【stagefrightpalyer】2 awesomeplayer结构分析

概述

通过分析stagefrightplayer代码可以知道,stagefrightplayer 是awesomeplayer的封装,实际的工作都由awsomeplayer完成

一个典型的播放器框架包括如下组成部分:

stream: 流类型,一般有文件类型、网络流等

demuxer:解复用模块,主要是通过分析带播放的数据,得到基本信息,如audio video的基本参数等,还负责分解audio和video数据,为下层模块提供边界完整的包

decoder:解码模块,从demuxer模块得到原始的audio-packet video-packet,解码成实际可播放或者显示的 pcm以及 yuv(或rgb)等

render : 显示模块,将pcm以及yuv(或rgb)在声卡上播放以及在画布上显示

其他部分: 主要是一些播放器的机制,如同步、切音轨、pause-resume,seek等

 

stagefrightplayer作为媒体播放器,自然也包括上面这些基础模块,这里主要是从总体上分析stagefrightplayer的结构

本篇主要介绍如下内容

1、awesomeplayer总体结构

2、awesomeplayer的工作方式

3、awesomeplayer代码分析

4、其他事件分析

下面详细讲解

 

1、awesomeplayer的总体结构

 整体结构如下图

【stagefrightpalyer】2 awesomeplayer结构分析_第1张图片

这里先简单做几点说明,后面文章会对每个模块进行详细分析

数据结构

mExtractor -- MediaExtractor

mAudioTrack&mVideoTrack -- MediaSource

说明:

    awesomeplayer利用mExtractor 和 mAudioTrack&mVideoTrack等成员来完成 数据的解析和读取。

    对于每种格式的媒体文件,均需要实现一个MediaExtractor 的子类,例如AVI文件的extractor类为AVIExtractor,在构造函数中完成对数据的解析,主要信息由:媒体文件中流的个数,音频流的采样率、声道数、量化位数等,视频流的宽度、高度、帧率等信息。

    对于每个流,都对应一个单独的MediaSource,以avi为例,为AVISource,MediaSource 提供了状态接口(start stop),数据读取接口(read),参数查询接口(getFormat)。其中调用一次read函数,可以认为是读取对应的一个数据包。

    一般而言,由于MediaExtractor 负责解析工作,因此MediaSource 的read操作一般也通过MediaExtractor 的接口获取offset和size,对于MediaSource 只进行数据的读取工作,不参与解析。

    这里mAudioTrack&mVideoTrack 分别对应的媒体文件中选中的音频流和视频流,从代码知道,选取规则是第一个视频和第一个音频。

 

mAudioSource &mVideoSource -- MediaSource

说明:

    这里mAudioSource &mVideoSource可以认为是awesomeplayer与decoder之间的桥梁,awesomeplayer从mAudioSource &mVideoSource 里获取数据,进行播放,而decoder则负责解码并向mAudioSource &mVideoSource 填充数据

    这里awesomeplayer与decoder的通信是通过OMXClient mClient; 成员进行的,OMX*解码器是一个服务,每个awesomeplayer对象都包含一个单独的client端与之交互。

 

 mAudioPlayer -- AudioPlayer

说明:

    mAudioPlayer 是负责音频输出的模块,主要封装关系为:mAudioPlayer->mAudioSink->mAudioTrack(这里的mAudioTrack 与前面不同,此处为AudioTrack对象)

    实际进行音频播放的对象为mAudioTrack-audioflinger 结构

 

mVideoRenderer -- AwesomeRenderer

说明:

    mVideoRenderer 是负责视频显示的模块,封装关系为:mVideoRenderer ->mTarget(SoftwareRenderer)->mNativeWindow 【注】此处理解不清晰

    最后依靠surfaceflinger来显示

 

2、awesomeplayer的工作方式

    上面介绍了,awesomeplayer中的主要成员,下面介绍下awesomeplayer依靠哪种方式驱动主要成员协同工作。

    这里就不得不提到android中的一个类即TimedEventQueue,这是一个消息处理类,在之前的文章中有介绍过,【参考文章:TimedEventQueue】

