本文将基于Android N源码对NuPlayer做一个详解。NuPlayer是Android中本地和流媒体播放所用的播放器。

1、AHandler机制

首先介绍NuPlayer中无处不在的AHandler机制
frameworks/av/include/media/stagefright/foundation/
frameworks/av/media/libstagefright/foundation/
AHandler是Android native层实现的一个异步消息机制，在这个机制中所有的处理都是异步的，将变量封装到一个消息AMessage结构体中，然后放到队列中去，后台专门有一个线程会从这个队列中取出消息然后执行，执行函数就是onMessageReceived。

Ahandler机制包括以下几个类

• AMessage

消息类，用于构造消息，通过post方法投递出去给ALooper

status_t AMessage::post(int64_t delayUs) {
    sp<ALooper> looper = mLooper.promote();
    if (looper == NULL) {
        ALOGW("failed to post message as target looper for handler %d is gone.", mTarget);
        return -ENOENT;
    }

    looper->post(this, delayUs);
    return OK;
}

void AMessage::deliver() {
    sp<AHandler> handler = mHandler.promote();
    if (handler == NULL) {
        ALOGW("failed to deliver message as target handler %d is gone.", mTarget);
        return;
    }

    handler->deliverMessage(this); //see AHandler@deliverMessage，前面通过looper post最后就是调用这里的deliever送到handler手里
}

• AHandler
  消息处理类，一般当做父类，继承该类的子类需要实现onMessageReceived方法

void AHandler::deliverMessage(const sp<AMessage> &msg) {
    onMessageReceived(msg);
    mMessageCounter++;
….
}

• ALooper
  与Ahander一一对应，负责存储消息并分发Ahandler的消息，与AMessage一对多关系

// posts a message on this looper with the given timeout
void ALooper::post(const sp<AMessage> &msg, int64_t delayUs) {
    Mutex::Autolock autoLock(mLock);

    int64_t whenUs;
    if (delayUs > 0) {
        whenUs = GetNowUs() + delayUs;
    } else {
        whenUs = GetNowUs();
    }

    List<Event>::iterator it = mEventQueue.begin();
    while (it != mEventQueue.end() && (*it).mWhenUs <= whenUs) {
        ++it;
    }

    Event event;
    event.mWhenUs = whenUs;
    event.mMessage = msg;

    if (it == mEventQueue.begin()) {
        mQueueChangedCondition.signal();
    }

    mEventQueue.insert(it, event);
}
----------------------------------------------------------
status_t ALooper::start(
        bool runOnCallingThread, bool canCallJava, int32_t priority) {
    if (runOnCallingThread) {
        {
            Mutex::Autolock autoLock(mLock);

            if (mThread != NULL || mRunningLocally) {
                return INVALID_OPERATION;
            }

            mRunningLocally = true;
        }

        do {
        } while (loop());

        return OK;
    }

    Mutex::Autolock autoLock(mLock);

    if (mThread != NULL || mRunningLocally) {
        return INVALID_OPERATION;
    }

    mThread = new LooperThread(this, canCallJava);

    status_t err = mThread->run(
            mName.empty() ? "ALooper" : mName.c_str(), priority);
    if (err != OK) {
        mThread.clear();
    }

    return err;
}
bool ALooper::loop() {
    Event event;

    {
        Mutex::Autolock autoLock(mLock);
        if (mThread == NULL && !mRunningLocally) {
            return false;
        }
        if (mEventQueue.empty()) {
            mQueueChangedCondition.wait(mLock);
            return true;
        }
        int64_t whenUs = (*mEventQueue.begin()).mWhenUs;
        int64_t nowUs = GetNowUs();

        if (whenUs > nowUs) {
            int64_t delayUs = whenUs - nowUs;
            mQueueChangedCondition.waitRelative(mLock, delayUs * 1000ll);

            return true;
        }

        event = *mEventQueue.begin();
        mEventQueue.erase(mEventQueue.begin());
    }

    event.mMessage->deliver();　//see AHandler.deliverMessage
…..
    return true;
}

• LooperThread
  此线程调用ALooper的loop方法来分发消息

 virtual status_t readyToRun() {
        mThreadId = androidGetThreadId();

        return Thread::readyToRun();
    }

    virtual bool threadLoop() {
        return mLooper->loop();
    }

• ALooperRoaster
  与Handler是一对多的关系， 管理Looper和Handler一一对应关系，负责释放stale handler

ALooper::handler_id ALooperRoster::registerHandler(
        const sp<ALooper> looper, const sp<AHandler> &handler) {
    Mutex::Autolock autoLock(mLock);

    if (handler->id() != 0) {
        CHECK(!"A handler must only be registered once.");
        return INVALID_OPERATION;
    }

    HandlerInfo info;
    info.mLooper = looper;
    info.mHandler = handler;
    ALooper::handler_id handlerID = mNextHandlerID++;//一对一
    mHandlers.add(handlerID, info);//一对多

    handler->setID(handlerID, looper);

    return handlerID;
}

void ALooperRoster::unregisterHandler(ALooper::handler_id handlerID) {
    Mutex::Autolock autoLock(mLock);

    ssize_t index = mHandlers.indexOfKey(handlerID);

    if (index < 0) {
        return;
    }

    const HandlerInfo &info = mHandlers.valueAt(index);

    sp<AHandler> handler = info.mHandler.promote();

    if (handler != NULL) {
        handler->setID(0, NULL);
    }

    mHandlers.removeItemsAt(index);
}

void ALooperRoster::unregisterStaleHandlers() {

    Vector<sp<ALooper> > activeLoopers;
    {
        Mutex::Autolock autoLock(mLock);

        for (size_t i = mHandlers.size(); i > 0;) {
            i--;
            const HandlerInfo &info = mHandlers.valueAt(i);

            sp<ALooper> looper = info.mLooper.promote();
            if (looper == NULL) {
                ALOGV("Unregistering stale handler %d", mHandlers.keyAt(i));
                mHandlers.removeItemsAt(i);
            } else {
                // At this point ‘looper‘ might be the only sp<> keeping
                // the object alive. To prevent it from going out of scope
                // and having ~ALooper call this method again recursively
                // and then deadlocking because of the Autolock above, add
                // it to a Vector which will go out of scope after the lock
                // has been released.
                activeLoopers.add(looper);
            }
        }
    }
}

• 异步消息机制的创建

sp<ALooper> mLooper = new ALooper; //创建一个Alooper实例
sp<AHandlerReflector> mHandler = new AHandlerReflector //创建一个Ahandler实例
mLooper->setName(“xxxxx”); //设置looper名字
mLooper->start(false, true, PRIORITY_XXX); //根据参数创建并启动 looper thread
mLooper->regiserHandler(mHandler); //register handler 会调用AHandler的setID方法将looper设置到Handler里去

