Audio播放流程(三)---NuPlayer流程之setAudioStreamType以及prepare

1.setAudioStreamType的过程

frameworks\av\media\libmediaplayerservice\MediaPlayerService.cpp

status_t MediaPlayerService::Client::setAudioStreamType(audio_stream_type_t type)
{ALOGE("[%d] setAudioStreamType(%d)", mConnId, type);// TODO: for hardware output, call player insteadMutex::Autolock l(mLock);if (mAudioOutput != 0) mAudioOutput->setAudioStreamType(type);return NO_ERROR;
}

这里的mAudioOutput是在Audio播放流程(二)—MediaPlayerService流程之setDataSource中创建的。

setDataSource_premAudioOutput = new AudioOutput(...)将AudioOutput设置为NuPlayer的Sink端static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);

继续

void MediaPlayerService::AudioOutput::setAudioStreamType(audio_stream_type_t streamType)
{Mutex::Autolock lock(mLock);// do not allow direct stream type modification if attributes have been setif (mAttributes == NULL) {mStreamType = streamType;// No attributes are set, for mediaPlayer playback, force populate attributes// This is done to ensure that we qualify for a direct outputmAttributes = (audio_attributes_t *) calloc(1, sizeof(audio_attributes_t));if (mAttributes != NULL) {stream_type_to_audio_attributes(mStreamType, mAttributes);}}
}
...
static void stream_type_to_audio_attributes(audio_stream_type_t streamType,audio_attributes_t *attr) {memset(attr, 0, sizeof(audio_attributes_t));switch (streamType) {case AUDIO_STREAM_DEFAULT:case AUDIO_STREAM_MUSIC:attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;attr->usage = AUDIO_USAGE_MEDIA;break;case AUDIO_STREAM_VOICE_CALL:attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;break;case AUDIO_STREAM_ENFORCED_AUDIBLE:attr->flags  |= AUDIO_FLAG_AUDIBILITY_ENFORCED;// intended fall through, attributes in common with STREAM_SYSTEMcase AUDIO_STREAM_SYSTEM:attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;attr->usage = AUDIO_USAGE_ASSISTANCE_SONIFICATION;break;case AUDIO_STREAM_RING:attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;attr->usage = AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE;break;case AUDIO_STREAM_ALARM:attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;attr->usage = AUDIO_USAGE_ALARM;break;case AUDIO_STREAM_NOTIFICATION:attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;attr->usage = AUDIO_USAGE_NOTIFICATION;break;case AUDIO_STREAM_BLUETOOTH_SCO:attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;attr->flags |= AUDIO_FLAG_SCO;break;case AUDIO_STREAM_DTMF:attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING;break;case AUDIO_STREAM_TTS:attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;attr->usage = AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY;break;default:ALOGE("invalid stream type %d when converting to attributes", streamType);}
}

这个API还是很简单的，就是设置音频的属性，例如：

case AUDIO_STREAM_MUSIC:attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;attr->usage = AUDIO_USAGE_MEDIA;

2.prepareAsync的调用流程

frameworks\av\media\libmediaplayerservice\MediaPlayerService.cpp

status_t MediaPlayerService::Client::prepareAsync()
{ALOGE("[%d] prepareAsync", mConnId);sp<MediaPlayerBase> p = getPlayer();if (p == 0) return UNKNOWN_ERROR;status_t ret = p->prepareAsync();
#if CALLBACK_ANTAGONIZERALOGD("start Antagonizer");if (ret == NO_ERROR) mAntagonizer->start();
#endifreturn ret;
}

frameworks\av\media\libmediaplayerservice\nuplayer\NuPlayerDriver.cpp

status_t NuPlayerDriver::prepareAsync() {ALOGV("prepareAsync(%p)", this);Mutex::Autolock autoLock(mLock);switch (mState) {case STATE_UNPREPARED:mState = STATE_PREPARING;mIsAsyncPrepare = true;mPlayer->prepareAsync();return OK;case STATE_STOPPED:// this is really just paused. handle as seek to startmAtEOS = false;mState = STATE_STOPPED_AND_PREPARING;mIsAsyncPrepare = true;mPlayer->seekToAsync(0, true /* needNotify */);return OK;default:return INVALID_OPERATION;};
}

frameworks\av\media\libmediaplayerservice\nuplayer\NuPlayer.cpp

void NuPlayer::prepareAsync() {(new AMessage(kWhatPrepare, this))->post();
}

这里使用了Native的Handle机制，这个机制原理上和JAVA端的是一致的。
先看处理这个handle的线程是在什么地方创建的，如下

frameworks\av\media\libmediaplayerservice\nuplayer\NuPlayerDriver.cpp

NuPlayerDriver::NuPlayerDriver(pid_t pid): mState(STATE_IDLE),mIsAsyncPrepare(false),mAsyncResult(UNKNOWN_ERROR),mSetSurfaceInProgress(false),mDurationUs(-1),mPositionUs(-1),mSeekInProgress(false),mLooper(new ALooper),mPlayerFlags(0),mAtEOS(false),mLooping(false),mAutoLoop(false) {ALOGV("NuPlayerDriver(%p)", this);mLooper->setName("NuPlayerDriver Looper");//开启线程mLooper->start(false, /* runOnCallingThread */true,  /* canCallJava */PRIORITY_AUDIO);mPlayer = AVNuFactory::get()->createNuPlayer(pid);mLooper->registerHandler(mPlayer);mPlayer->setDriver(this);
}