    这里通过对每个事件消息提供一个fire函数完成相应的操作。而整个播放过程的驱动方式为递归的触发mVideoEvent 事件来控制媒体文件的播放。

    ​​说明:详细可参考下面的代码分析

    awesomeplayer中主要有如下几个事件

    sp<TimedEventQueue::Event> mVideoEvent = new AwesomeEvent(this, &AwesomePlayer::onVideoEvent);   --- 显示一帧画面,并负责同步处理
    sp<TimedEventQueue::Event> mStreamDoneEvent = new AwesomeEvent(this, &AwesomePlayer::onStreamDone);   -- 播放结束的处理

    sp<TimedEventQueue::Event> mBufferingEvent = new AwesomeEvent(this, &AwesomePlayer::onBufferingUpdate); -- cache数据
    sp<TimedEventQueue::Event> mCheckAudioStatusEvent = new AwesomeEvent(this, &AwesomePlayer::onCheckAudioStatus); -- 监测audio 状态:seek以及播放结束
    sp<TimedEventQueue::Event> mVideoLagEvent = new AwesomeEvent(this, &AwesomePlayer::onVideoLagUpdate);  -- 监测video 解码性能

    sp<TimedEventQueue::Event> mAsyncPrepareEvent = new AwesomeEvent(this, &AwesomePlayer::onPrepareAsyncEvent); -- 完成prepareAsync工作

这里会在下面的代码分析中看到具体的工作流程

3、awesomeplayer代码分析

下面通过分析实际的代码进一步对awesomaplayer的机构和流程加深理解。

这里我们还是按照播放一个媒体文件的实际调用步骤来分析,具体调用顺序如下

StagefrightPlayer player =newStagefrightPlayer();
player->setDataSource(*)
player->prepareAsync()
player->start();


下面详细介绍每个调用.[说明]仅为说明流程,不严谨

3.1 构造函数

StagefrightPlayer::StagefrightPlayer()
    : mPlayer(newAwesomePlayer) {
    ALOGV("StagefrightPlayer");
    mPlayer->setListener(this);
}

这里stagefrightplayer是awesomeplayer 封装。主要看下awesomaplayer的构造函数

AwesomePlayer::AwesomePlayer()
    : mQueueStarted(false),
      mUIDValid(false),
      mTimeSource(NULL),
      mVideoRenderingStarted(false),
      mVideoRendererIsPreview(false),
      mAudioPlayer(NULL),
      mDisplayWidth(0),
      mDisplayHeight(0),
      mVideoScalingMode(NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW),
      mFlags(0),
      mExtractorFlags(0),
      mVideoBuffer(NULL),
      mDecryptHandle(NULL),
      mLastVideoTimeUs(-1),
      mTextDriver(NULL) {
    CHECK_EQ(mClient.connect(), (status_t)OK);
    DataSource::RegisterDefaultSniffers();
    mVideoEvent =newAwesomeEvent(this, &AwesomePlayer::onVideoEvent);
    mVideoEventPending =false;
    mStreamDoneEvent =newAwesomeEvent(this, &AwesomePlayer::onStreamDone);
    mStreamDoneEventPending =false;
    mBufferingEvent =newAwesomeEvent(this, &AwesomePlayer::onBufferingUpdate);
    mBufferingEventPending =false;
    mVideoLagEvent =newAwesomeEvent(this, &AwesomePlayer::onVideoLagUpdate);
    mVideoEventPending =false;
    mCheckAudioStatusEvent =newAwesomeEvent(
            this, &AwesomePlayer::onCheckAudioStatus);
    mAudioStatusEventPending =false;
    reset();
}

在awesomeplayer的构造函数中主要就是做些准备工作:如创立event对象,并提供fire函数,设置对应的各个状态变量

还有一点需要注意的是 mClient.connect() 建立了awesomeplayer与omx解码器之间的链接,后面介绍解码器模块的时候会详细介绍

 