• Post消息

sp<AMessage> msg = new AMessage(kWhatSayGoodbye, mHandler); //在AMessage的构造方法里获取Ahandler对应的Looper并保存
msg->post(); // 调用looper的post方法

Message Post的调用过程
Message::post
↓
ALooper::post
mEventQueue.insert
mQueueChangedCondition.signal() //如果之前没有event，通知looper thread
↓
ALooper::loop()
if (mEventQueue.empty()) { //如果消息队列为空，则等待
mQueueChangedCondition.wait(mLock);
return true;
}
event = *mEventQueue.begin();
event.mMessage->deliver();
↓
AHandler::deliverMessage
↓
AHandlerReflector:: onMessageReceived
↓
具体的实现

NuPlayer

下面就进入我们的正题，NuPlayer
frameworks/av/media/libmediaplayerservice/nuplayer/

• NuPlayerDriver
  NuPlayerDriver是对NuPlayer的封装，继承MediaPlayerInterface接口。通过NuPlayer来实现播放的功能。看这部分代码的方法就是先看NuPlayerDriver里面干了啥，转头就去找NuPlayer里面的实现，一般都要再去NuPlayer的onMessageReceive中看消息的响应，最后回到NuPlayerDriver的各种notify中看流程的周转，下面附上一张播放器状态机流转图
  

NuPlayerDriver::NuPlayerDriver(pid_t pid)
    : mState(STATE_IDLE),  //对应播放器状态机的初始化状态
      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);
    //和前面所述的异步消息创建机制相符
　mLooper->setName("NuPlayerDriver Looper");

    mLooper->start(
            false, /* runOnCallingThread */
            true,  /* canCallJava */
            PRIORITY_AUDIO);
　//mPlayer即NuPlayer，继承于AHandler
    mPlayer = AVNuFactory::get()->createNuPlayer(pid);
    mLooper->registerHandler(mPlayer);

    mPlayer->setDriver(this);
}

NuPlayerDriver::~NuPlayerDriver() {
    ALOGV("~NuPlayerDriver(%p)", this);
    mLooper->stop();    //整个NuPlayerDriver就是一个大ALooper
}

• AVNuFactory
  负责关键组件的create，通过它能看到：
  1.每一个NuPlayer对应一个进程
  2.数据流从Source-Decoder-Renderer，中间由AMessages驱动

sp<NuPlayer> AVNuFactory::createNuPlayer(pid_t pid) {
    return new NuPlayer(pid);
}

sp<NuPlayer::DecoderBase> AVNuFactory::createPassThruDecoder(
            const sp<AMessage> &notify,
            const sp<NuPlayer::Source> &source,
            const sp<NuPlayer::Renderer> &renderer) {
    return new NuPlayer::DecoderPassThrough(notify, source, renderer);
}

sp<NuPlayer::DecoderBase> AVNuFactory::createDecoder(
            const sp<AMessage> &notify,
            const sp<NuPlayer::Source> &source,
            pid_t pid,
            const sp<NuPlayer::Renderer> &renderer) {
    return new NuPlayer::Decoder(notify, source, pid, renderer);
}

sp<NuPlayer::Renderer> AVNuFactory::createRenderer(
            const sp<MediaPlayerBase::AudioSink> &sink,
            const sp<AMessage> &notify,
            uint32_t flags) {
    return new NuPlayer::Renderer(sink, notify, flags);
}

下面分别分析Source, Decoder, Renderer

Source

以setDataSource为切入点

status_t NuPlayerDriver::setDataSource(const sp<IStreamSource> &source) {
    ALOGV("setDataSource(%p) stream source", this);
    Mutex::Autolock autoLock(mLock);

    if (mState != STATE_IDLE) {
        return INVALID_OPERATION;
    }

    mState = STATE_SET_DATASOURCE_PENDING;

    mPlayer->setDataSourceAsync(source);//因为driver只是NuPlayer的封装，所以还是要去调用NuPlayer完成实际动作

    while (mState == STATE_SET_DATASOURCE_PENDING) {
        mCondition.wait(mLock);
    }

    return mAsyncResult;
}
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void NuPlayer::setDataSourceAsync(const sp<IStreamSource> &source) {
    sp<AMessage> msg = new AMessage(kWhatSetDataSource, this);

    sp<AMessage> notify = new AMessage(kWhatSourceNotify, this);

    msg->setObject("source", new StreamingSource(notify, source));
    msg->post();　//到了NuPlayer中，也不是直接进行操作，而是先发个消息，验证前面所说的一切都由AMessage驱动
}
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void NuPlayer::onMessageReceived(const sp<AMessage> &msg) {
    switch (msg->what()) {
        case kWhatSetDataSource://实际的处理在这里
        {
            ALOGV("kWhatSetDataSource");

            CHECK(mSource == NULL);

            status_t err = OK;
            sp<RefBase> obj;
            CHECK(msg->findObject("source", &obj));
            if (obj != NULL) {
                Mutex::Autolock autoLock(mSourceLock);
                mSource = static_cast<Source *>(obj.get());//赋值给mSource
            } else {
                err = UNKNOWN_ERROR;
            }

            CHECK(mDriver != NULL);
            sp<NuPlayerDriver> driver = mDriver.promote();
            if (driver != NULL) {
                driver->notifySetDataSourceCompleted(err);//通知driver设置完毕
            }
            break;
        }......
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void NuPlayerDriver::notifySetDataSourceCompleted(status_t err) {
    Mutex::Autolock autoLock(mLock);

    CHECK_EQ(mState, STATE_SET_DATASOURCE_PENDING);

    mAsyncResult = err;
    mState = (err == OK) ? STATE_UNPREPARED : STATE_IDLE;//回到driver中，流转播放器状态进入下一阶段
    mCondition.broadcast();
}

下面就来看看具体有哪些source，它们都继承自NuPlayer:Source（NuPlayerSource.h & NuPlayerSource.cpp）
1.HTTP-进一步判断是以下的哪一种：HTTPLiveSource,RTSPSource,GenericSource
2.File-GenericSource
3.StreamSource-StreamingSource
4.DataSource-GenericSource

• GenericSource

nuplayer/GenericSource.h & GenericSource.cpp

几个水位
static int64_t kLowWaterMarkUs = 2000000ll;  // 2secs
static int64_t kHighWaterMarkUs = 5000000ll;  // 5secs
static int64_t kHighWaterMarkRebufferUs = 15000000ll;  // 15secs,这一个是新增加的水位
static const ssize_t kLowWaterMarkBytes = 40000;
static const ssize_t kHighWaterMarkBytes = 200000;

status_t NuPlayer::GenericSource::initFromDataSource() {
init extractor;get track info and metadata
}

