Android MediaRecorder调用AudioRecord流程

  通过一个简单的api来看下调用流程，就看MediaRecorder类的setAudioChannels()设置通道数的方法.
废话不多说，直接来看流程.

栗子：
MediaRecorder mRecorder = new MediaRecorder();
mRecorder.setAudioChannels(mChannels);

1.frameworks/base/media/java/android/media/MediaRecorder.java
public void setAudioChannels(int numChannels) {
  setParameter("audio-param-number-of-channels=" + numChannels);
}

private native void setParameter(String nameValuePair);

2.frameworks/base/media/jni/android_media_MediaRecorder.cpp
static void android_media_MediaRecorder_setParameter(JNIEnv *env, jobject thiz, jstring params){
   sp<MediaRecorder> mr = getMediaRecorder(env, thiz);
   process_media_recorder_call(env, mr->setParameters(String8(params8)), "java/lang/RuntimeException", "setParameter failed.");
}

3.
<1>.frameworks/av/include/media/mediarecorder.h
class MediaRecorder : public BnMediaRecorderClient, public virtual IMediaDeathNotifier{
  sp<IMediaRecorder> mMediaRecorder;
}

<2>.frameworks/av/media/libmedia/mediarecorder.cpp
MediaRecorder::MediaRecorder(const String16& opPackageName) : mSurfaceMediaSource(NULL){
   const sp<IMediaPlayerService> service(getMediaPlayerService());
    mMediaRecorder = service->createMediaRecorder(opPackageName);
}

status_t MediaRecorder::setParameters(const String8& params) {
  status_t ret = mMediaRecorder->setParameters(params);
}


4.frameworks/av/media/libmedia/IMediaDeathNotifier.cpp
//Binder通信
<1>.const sp<IMediaPlayerService> IMediaDeathNotifier::getMediaPlayerService(){
   sMediaPlayerService == 0；
   sp<IServiceManager> sm = defaultServiceManager();
   sp<IBinder> binder;
   //此处为代理获取media.player对应的服务
   binder = sm->getService(String16("media.player"));
   sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);
}

<2>.frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp
 void MediaPlayerService::instantiate() {
   //添加media.player字符串对应的MediaPlayerService服务
   defaultServiceManager()->addService(String16("media.player"), new 
   MediaPlayerService());
 }  
}

<3>.frameworks/av/media/mediaserver/main_mediaserver.cpp
int main(int argc __unused, char **argv __unused){
  //启动MediaPlayerService服务
  MediaPlayerService::instantiate();
  ResourceManagerService::instantiate();
  //启动线程池
  ProcessState::self()->startThreadPool();
  //添加到线程池
  IPCThreadState::self()->joinThreadPool();
}

<4>.frameworks/av/media/libmedia/mediarecorder.cpp
接着上边继续追service->createMediaRecorder()
MediaRecorder::MediaRecorder(const String16& opPackageName) : mSurfaceMediaSource(NULL){
   const sp<IMediaPlayerService> service(getMediaPlayerService());
    mMediaRecorder = service->createMediaRecorder(opPackageName);
}


5.frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp
sp<IMediaRecorder> MediaPlayerService::createMediaRecorder(const String16 &opPackageName){
  sp<MediaRecorderClient> recorder = new MediaRecorderClient(this, pid, opPackageName);
  wp<MediaRecorderClient> w = recorder;
  mMediaRecorderClients.add(w);
  return recorder;
}

6.frameworks/av/media/libmediaplayerservice/MediaRecorderClient.cpp
MediaRecorderClient::MediaRecorderClient(const sp<MediaPlayerService>& service, pid_t 
pid, const String16& opPackageName){
  mRecorder = AVMediaServiceFactory::get()->createStagefrightRecorder(opPackageName);
  mMediaPlayerService = service;
}

7.frameworks/av/media/libavextensions/mediaplayerservice/AVMediaServiceFactory.cpp
StagefrightRecorder *AVMediaServiceFactory::createStagefrightRecorder(const String16 
&opPackageName) {
  return new StagefrightRecorder(opPackageName);
}