3.2 setDataSource

说明:这里以本地文件为例,传入参数为文件句柄

具体代码如下:

status_t StagefrightPlayer::setDataSource(intfd, int64_t offset, int64_t length) {
    ALOGV("setDataSource(%d, %lld, %lld)", fd, offset, length);
    returnmPlayer->setDataSource(dup(fd), offset, length);
}

继续深入看awesomeplayer

status_t AwesomePlayer::setDataSource(
        intfd, int64_t offset, int64_t length) {
    Mutex::Autolock autoLock(mLock);
 
    reset_l();
 
    sp<DataSource> dataSource =newFileSource(fd, offset, length);
 
    status_t err = dataSource->initCheck();
 
    if(err != OK) {
        returnerr;
    }
 
    mFileSource = dataSource;
 
    {
        Mutex::Autolock autoLock(mStatsLock);
        mStats.mFd = fd;
        mStats.mURI = String8();
    }
 
    returnsetDataSource_l(dataSource);
}

首先建立文件对应的datasource,这里是FileSource,提供对实际文件的读写,seek等

dataSource->initCheck 是判断合法性,这里是判断fd是否有效

主要工作在setDataSource_l(dataSource); 完成,继续跟进代码

status_t AwesomePlayer::setDataSource_l(
        constsp<DataSource> &dataSource) {
    sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource);
 
    if(extractor == NULL) {
        returnUNKNOWN_ERROR;
    }
 
    if(extractor->getDrmFlag()) {
        checkDrmStatus(dataSource);
    }
 
    returnsetDataSource_l(extractor);
}

这里依据提供的dataSource建立对应的MediaExtractor,这里说明下,有了dataSource,就可以从文件中读取数据,就可以通过分析文件头解析出文件具体是哪种格式,然后建立相应的MediaExtractor

之前有介绍,在MediaExtractor 建立的时候便完成了对文件的解析,包括流数量,各个流的具体信息等,下面就可以直接使用了

这里不再深入了,等讲解MediaExtractor的时候再介绍

下面进入 setDataSource_l(extractor); ,代码比较多,我们分开来看

status_t AwesomePlayer::setDataSource_l(constsp<MediaExtractor> &extractor) {
    // Attempt to approximate overall stream bitrate by summing all
    // tracks' individual bitrates, if not all of them advertise bitrate,
    // we have to fail.
 
    int64_t totalBitRate =0;
 
    mExtractor = extractor;
    for(size_t i =0; i < extractor->countTracks(); ++i) {
        sp<MetaData> meta = extractor->getTrackMetaData(i);
 
        int32_t bitrate;
        if(!meta->findInt32(kKeyBitRate, &bitrate)) {
            constchar *mime;
            CHECK(meta->findCString(kKeyMIMEType, &mime));
            ALOGV("track of type '%s' does not publish bitrate", mime);
 
            totalBitRate = -1;
            break;
        }
 
        totalBitRate += bitrate;
    }
 
    mBitrate = totalBitRate;


前面说了,MediaExtractor 建立后,我们也就拿到了对应的信息,

这里流数量可以通过extractor->countTracks() 得到,每个流对应的信息存储在一个MetaData中通过extractor->getTrackMetaData(i); 得到

上面这段代码是通过解析每个流的bitrate来得到整个文件的波特率(当有一个流没有设置此参数时,则设置totalBitRate =-1),最后赋值给成员mBitrate

下面是选取待播放的视频流和音频流的过程

bool haveAudio = false;
bool haveVideo = false;
for (size_t i = 0; i < extractor->countTracks(); ++i) {
    sp<MetaData> meta = extractor->getTrackMetaData(i);
 
    constchar *_mime;
    CHECK(meta->findCString(kKeyMIMEType, &_mime));
 
    String8 mime = String8(_mime);