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();
}

status_t NuPlayer::GenericSource::feedMoreTSData() {
    return OK;
}

• LiveSession

libstagefright/httplive/LiveSession.h & cpp

// static
// Bandwidth Switch Mark Defaults
const int64_t LiveSession::kUpSwitchMarkUs = 15000000ll;
const int64_t LiveSession::kDownSwitchMarkUs = 20000000ll;
const int64_t LiveSession::kUpSwitchMarginUs = 5000000ll;
const int64_t LiveSession::kResumeThresholdUs = 100000ll;

// Buffer Prepare/Ready/Underflow Marks
const int64_t LiveSession::kReadyMarkUs = 5000000ll;
const int64_t LiveSession::kPrepareMarkUs = 1500000ll;
const int64_t LiveSession::kUnderflowMarkUs = 1000000ll;

与Fetcher,Bandwidth Estimater(和ExoPlayer一样是滑动窗口平均),switching,Buffering相关的操作都在这里

• HTTPLiveSource

nuplayer目录下

enum Flags {
        // Don‘t log any URLs.不在log中记录URL
        kFlagIncognito = 1,
    };

NuPlayer::HTTPLiveSource::HTTPLiveSource(
    if (headers) {　//也搞了一个header机制
        mExtraHeaders = *headers;

        ssize_t index =
            mExtraHeaders.indexOfKey(String8("x-hide-urls-from-log"));

        if (index >= 0) {
            mFlags |= kFlagIncognito;

            mExtraHeaders.removeItemsAt(index);
        }
    }
}
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void NuPlayer::HTTPLiveSource::prepareAsync() {
    if (mLiveLooper == NULL) {
        mLiveLooper = new ALooper;//一如既往的ALooper
        mLiveLooper->setName("http live");
        mLiveLooper->start();

        mLiveLooper->registerHandler(this);
    }

    sp<AMessage> notify = new AMessage(kWhatSessionNotify, this);

    mLiveSession = new LiveSession(
            notify,
            (mFlags & kFlagIncognito) ? LiveSession::kFlagIncognito : 0,
            mHTTPService);

    mLiveLooper->registerHandler(mLiveSession);

    mLiveSession->connectAsync(//HTTPLiveSource包含LiveSession，很多实际的工作都由LiveSession完成
            mURL.c_str(), mExtraHeaders.isEmpty() ? NULL : &mExtraHeaders);
}

• ATSParser
  frameworks/av/media/libstagefright/mpeg2ts/ATSParser.cpp
  就是一个TS Parser，虽然也叫Axx，但是没有消息机制在里面

• StreamingSource
  nuplayer目录

void NuPlayer::StreamingSource::prepareAsync() {
    if (mLooper == NULL) {
        mLooper = new ALooper;
        mLooper->setName("streaming");
        mLooper->start();//何其相似

        mLooper->registerHandler(this);
    }

    notifyVideoSizeChanged();
    notifyFlagsChanged(0);
    notifyPrepared();
}
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StreamingSource中的数据由onReadBuffer驱动，最后的EOS,Discontiunity等都交给ATSParser去处理，ATSParser又最终交给AnotherPacketSource去做真正的处理．实际上，这里提到的三个Source最后都会用到AnotherPacketSource

void NuPlayer::StreamingSource::onReadBuffer() {
    for (int32_t i = 0; i < kNumListenerQueuePackets; ++i) {
        char buffer[188];
        sp<AMessage> extra;
        ssize_t n = mStreamListener->read(buffer, sizeof(buffer), &extra);//实际用NuPlayerStreamListener完成工作

        if (n == 0) {
            ALOGI("input data EOS reached.");
            mTSParser->signalEOS(ERROR_END_OF_STREAM);//EOS了
            setError(ERROR_END_OF_STREAM);
            break;
        } else if (n == INFO_DISCONTINUITY) {
            int32_t type = ATSParser::DISCONTINUITY_TIME;

            int32_t mask;
            if (extra != NULL
                    && extra->findInt32(
                        IStreamListener::kKeyDiscontinuityMask, &mask)) {
                if (mask == 0) {
                    ALOGE("Client specified an illegal discontinuity type.");
                    setError(ERROR_UNSUPPORTED);
                    break;
                }

                type = mask;
            }
 mTSParser->signalDiscontinuity(
                    (ATSParser::DiscontinuityType)type, extra);
        } else if (n < 0) {
            break;
        } else {
            if (buffer[0] == 0x00) {
                // XXX legacy

                if (extra == NULL) {
                    extra = new AMessage;
                }

                uint8_t type = buffer[1];

                if (type & 2) {
                    int64_t mediaTimeUs;
                    memcpy(&mediaTimeUs, &buffer[2], sizeof(mediaTimeUs));

                    extra->setInt64(IStreamListener::kKeyMediaTimeUs, mediaTimeUs);
                }

                mTSParser->signalDiscontinuity(
                        ((type & 1) == 0)
                            ? ATSParser::DISCONTINUITY_TIME
                            : ATSParser::DISCONTINUITY_FORMATCHANGE,
                        extra);
            } else {
                status_t err = mTSParser->feedTSPacket(buffer, sizeof(buffer));

                if (err != OK) {
                    ALOGE("TS Parser returned error %d", err);

                    mTSParser->signalEOS(err);
                    setError(err);
                    break;
                }
            }
        }
    }
}

• AnotherPacketSource

frameworks/av/media/libstagefright/mpeg2ts
可以类比ExoPlayer中的chunk source，同时负责buffer管理，EOS\Discontinuity的处理等等．前面三个Source最后都会落到AnotherPacketSource

bool AnotherPacketSource::hasBufferAvailable(status_t *finalResult) {
    Mutex::Autolock autoLock(mLock);
    *finalResult = OK;
    if (!mEnabled) {
        return false;
    }
    if (!mBuffers.empty()) {//一个ABuffer List，其实就是一个环形缓冲
        return true;
    }

    *finalResult = mEOSResult;
    return false;
}
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void AnotherPacketSource::queueDiscontinuity(
        ATSParser::DiscontinuityType type,
        const sp<AMessage> &extra,
        bool discard) {
    Mutex::Autolock autoLock(mLock);

    if (discard) {
        // Leave only discontinuities in the queue.
…...
    }

    mEOSResult = OK;
    mLastQueuedTimeUs = 0;
    mLatestEnqueuedMeta = NULL;

    if (type == ATSParser::DISCONTINUITY_NONE) {
        return;
    }

    mDiscontinuitySegments.push_back(DiscontinuitySegment());

    sp<ABuffer> buffer = new ABuffer(0);
    buffer->meta()->setInt32("discontinuity", static_cast<int32_t>(type));
    buffer->meta()->setMessage("extra", extra);

    mBuffers.push_back(buffer);　//将记录了discontinuity的ABuffer推入缓冲区中，这样各个Source在从缓冲区读数据的时候就能正确处理discontinuity了
    mCondition.signal();
}