8.frameworks/av/media/libmediaplayerservice/StagefrightRecorder.cpp
<1>.构造函数
StagefrightRecorder::StagefrightRecorder(const String16 &opPackageName)
    : MediaRecorderBase(opPackageName),
    mWriter(NULL),  mOutputFd(-1), mAudioSource(AUDIO_SOURCE_CNT),
    mVideoSource(VIDEO_SOURCE_LIST_END),mStarted(false)
{
   ALOGV("Constructor");
   reset();
}

注意：所以frameworks/av/media/libmedia/mediarecorder.cpp里的
 mMediaRecorder->setParameters(params);调用的是StagefrightRecorder.cpp里的 
<2>.status_t StagefrightRecorder::setParameters(const String8 &params){
  const char *cparams = params.string();
  const char *key_start = cparams;
  String8 key(key_start, equal_pos - key_start);
  setParameter(key, value)；
}

<3>.status_t StagefrightRecorder::setParameter(const String8 &key, const String8 &value)
{
  //由上文得出,走此分支
  else if (key == "audio-param-number-of-channels") {
        int32_t number_of_channels;
        if (safe_strtoi32(value.string(), &number_of_channels)) {
         return setParamAudioNumberOfChannels(number_of_channels);
        }
    } 
}

<4>.status_t StagefrightRecorder::setParamAudioNumberOfChannels(int32_t channels) {
  mAudioChannels = channels;//将mAudioChannels传出来
}

<5>.sp<MediaCodecSource> StagefrightRecorder::createAudioSource() {
  sp<AudioSource> audioSource = AVFactory::get()->createAudioSource(
                  mAudioSource,
                  mOpPackageName,
                  sourceSampleRate,
                  mAudioChannels,
                  mSampleRate,
                  mClientUid,
                  mClientPid);
}

9.frameworks/av/media/libavextensions/stagefright/AVFactory.cpp
AudioSource* AVFactory::createAudioSource(audio_source_t inputSource,
            const String16 &opPackageName,
            uint32_t sampleRate,
            uint32_t channels,
            uint32_t outSampleRate,
            uid_t clientUid,
            pid_t clientPid) {
    return new AudioSource(inputSource, opPackageName, sampleRate,
                            channels, outSampleRate, clientUid, clientPid);
}

10.frameworks/av/media/libstagefright/AudioSource.cpp
AudioSource::AudioSource( audio_source_t inputSource, const String16 &opPackageName,
       uint32_t sampleRate, uint32_t channelCount, uint32_t outSampleRate,
       uid_t uid, pid_t pid)
{
   status_t status = AudioRecord::getMinFrameCount(&minFrameCount,
                                           sampleRate,
                                           AUDIO_FORMAT_PCM_16_BIT,                                         
                       audio_channel_in_mask_from_count(channelCount));
   
  mRecord = new AudioRecord(
                     inputSource, sampleRate, AUDIO_FORMAT_PCM_16_BIT,
                    audio_channel_in_mask_from_count(channelCount),
                     opPackageName,
                     (size_t) (bufCount * frameCount),
                     AudioRecordCallbackFunction,
                     this,
                    frameCount /*notificationFrames*/,
                    AUDIO_SESSION_ALLOCATE,
                     AudioRecord::TRANSFER_DEFAULT,
                    AUDIO_INPUT_FLAG_NONE,
                    uid,
                    pid);
}

11.frameworks/av/media/libmedia/AudioRecord.cpp
AudioRecord::AudioRecord( audio_source_t inputSource,
        uint32_t sampleRate,
        audio_format_t format,
        audio_channel_mask_t channelMask,
        const String16& opPackageName,
        size_t frameCount,
        callback_t cbf,
        void* user,
        uint32_t notificationFrames,
        audio_session_t sessionId,
        transfer_type transferType,
        audio_input_flags_t flags,
        int uid,
        pid_t pid,
        const audio_attributes_t* pAttributes){
   
   set(inputSource, sampleRate, format, channelMask, frameCount, cbf, user,
             notificationFrames, false /*threadCanCallJava*/, sessionId, transferType, 
flags, uid, pid, pAttributes);
}


今天就到这吧，有时间可以继续往下跟...