如上，Looper会创建一个名为"NuPlayerDriver Looper"的线程，随后调用mLooper->start开启这个线程，之后循环等待是否有事件需要处理；

mLooper->registerHandler(mPlayer);

上面是为Looper设置handle(mPlayer继承自AHandler)，之后AMessage将消息发送到Looper线程，随后线程回调AHandler的onMessageReceived方法去处理。这里需要注意的是onMessageReceived有可能会被AHandler的派生类重载。

AHandler的理论讲完了，回到NuPlayer::prepareAsync(),这里面通过AMessage将消息kWhatPrepare发送到了NuPlayer的onMessageReceived方法：

void NuPlayer::onMessageReceived(const sp<AMessage> &msg) {...case kWhatPrepare:{mSource->prepareAsync();break;}...
}

这里的mSource在上一步kWhatSetDataSource消息的处理中已经完成赋值了
这里的mSource指向的是GenericSource对象，因此prepareAsync会走向

frameworks\av\media\libmediaplayerservice\nuplayer\GenericSource.cpp

void NuPlayer::GenericSource::prepareAsync() {if (mLooper == NULL) {mLooper = new ALooper;mLooper->setName("generic");mLooper->start();mLooper->registerHandler(this);}sp<AMessage> msg = new AMessage(kWhatPrepareAsync, this);msg->post();
}

如上GenericSource内部又开启了一个线程(“generic”),这个线程处理来自GenericSource的消息，因此，这条消息会继续发往GenericSource的onMessageReceived

void NuPlayer::GenericSource::onMessageReceived(const sp<AMessage> &msg) {switch (msg->what()) {case kWhatPrepareAsync:{onPrepareAsync();break;}...
}
...
void NuPlayer::GenericSource::onPrepareAsync() {...创建DataSourcemDataSource = new FileSource(mFd, mOffset, mLength);...//进行多媒体文件的格式探测和解析status_t err = initFromDataSource();// 上报流状态notifyFlagsChanged((mIsSecure ? FLAG_SECURE : 0)| (mDecryptHandle != NULL ? FLAG_PROTECTED : 0)| FLAG_CAN_PAUSE| FLAG_CAN_SEEK_BACKWARD| FLAG_CAN_SEEK_FORWARD| FLAG_CAN_SEEK);...//上报调用完成finishPrepareAsync();...
}

我们重点关注initFromDataSource中的多媒体文件探测和解析

status_t NuPlayer::GenericSource::initFromDataSource() {...//创建多媒体探测器，这里会通过binder调度到MediaExtractor获取对应的解析器，例如MP3会使用MP3Extractorextractor = MediaExtractor::Create(mDataSource,mimeType.isEmpty() ? NULL : mimeType.string(),mIsStreaming ? 0 : AVNuUtils::get()->getFlags());//获取多媒体文件的元数据           mFileMeta = extractor->getMetaData();   //获取多媒体文件总共有多少个tracksize_t numtracks = extractor->countTracks();       for (size_t i = 0; i < numtracks; ++i) {//获取每一个tracksp<IMediaSource> track = extractor->getTrack(i);//获取当前track的meta数据sp<MetaData> meta = extractor->getTrackMetaData(i);const char *mime;//从当前track的meta信息中得到，多媒体是audio还是videoCHECK(meta->findCString(kKeyMIMEType, &mime));if (!strncasecmp(mime, "audio/", 6)) {if (mAudioTrack.mSource == NULL) {mAudioTrack.mIndex = i;mAudioTrack.mSource = track;mAudioTrack.mPackets =new AnotherPacketSource(mAudioTrack.mSource->getFormat());if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_VORBIS)) {mAudioIsVorbis = true;} else {mAudioIsVorbis = false;}if (AVNuUtils::get()->isByteStreamModeEnabled(meta)) {mIsByteMode = true;}}} else if (!strncasecmp(mime, "video/", 6)) {....}}//获取时长if (meta->findInt64(kKeyDuration, &durationUs)) {if (durationUs > mDurationUs) {mDurationUs = durationUs;}}    ...

一般对于音频的文件而言，track只有一个，如下：

size_t MP3Extractor::countTracks() {return mInitCheck != OK ? 0 : 1;
}

参考文章：
NuPlayer播放框架之GenericSource源码分析

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