Decoder

Decoder是如何被初始化的

从NuPlayer::OnStart方法看起
void NuPlayer::onStart(int64_t startPositionUs) {
    if (!mSourceStarted) {
        mSourceStarted = true;
        mSource->start();
    }
    if (startPositionUs > 0) {
        performSeek(startPositionUs);
        if (mSource->getFormat(false /* audio */) == NULL) {
            return;
        }
    }
．．．
    sp<AMessage> notify = new AMessage(kWhatRendererNotify, this);
    ++mRendererGeneration;
    notify->setInt32("generation", mRendererGeneration);
    //在这里用AVNuFactory初始化Renderer和它对应的Looper
    mRenderer = AVNuFactory::get()->createRenderer(mAudioSink, notify, flags);
    mRendererLooper = new ALooper;
    mRendererLooper->setName("NuPlayerRenderer");
    mRendererLooper->start(false, false, ANDROID_PRIORITY_AUDIO);
    mRendererLooper->registerHandler(mRenderer);
　//设置Renderer的播放参数
    status_t err = mRenderer->setPlaybackSettings(mPlaybackSettings);
    ．．．
　//给Decoder设置Renderer，两者之间的关系建立起来了
    if (mVideoDecoder != NULL) {
        mVideoDecoder->setRenderer(mRenderer);
    }
    if (mAudioDecoder != NULL) {
        mAudioDecoder->setRenderer(mRenderer);
    }
　//抛出这一消息
    postScanSources();
}
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case kWhatScanSources:
        {
            int32_t generation;
            CHECK(msg->findInt32("generation", &generation));
            if (generation != mScanSourcesGeneration) {
                // Drop obsolete msg.
                break;
            }

            mScanSourcesPending = false;

            ALOGV("scanning sources haveAudio=%d, haveVideo=%d",
                 mAudioDecoder != NULL, mVideoDecoder != NULL);

            bool mHadAnySourcesBefore =
                (mAudioDecoder != NULL) || (mVideoDecoder != NULL);
            bool rescan = false;

            // initialize video before audio because successful initialization of
            // video may change deep buffer mode of audio.
　　　//在这里初始化decoder
            if (mSurface != NULL) {
                if (instantiateDecoder(false, &mVideoDecoder) == -EWOULDBLOCK) {
                    rescan = true;
                }
            }

            // Don‘t try to re-open audio sink if there‘s an existing decoder.
            if (mAudioSink != NULL && mAudioDecoder == NULL) {
                if (instantiateDecoder(true, &mAudioDecoder) == -EWOULDBLOCK) {
                    rescan = true;
                }
            }

            if (!mHadAnySourcesBefore
                    && (mAudioDecoder != NULL || mVideoDecoder != NULL)) {
                // This is the first time we‘ve found anything playable.

                if (mSourceFlags & Source::FLAG_DYNAMIC_DURATION) {
                    schedulePollDuration();
                }
            }

            status_t err;
            if ((err = mSource->feedMoreTSData()) != OK) {
                if (mAudioDecoder == NULL && mVideoDecoder == NULL) {
                    // We‘re not currently decoding anything (no audio or
                    // video tracks found) and we just ran out of input data.

                    if (err == ERROR_END_OF_STREAM) {
                        notifyListener(MEDIA_PLAYBACK_COMPLETE, 0, 0);
                    } else {
                        notifyListener(MEDIA_ERROR, MEDIA_ERROR_UNKNOWN, err);
                    }
                }
                break;
            }
            //postScanSources和ExoPlayer中的doSomeWork一样是一个不断循环运转的东西
            if (rescan) {
                msg->post(100000ll);
                mScanSourcesPending = true;
            }
            break;
        }
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在NuPlayer的instantiateDecoder中完成Decoder的初始化
status_t NuPlayer::instantiateDecoder(
        bool audio, sp<DecoderBase> *decoder, bool checkAudioModeChange) {
   ．．．
　
    if (!audio) {
        AString mime;
        CHECK(format->findString("mime", &mime));

        sp<AMessage> ccNotify = new AMessage(kWhatClosedCaptionNotify, this);
        if (mCCDecoder == NULL) {
            mCCDecoder = new CCDecoder(ccNotify);　//new字幕解码器
        }

        if (mSourceFlags & Source::FLAG_SECURE) {
            format->setInt32("secure", true);
        }

        if (mSourceFlags & Source::FLAG_PROTECTED) {
            format->setInt32("protected", true);
        }

        float rate = getFrameRate();
        if (rate > 0) {
            format->setFloat("operating-rate", rate * mPlaybackSettings.mSpeed);
        }
    }

    if (audio) {
        sp<AMessage> notify = new AMessage(kWhatAudioNotify, this);
        ++mAudioDecoderGeneration;
        notify->setInt32("generation", mAudioDecoderGeneration);

        if (checkAudioModeChange) {
            determineAudioModeChange(format);
        }
        if (mOffloadAudio)
            mSource->setOffloadAudio(true /* offload */);

        if (mOffloadAudio) {
            const bool hasVideo = (mSource->getFormat(false /*audio */) != NULL);
            format->setInt32("has-video", hasVideo);
            *decoder = AVNuFactory::get()->createPassThruDecoder(notify, mSource, mRenderer);//利用AVNuFactory的方法创建pass through的音频解码器
        } else {
            AVNuUtils::get()->setCodecOutputFormat(format);
            mSource->setOffloadAudio(false /* offload */);
            *decoder = AVNuFactory::get()->createDecoder(notify, mSource, mPID, mRenderer);//创建普通的音频解码器
        }
    } else {
        sp<AMessage> notify = new AMessage(kWhatVideoNotify, this);
        ++mVideoDecoderGeneration;
        notify->setInt32("generation", mVideoDecoderGeneration);

        *decoder = new Decoder(
                notify, mSource, mPID, mRenderer, mSurface, mCCDecoder);
　　　//new视频解码器，这里还会把字幕解码器作为一个参数传进来
        // enable FRC if high-quality AV sync is requested, even if not
        // directly queuing to display, as this will even improve textureview
        // playback.
        {
            char value[PROPERTY_VALUE_MAX];
            if (property_get("persist.sys.media.avsync", value, NULL) &&
                    (!strcmp("1", value) || !strcasecmp("true", value))) {
                format->setInt32("auto-frc", 1);
            }
        }
    }
    (*decoder)->init();//解码器初始化
    (*decoder)->configure(format);//解码器配置

    // allocate buffers to decrypt widevine source buffers
    if (!audio && (mSourceFlags & Source::FLAG_SECURE)) {
        Vector<sp<ABuffer> > inputBufs;
        CHECK_EQ((*decoder)->getInputBuffers(&inputBufs), (status_t)OK);

