI_CMD_START, aContext);通过调度机制由DoStart完成/PVMFStatus AndroidAudioInput:DoStart()OsclThread AudioInput_Thread;/创建一个线程，线程入口函数start_aud

36、in_thread_func OsclProcStatus:eOsclProcError ret = AudioInput_Thread.Create( (TOsclThreadFuncPtr)start_audin_thread_func, 0, (TOsclThreadFuncArg)this, Start_on_creation);。int AndroidAudioInput:start_audin_thread_func(TOsclThreadFuncArg arg) prctl(PR_SET_NAME, (unsigned long) "audio in", 0,

37、 0, 0);sp<AndroidAudioInput> obj = (AndroidAudioInput *)arg;/调用audin_thread_func函数 return obj->audin_thread_func();/注意这里创建了一个AudioRecord来完成实际的录音底层工作int AndroidAudioInput:audin_thread_func() / setup audio record session/最后调用的是AudioRecord类完成音频录制 LOGV("create AudioRecord %p", this);

38、AudioRecord * record = new AudioRecord( iAudioSource, iAudioSamplingRate, android:AudioSystem:PCM_16_BIT, (iAudioNumChannels > 1) ? AudioSystem:CHANNEL_IN_STEREO : AudioSystem:CHANNEL_IN_MONO, 4*kBufferSize/iAudioNumChannels/sizeof(int16), flags);。好了，绕了一整圈，我们知道opencore实际上并不负责底层录音的设置，最终工作是由AudioRe

39、cord来完成的，那我们来分析AudioRecord是如何完成录音工作的。AudioRecord类声明在文件frameworksbasemedialibmediaAudioRecord.h中，是audioflinger的一部分。先看下构造函数AudioRecord:AudioRecord( int inputSource, uint32_t sampleRate, int format, uint32_t channels, int frameCount, uint32_t flags, callback_t cbf, void* user, int notificationFrames) :

40、 mStatus(NO_INIT) /调用set方法 mStatus = set(inputSource, sampleRate, format, channels, frameCount, flags, cbf, user, notificationFrames);status_t AudioRecord:set( int inputSource, uint32_t sampleRate, int format, uint32_t channels, int frameCount, uint32_t flags, callback_t cbf, void* user, int notific

41、ationFrames, bool threadCanCallJava)/ input实际上是录音线程句柄，调用AudioSystem:getInput audio_io_handle_t input = AudioSystem:getInput(inputSource, sampleRate, format, channels, (AudioSystem:audio_in_acoustics)flags);10、audiosystem.cppaudio_io_handle_t AudioSystem:getInput(int inputSource, uint32_t samplingRat

42、e, uint32_t format, uint32_t channels, audio_in_acoustics acoustics) const sp<IAudioPolicyService>& aps = AudioSystem:get_audio_policy_service(); if (aps = 0) return 0; return aps->getInput(inputSource, samplingRate, format, channels, acoustics);调用的是AudioPolicyService的getInput，代码位于frame

43、worksbaselibsaudioflingerAudioPolicyService.cppaudio_io_handle_t AudioPolicyService:getInput(int inputSource, uint32_t samplingRate, uint32_t format, uint32_t channels, AudioSystem:audio_in_acoustics acoustics) if (mpPolicyManager = NULL) return 0; Mutex:Autolock _l(mLock);/调用audioPolicyManagerbase的

44、getinput return mpPolicyManager->getInput(inputSource, samplingRate, format, channels, acoustics);audio_io_handle_t AudioPolicyManagerBase:getInput(int inputSource, uint32_t samplingRate, uint32_t format, uint32_t channels, AudioSystem:audio_in_acoustics acoustics) audio_io_handle_t input = 0;/ c

45、ase AUDIO_SOURCE_VOICE_UPLINK:case AUDIO_SOURCE_VOICE_DOWNLINK:case AUDIO_SOURCE_VOICE_CALL:device = AudioSystem:DEVICE_IN_VOICE_CALL;/ 对于电话录音，返回的是DEVICE_IN_VOICE_CALL uint32_t device = getDeviceForInputSource(inputSource); / 设置选择的录音通道，如果是电话录音，设置相应得通道标志 switch(inputSource) case AUDIO_SOURCE_VOICE_UP

46、LINK: channels = AudioSystem:CHANNEL_IN_VOICE_UPLINK; break; case AUDIO_SOURCE_VOICE_DOWNLINK: channels = AudioSystem:CHANNEL_IN_VOICE_DNLINK; break; case AUDIO_SOURCE_VOICE_CALL: channels = (AudioSystem:CHANNEL_IN_VOICE_UPLINK | AudioSystem:CHANNEL_IN_VOICE_DNLINK); break; default: break; /调用AudioP

47、olicyService的openInput input = mpClientInterface->openInput(&inputDesc->mDevice, &inputDesc->mSamplingRate, &inputDesc->mFormat, &inputDesc->mChannels, inputDesc->mAcoustics); return input;audio_io_handle_t AudioPolicyService:openInput(uint32_t *pDevices, uint32_t *

48、pSamplingRate, uint32_t *pFormat, uint32_t *pChannels, uint32_t acoustics) sp<IAudioFlinger> af = AudioSystem:get_audio_flinger(); if (af = 0) LOGW("openInput() could not get AudioFlinger"); return 0; /调用AudioFlinger的openInput return af->openInput(pDevices, pSamplingRate, (uint32_t *)pFormat, pChannels, acoustics);AudioFlinger类定义在frameworksbaselibsaudioflingerAudioFlinger.cpp中int AudioFlinger:openInput(uint32_t *pDevices, uint32_t *pSamplingRate, uint32_t *pFormat, uint32_t