        Vector<MediaBuffer *> mediaBufs;
        for (size_t i = 0; i < inputBufs.size(); i++) {
            const sp<ABuffer> &buffer = inputBufs[i];
            MediaBuffer *mbuf = new MediaBuffer(buffer->data(), buffer->size());
            mediaBufs.push(mbuf);
        }

        status_t err = mSource->setBuffers(audio, mediaBufs);
        if (err != OK) {
            for (size_t i = 0; i < mediaBufs.size(); ++i) {
                mediaBufs[i]->release();
            }
            mediaBufs.clear();
            ALOGE("Secure source didn‘t support secure mediaBufs.");
            return err;
        }
    }
．．．
    return OK;
}
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void NuPlayer::Decoder::doFlush(bool notifyComplete) {
    if (mCCDecoder != NULL) {
        mCCDecoder->flush();//先flush字幕Decoder
    }

    if (mRenderer != NULL) {
        mRenderer->flush(mIsAudio, notifyComplete);
        mRenderer->signalTimeDiscontinuity();//再flush Renderer
    }

    status_t err = OK;
    if (mCodec != NULL) {
        err = mCodec->flush();//最后flush Decoder
        mCSDsToSubmit = mCSDsForCurrentFormat; // copy operator
        ++mBufferGeneration;
    }
．．．
    releaseAndResetMediaBuffers();//清空buffer
    mPaused = true;
}

• DecoderBase
  是NuPlayer::Decoder的基类，内部也维护了一个Looper，各种工作也依然是异步消息驱动完成的，只不过各种onMessage的响应方法都是虚函数，需要由子类来做具体的实现．也能看到利用setRenderer方法和Renderer结合到一起的方法

NuPlayer::DecoderBase::DecoderBase(const sp<AMessage> &notify)
    :  mNotify(notify),
       mBufferGeneration(0),
       mPaused(false),
       mStats(new AMessage),
       mRequestInputBuffersPending(false) {
    // Every decoder has its own looper because MediaCodec operations
    // are blocking, but NuPlayer needs asynchronous operations.
    mDecoderLooper = new ALooper;
    mDecoderLooper->setName("NPDecoder");
    mDecoderLooper->start(false, false, ANDROID_PRIORITY_AUDIO);
}

void NuPlayer::DecoderBase::init() {
    mDecoderLooper->registerHandler(this);
}

• NuPlayer::Decoder

由相应的onMessage方法处理各种工作
先关注init和configure两个方法，init直接继承自DecoderBase，就是给Looper注册Handler
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void NuPlayer::Decoder::onConfigure(const sp<AMessage> &format) {
．．．
　mCodec = AVUtils::get()->createCustomComponentByName(mCodecLooper, mime.c_str(), false /* encoder */, format);
    if (mCodec == NULL) {
   //由mimeType创建Decoder
    mCodec = MediaCodec::CreateByType(
            mCodecLooper, mime.c_str(), false /* encoder */, NULL /* err */, mPid);
    }
．．．
//mCodec就是libstagefright中的MediaCodec，没什么可说的
err = mCodec->configure(
            format, mSurface, NULL /* crypto */, 0 /* flags */);
    if (err != OK) {
        ALOGE("Failed to configure %s decoder (err=%d)", mComponentName.c_str(), err);
        mCodec->release();
        mCodec.clear();
        handleError(err);
        return;
    }
    rememberCodecSpecificData(format);
  // the following should work in configured state读Format信息
    CHECK_EQ((status_t)OK, mCodec->getOutputFormat(&mOutputFormat));
    CHECK_EQ((status_t)OK, mCodec->getInputFormat(&mInputFormat));

    mStats->setString("mime", mime.c_str());
    mStats->setString("component-name", mComponentName.c_str());

    if (!mIsAudio) {
        int32_t width, height;
        if (mOutputFormat->findInt32("width", &width)
                && mOutputFormat->findInt32("height", &height)) {
            mStats->setInt32("width", width);
            mStats->setInt32("height", height);
        }
    }
．．．
//MediaCodec开始
err = mCodec->start();
    if (err != OK) {
        ALOGE("Failed to start %s decoder (err=%d)", mComponentName.c_str(), err);
        mCodec->release();
        mCodec.clear();
        handleError(err);
        return;
    }
//先把buffer都release置为null
    releaseAndResetMediaBuffers();
．．．
｝

前面提到NuPlayer::Decoder里面有一个MediaCodec，所以不用再研究具体怎么解码的，关注点在于从这个模块输出的东西是怎样的，以及是怎样输入这个东西的
先来看输出：
当MediaCodec有Available Output的时候，在onMessageReceived中有
case MediaCodec::CB_OUTPUT_AVAILABLE:
                {
                    int32_t index;
                    size_t offset;
                    size_t size;
                    int64_t timeUs;
                    int32_t flags;

                    CHECK(msg->findInt32("index", &index));
                    CHECK(msg->findSize("offset", &offset));
                    CHECK(msg->findSize("size", &size));
                    CHECK(msg->findInt64("timeUs", &timeUs));
                    CHECK(msg->findInt32("flags", &flags));

                    handleAnOutputBuffer(index, offset, size, timeUs, flags);
                    break;
                }
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bool NuPlayer::Decoder::handleAnOutputBuffer(
        size_t index,
        size_t offset,
        size_t size,
        int64_t timeUs,
        int32_t flags) {
//    CHECK_LT(bufferIx, mOutputBuffers.size());
    sp<ABuffer> buffer;
    mCodec->getOutputBuffer(index, &buffer);
．．．．
　//发送kWhatRenderBuffer消息
    sp<AMessage> reply = new AMessage(kWhatRenderBuffer, this);
    reply->setSize("buffer-ix", index);
    reply->setInt32("generation", mBufferGeneration);

    if (eos) {
        ALOGI("[%s] saw output EOS", mIsAudio ? "audio" : "video");
　　　　//EOS了
        buffer->meta()->setInt32("eos", true);
        reply->setInt32("eos", true);
    } else if (mSkipRenderingUntilMediaTimeUs >= 0) {
        if (timeUs < mSkipRenderingUntilMediaTimeUs) {
            ALOGV("[%s] dropping buffer at time %lld as requested.",
                     mComponentName.c_str(), (long long)timeUs);
　　　　//中间这一段不用render,skip掉
            reply->post();
            return true;
        }

        mSkipRenderingUntilMediaTimeUs = -1;
    } else if ((flags & MediaCodec::BUFFER_FLAG_DATACORRUPT) &&
            AVNuUtils::get()->dropCorruptFrame()) {
        ALOGV("[%s] dropping corrupt buffer at time %lld as requested.",
                     mComponentName.c_str(), (long long)timeUs);
　　//本段buffer坏到了，扔掉
        reply->post();
        return true;
    }

    mNumFramesTotal += !mIsAudio;

    // wait until 1st frame comes out to signal resume complete
    notifyResumeCompleteIfNecessary();

    if (mRenderer != NULL) {
        // send the buffer to renderer.把Buffer送到Renderer
        mRenderer->queueBuffer(mIsAudio, buffer, reply);
        if (eos && !isDiscontinuityPending()) {
            mRenderer->queueEOS(mIsAudio, ERROR_END_OF_STREAM);
        }
    }

    return true;
}
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case kWhatRenderBuffer:
        {
            if (!isStaleReply(msg)) {
                onRenderBuffer(msg);
            }
            break;
        }
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void NuPlayer::Decoder::onRenderBuffer(const sp<AMessage> &msg) {
    ．．．
    if (!mIsAudio) {
        int64_t timeUs;
        sp<ABuffer> buffer = mOutputBuffers[bufferIx];
        buffer->meta()->findInt64("timeUs", &timeUs);

        if (mCCDecoder != NULL && mCCDecoder->isSelected()) {
            mCCDecoder->display(timeUs);//字幕显示
        }
    }

    if (msg->findInt32("render", &render) && render) {
        int64_t timestampNs;
        CHECK(msg->findInt64("timestampNs", &timestampNs));

//由MediaCodec的renderOutputBufferAndRelease完成
        err = mCodec->renderOutputBufferAndRelease(bufferIx, timestampNs);
    } else {
        mNumOutputFramesDropped += !mIsAudio;
        err = mCodec->releaseOutputBuffer(bufferIx);
    }
    ．．．
}
再来看输入
当MediaCodec有Available Input的时候，在onMessageReceived中有
case MediaCodec::CB_INPUT_AVAILABLE:
                {
                    int32_t index;
                    CHECK(msg->findInt32("index", &index));

                    handleAnInputBuffer(index);
                    break;
                }
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bool NuPlayer::Decoder::handleAnInputBuffer(size_t index) {
   ．．．

    sp<ABuffer> buffer;
    mCodec->getInputBuffer(index, &buffer);
．．．
    if (index >= mInputBuffers.size()) {
        for (size_t i = mInputBuffers.size(); i <= index; ++i) {
            mInputBuffers.add();
            mMediaBuffers.add();
            mInputBufferIsDequeued.add();
            mMediaBuffers.editItemAt(i) = NULL;
            mInputBufferIsDequeued.editItemAt(i) = false;
        }
    }
    mInputBuffers.editItemAt(index) = buffer;

    //CHECK_LT(bufferIx, mInputBuffers.size());

    if (mMediaBuffers[index] != NULL) {
        mMediaBuffers[index]->release();
        mMediaBuffers.editItemAt(index) = NULL;
    }
    mInputBufferIsDequeued.editItemAt(index) = true;

    if (!mCSDsToSubmit.isEmpty()) {
        sp<AMessage> msg = new AMessage();
        msg->setSize("buffer-ix", index);

        sp<ABuffer> buffer = mCSDsToSubmit.itemAt(0);
        ALOGI("[%s] resubmitting CSD", mComponentName.c_str());
        msg->setBuffer("buffer", buffer);
        mCSDsToSubmit.removeAt(0);
        if (!onInputBufferFetched(msg)) {
            handleError(UNKNOWN_ERROR);
            return false;
        }
        return true;
    }

    while (!mPendingInputMessages.empty()) {
        sp<AMessage> msg = *mPendingInputMessages.begin();
        if (!onInputBufferFetched(msg)) {
            break;
        }
        mPendingInputMessages.erase(mPendingInputMessages.begin());
    }

    if (!mInputBufferIsDequeued.editItemAt(index)) {
        return true;
    }

    mDequeuedInputBuffers.push_back(index);

    onRequestInputBuffers();
    return true;
}
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bool NuPlayer::Decoder::onInputBufferFetched(const sp<AMessage> &msg) {
    ．．．
    sp<ABuffer> buffer;
    bool hasBuffer = msg->findBuffer("buffer", &buffer);

    // handle widevine classic source - that fills an arbitrary input buffer
    MediaBuffer *mediaBuffer = NULL;
    if (hasBuffer) {
　　　//TODO：更多信息，可以研究mediabuffer
        mediaBuffer = (MediaBuffer *)(buffer->getMediaBufferBase());
        if (mediaBuffer != NULL) {
            // likely filled another buffer than we requested: adjust buffer index
            size_t ix;
            for (ix = 0; ix < mInputBuffers.size(); ix++) {
                const sp<ABuffer> &buf = mInputBuffers[ix];
                if (buf->data() == mediaBuffer->data()) {
                    // all input buffers are dequeued on start, hence the check
                    if (!mInputBufferIsDequeued[ix]) {
                        ALOGV("[%s] received MediaBuffer for #%zu instead of #%zu",
                                mComponentName.c_str(), ix, bufferIx);
                        mediaBuffer->release();
                        return false;
                    }

                    // TRICKY: need buffer for the metadata, so instead, set
                    // codecBuffer to the same (though incorrect) buffer to
                    // avoid a memcpy into the codecBuffer
                    codecBuffer = buffer;
                    codecBuffer->setRange(
                            mediaBuffer->range_offset(),
                            mediaBuffer->range_length());
                    bufferIx = ix;
                    break;
                }
            }
            CHECK(ix < mInputBuffers.size());
        }
    }

    if (buffer == NULL /* includes !hasBuffer */) {
        int32_t streamErr = ERROR_END_OF_STREAM;
        CHECK(msg->findInt32("err", &streamErr) || !hasBuffer);

        CHECK(streamErr != OK);

        // attempt to queue EOS
        status_t err = mCodec->queueInputBuffer(
                bufferIx,
                0,
                0,
                0,
                MediaCodec::BUFFER_FLAG_EOS);
        if (err == OK) {
            mInputBufferIsDequeued.editItemAt(bufferIx) = false;
        } else if (streamErr == ERROR_END_OF_STREAM) {
            streamErr = err;
            // err will not be ERROR_END_OF_STREAM
        }

        if (streamErr != ERROR_END_OF_STREAM) {
            ALOGE("Stream error for %s (err=%d), EOS %s queued",
                    mComponentName.c_str(),
                    streamErr,
                    err == OK ? "successfully" : "unsuccessfully");
            handleError(streamErr);
        }
    } else {
        sp<AMessage> extra;
        if (buffer->meta()->findMessage("extra", &extra) && extra != NULL) {
            int64_t resumeAtMediaTimeUs;
            if (extra->findInt64(
                        "resume-at-mediaTimeUs", &resumeAtMediaTimeUs)) {
                ALOGI("[%s] suppressing rendering until %lld us",
                        mComponentName.c_str(), (long long)resumeAtMediaTimeUs);
                mSkipRenderingUntilMediaTimeUs = resumeAtMediaTimeUs;
            }
        }

        int64_t timeUs = 0;
        uint32_t flags = 0;
        CHECK(buffer->meta()->findInt64("timeUs", &timeUs));

        int32_t eos, csd;
        // we do not expect SYNCFRAME for decoder
        if (buffer->meta()->findInt32("eos", &eos) && eos) {
            flags |= MediaCodec::BUFFER_FLAG_EOS;
        } else if (buffer->meta()->findInt32("csd", &csd) && csd) {
            flags |= MediaCodec::BUFFER_FLAG_CODECCONFIG;
        }

        // copy into codec buffer
        if (buffer != codecBuffer) {
            if (buffer->size() > codecBuffer->capacity()) {
                handleError(ERROR_BUFFER_TOO_SMALL);
                mDequeuedInputBuffers.push_back(bufferIx);
                return false;
            }
            codecBuffer->setRange(0, buffer->size());
            memcpy(codecBuffer->data(), buffer->data(), buffer->size());
        }

        status_t err = mCodec->queueInputBuffer(
                        bufferIx,
                        codecBuffer->offset(),
                        codecBuffer->size(),
                        timeUs,
                        flags);
        if (err != OK) {
            if (mediaBuffer != NULL) {
                mediaBuffer->release();
            }
            ALOGE("Failed to queue input buffer for %s (err=%d)",
                    mComponentName.c_str(), err);
            handleError(err);
        } else {
            mInputBufferIsDequeued.editItemAt(bufferIx) = false;
            if (mediaBuffer != NULL) {
                CHECK(mMediaBuffers[bufferIx] == NULL);
                mMediaBuffers.editItemAt(bufferIx) = mediaBuffer;
            }
        }
    }
    return true;
}不管做什么，最后都是MediaCodec.queueInputBuffer完成了实际工作
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void NuPlayer::DecoderBase::onRequestInputBuffers() {
    if (mRequestInputBuffersPending) {
        return;
    }

    // doRequestBuffers() return true if we should request more data
    if (doRequestBuffers()) {
        mRequestInputBuffersPending = true;
　　　//注意这里，会自己循环调用，不停地request
        sp<AMessage> msg = new AMessage(kWhatRequestInputBuffers, this);
        msg->post(10 * 1000ll);
    }
}
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 case kWhatRequestInputBuffers:
        {
            mRequestInputBuffersPending = false;
            onRequestInputBuffers();
            break;
        }
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/*
 * returns true if we should request more data
 */
bool NuPlayer::Decoder::doRequestBuffers() {
    // mRenderer is only NULL if we have a legacy widevine source that
    // is not yet ready. In this case we must not fetch input.
    if (isDiscontinuityPending() || mRenderer == NULL) {
        return false;
    }
    status_t err = OK;
    while (err == OK && !mDequeuedInputBuffers.empty()) {
        size_t bufferIx = *mDequeuedInputBuffers.begin();
        sp<AMessage> msg = new AMessage();
        msg->setSize("buffer-ix", bufferIx);
        err = fetchInputData(msg);
        if (err != OK && err != ERROR_END_OF_STREAM) {
            // if EOS, need to queue EOS buffer
            break;
        }
        mDequeuedInputBuffers.erase(mDequeuedInputBuffers.begin());

        if (!mPendingInputMessages.empty()
                || !onInputBufferFetched(msg)) {　　//前面分析过这个方法了
            mPendingInputMessages.push_back(msg);
        }
    }

    return err == -EWOULDBLOCK
            && mSource->feedMoreTSData() == OK;
}
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status_t NuPlayer::Decoder::fetchInputData(sp<AMessage> &reply) {
    sp<ABuffer> accessUnit;
    bool dropAccessUnit;
    do {
        //在这里调用source的方法，从而建立起了联系
        status_t err = mSource->dequeueAccessUnit(mIsAudio, &accessUnit);
．．．
｝while(...)
}
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至此，Decoder部分也分析完毕了

Renderer

nuplayer目录下
Renderer的初始化在NuPlayer::OnStart方法中完成

void NuPlayer::onStart(int64_t startPositionUs) {
   ．．．
    sp<AMessage> notify = new AMessage(kWhatRendererNotify, this);
    ++mRendererGeneration;
    notify->setInt32("generation", mRendererGeneration);
    mRenderer = AVNuFactory::get()->createRenderer(mAudioSink, notify, flags);
    mRendererLooper = new ALooper;
    mRendererLooper->setName("NuPlayerRenderer");
    mRendererLooper->start(false, false, ANDROID_PRIORITY_AUDIO);
    mRendererLooper->registerHandler(mRenderer);

    status_t err = mRenderer->setPlaybackSettings(mPlaybackSettings);
…...
    float rate = getFrameRate();
    if (rate > 0) {
        mRenderer->setVideoFrameRate(rate);
    }

    if (mVideoDecoder != NULL) {
        mVideoDecoder->setRenderer(mRenderer);
    }
    if (mAudioDecoder != NULL) {
        mAudioDecoder->setRenderer(mRenderer);
    }

    postScanSources();
}

Renderer的数据输入在NuPlayer::Decoder::handleAnOutputBuffer中完成

bool NuPlayer::Decoder::handleAnOutputBuffer(
        size_t index,
        size_t offset,
        size_t size,
        int64_t timeUs,
        int32_t flags) {
．．．
if (mRenderer != NULL) {
        // send the buffer to renderer.把Buffer送到Renderer
        mRenderer->queueBuffer(mIsAudio, buffer, reply);
        if (eos && !isDiscontinuityPending()) {
            mRenderer->queueEOS(mIsAudio, ERROR_END_OF_STREAM);
        }
    }
．．．
}
libmediaplayerservice/nuplayer/NuplayerRenderer.cpp
mRenderer->queueBuffer最终会调用下面的方法
void NuPlayer::Renderer::onQueueBuffer(const sp<AMessage> &msg) {
    int32_t audio;
    CHECK(msg->findInt32("audio", &audio));

    if (dropBufferIfStale(audio, msg)) {
        return;
    }

    if (audio) {
        mHasAudio = true;
    } else {
        mHasVideo = true;
    }

    if (mHasVideo) {
        if (mVideoScheduler == NULL) {
            mVideoScheduler = new VideoFrameScheduler();//初始化VideoFrameSche，用于VSync
            mVideoScheduler->init();
        }
    }

    sp<ABuffer> buffer;
    CHECK(msg->findBuffer("buffer", &buffer));

    sp<AMessage> notifyConsumed;
    CHECK(msg->findMessage("notifyConsumed", &notifyConsumed));

    QueueEntry entry;//可以理解为buffer循环队列的抽象
    entry.mBuffer = buffer;
    entry.mNotifyConsumed = notifyConsumed;
    entry.mOffset = 0;
    entry.mFinalResult = OK;
    entry.mBufferOrdinal = ++mTotalBuffersQueued;

//mAudioQueue和mVideoQueue都是List<QueueEntry>
    if (audio) {
        Mutex::Autolock autoLock(mLock);
        mAudioQueue.push_back(entry);
        postDrainAudioQueue_l();
    } else {
        mVideoQueue.push_back(entry);
        postDrainVideoQueue();//每隔一段时间就被调用一次的
    }

    Mutex::Autolock autoLock(mLock);
    if (!mSyncQueues || mAudioQueue.empty() || mVideoQueue.empty()) {
        return;
    }

    sp<ABuffer> firstAudioBuffer = (*mAudioQueue.begin()).mBuffer;
    sp<ABuffer> firstVideoBuffer = (*mVideoQueue.begin()).mBuffer;

    if (firstAudioBuffer == NULL || firstVideoBuffer == NULL) {
        // EOS signalled on either queue.某一个queue空了
        syncQueuesDone_l();
        return;
    }

    int64_t firstAudioTimeUs;
    int64_t firstVideoTimeUs;
    CHECK(firstAudioBuffer->meta()
            ->findInt64("timeUs", &firstAudioTimeUs));
    CHECK(firstVideoBuffer->meta()
            ->findInt64("timeUs", &firstVideoTimeUs));

    int64_t diff = firstVideoTimeUs - firstAudioTimeUs;

    ALOGV("queueDiff = %.2f secs", diff / 1E6);

    if (diff > 100000ll) {
        // Audio data starts More than 0.1 secs before video.
        // Drop some audio.音频超前视频0.1s，丢掉一些音频

        (*mAudioQueue.begin()).mNotifyConsumed->post();
        mAudioQueue.erase(mAudioQueue.begin());
        return;
    }

    syncQueuesDone_l();
}

Renderer的数据输出

同样是在postDrainVideoQueue方法中，会抛出kwhatDrainVideoQueue的消息
void NuPlayer::Renderer::postDrainVideoQueue() {
….
    sp<AMessage> msg = new AMessage(kWhatDrainVideoQueue, this);
    msg->setInt32("drainGeneration", getDrainGeneration(false /* audio */));
…}
case kWhatDrainVideoQueue:
        {
            int32_t generation;
            CHECK(msg->findInt32("drainGeneration", &generation));
            if (generation != getDrainGeneration(false /* audio */)) {
                break;
            }

            mDrainVideoQueuePending = false;

            onDrainVideoQueue();

            postDrainVideoQueue();
            break;
        }
void NuPlayer::Renderer::onDrainVideoQueue() {
...
    QueueEntry *entry = &*mVideoQueue.begin();

    if (entry->mBuffer == NULL) {
        // EOS
        notifyEOS(false /* audio */, entry->mFinalResult);
...
        return;
    }

    int64_t nowUs = ALooper::GetNowUs();
    int64_t realTimeUs;
    int64_t mediaTimeUs = -1;
    if (mFlags & FLAG_REAL_TIME) {
        CHECK(entry->mBuffer->meta()->findInt64("timeUs", &realTimeUs));
    } else {
        CHECK(entry->mBuffer->meta()->findInt64("timeUs", &mediaTimeUs));

        realTimeUs = getRealTimeUs(mediaTimeUs, nowUs);
    }

    bool tooLate = false;

    if (!mPaused) {
//比较媒体时间和wall clock
        setVideoLateByUs(nowUs - realTimeUs);
        tooLate = (mVideoLateByUs > 40000);

        if (tooLate) {
            ALOGV("video late by %lld us (%.2f secs)",
                 (long long)mVideoLateByUs, mVideoLateByUs / 1E6);
        } else {
            int64_t mediaUs = 0;
            mMediaClock->getMediaTime(realTimeUs, &mediaUs);
            ALOGV("rendering video at media time %.2f secs",
                    (mFlags & FLAG_REAL_TIME ? realTimeUs :
                    mediaUs) / 1E6);...
        }
    } else {
        setVideoLateByUs(0);
...
    }

    // Always render the first video frame while keeping stats on A/V sync.
    if (!mVideoSampleReceived) {
        realTimeUs = nowUs;
        tooLate = false;
    }

    entry->mNotifyConsumed->setInt64("timestampNs", realTimeUs * 1000ll);
    entry->mNotifyConsumed->setInt32("render", !tooLate);
    entry->mNotifyConsumed->post();
    mVideoQueue.erase(mVideoQueue.begin());
    entry = NULL;

    mVideoSampleReceived = true;

    if (!mPaused) {
        if (!mVideoRenderingStarted) {
            mVideoRenderingStarted = true;
            notifyVideoRenderingStart();//刚刚开始
        }
        Mutex::Autolock autoLock(mLock);
        notifyIfMediaRenderingStarted_l();//started，和上面的notifyVideoRenderingStart走的基本是同一条路，都会post对应的kwhatxxxx msg，最后回到NuPlayer的onMessage中被处理
    }
}
NuPlayer
case kWhatRendererNotify:
        {
．．．
            int32_t what;
            CHECK(msg->findInt32("what", &what));
//根据what内容的不同能看到各种熟悉的消息
            if (what == Renderer::kWhatEOS) {
...
                if (audio) {
                    mAudioEOS = true;
                } else {
                    mVideoEOS = true;
                }

                if (finalResult == ERROR_END_OF_STREAM) {
                    ALOGV("reached %s EOS", audio ? "audio" : "video");
                } else {
                    ALOGE("%s track encountered an error (%d)",
                         audio ? "audio" : "video", finalResult);

                    notifyListener(
                            MEDIA_ERROR, MEDIA_ERROR_UNKNOWN, finalResult);
                }

                if ((mAudioEOS || mAudioDecoder == NULL)
                        && (mVideoEOS || mVideoDecoder == NULL)) {
                    notifyListener(MEDIA_PLAYBACK_COMPLETE, 0, 0);
                }
            } else if (what == Renderer::kWhatFlushComplete) {
                int32_t audio;
                CHECK(msg->findInt32("audio", &audio));

                if (audio) {
                    mAudioEOS = false;
                } else {
                    mVideoEOS = false;
                }

                ALOGV("renderer %s flush completed.", audio ? "audio" : "video");
                if (audio && (mFlushingAudio == NONE || mFlushingAudio == FLUSHED
                        || mFlushingAudio == SHUT_DOWN)) {
                    // Flush has been handled by tear down.
                    break;
                }
                handleFlushComplete(audio, false /* isDecoder */);
                finishFlushIfPossible();
            } else if (what == Renderer::kWhatVideoRenderingStart) {
//对应前面的第一个，也就是刚刚开始render
                notifyListener(MEDIA_INFO, MEDIA_INFO_RENDERING_START, 0);
            } else if (what == Renderer::kWhatMediaRenderingStart) {
                ALOGV("media rendering started");
//对应前面的第二个
                notifyListener(MEDIA_STARTED, 0, 0);
            } else if (what == Renderer::kWhatAudioTearDown) {
               ….
            }
            break;
        }
framework\av\include\media
// The player just pushed the very first video frame for rendering
enum media_info_type {
    MEDIA_INFO_RENDERING_START = 3,
}
enum media_event_type {
MEDIA_STARTED           = 6,
}

至此，就完成对android中nuplayer的ahandler机制和source\decoder\renderer三个模块的分析。欢迎互相交流学习。