 首先是对每个流,先获取kKeyMIMEType参数,此参数标示了流类型是音频 视频 还是字幕,看下具体分析

if (!haveVideo && !strncasecmp(mime.string(), "video/",6)) {
            setVideoSource(extractor->getTrack(i));
            haveVideo =true;
 
            // Set the presentation/display size
            int32_t displayWidth, displayHeight;
            bool success = meta->findInt32(kKeyDisplayWidth, &displayWidth);
            if(success) {
                success = meta->findInt32(kKeyDisplayHeight, &displayHeight);
            }
            if(success) {
                mDisplayWidth = displayWidth;
                mDisplayHeight = displayHeight;
            }
 
            {
                Mutex::Autolock autoLock(mStatsLock);
                mStats.mVideoTrackIndex = mStats.mTracks.size();
                mStats.mTracks.push();
                TrackStat *stat =
                    &mStats.mTracks.editItemAt(mStats.mVideoTrackIndex);
                stat->mMIME = mime.string();
            }
        }

上面是视频的情况,如果是视频,设置video标志haveVideo为true,后面获取对应的参数,主要是宽度、高度

然后将此流信息保存在mStates.mTracks中

else if (!haveAudio && !strncasecmp(mime.string(), "audio/", 6)) {
            setAudioSource(extractor->getTrack(i));
            haveAudio =true;
            mActiveAudioTrackIndex = i;
 
            {
                Mutex::Autolock autoLock(mStatsLock);
                mStats.mAudioTrackIndex = mStats.mTracks.size();
                mStats.mTracks.push();
                TrackStat *stat =
                    &mStats.mTracks.editItemAt(mStats.mAudioTrackIndex);
                stat->mMIME = mime.string();
            }
 
            if(!strcasecmp(mime.string(), MEDIA_MIMETYPE_AUDIO_VORBIS)) {
                // Only do this for vorbis audio, none of the other audio
                // formats even support this ringtone specific hack and
                // retrieving the metadata on some extractors may turn out
                // to be very expensive.
                sp<MetaData> fileMeta = extractor->getMetaData();
                int32_t loop;
                if(fileMeta != NULL
                        && fileMeta->findInt32(kKeyAutoLoop, &loop) && loop !=0) {
                    modifyFlags(AUTO_LOOPING, SET);
                }
            }
         }

上面是音频的情况,也是保存参数,设置hasAudio标志,并保存在mStates.mTracks中

这里单独处理的vorbis的case,没去深究

MIMETYPE_TEXT_3GPP)) {
            addTextSource_l(i, extractor->getTrack(i));
        }

在后面是处理字幕的情况,这里android字幕还不完善,后面完善后在系统讲下。

if (!haveAudio && !haveVideo) {
        if(mWVMExtractor != NULL) {
            returnmWVMExtractor->getError();
        }else{
            returnUNKNOWN_ERROR;
        }
    }
 
    mExtractorFlags = extractor->flags();
 
    returnOK;
}

最后更新下flags就结束了

这里总结下,setdatasource的主要工作就是解析文件头信息,获取媒体文件的各个流的基本参数 

 

3.3 prepareAsync

在之前的译文【MediaPlayer类介绍】中,解释过prepare和prepareAsync的区别,即一个是同步的一个是异步的,但做的事情是一样的

看下入口代码

status_t StagefrightPlayer::prepareAsync() {
    returnmPlayer->prepareAsync();
}

继续进入awesomeplayer

status_t AwesomePlayer::prepareAsync() {
    ATRACE_CALL();
    Mutex::Autolock autoLock(mLock);
 
    if(mFlags & PREPARING) {
        returnUNKNOWN_ERROR; // async prepare already pending
    }
 
    mIsAsyncPrepare =true;
    returnprepareAsync_l();
}

继续

status_t AwesomePlayer::prepareAsync_l() {
    if(mFlags & PREPARING) {
        returnUNKNOWN_ERROR; // async prepare already pending
    }
 
    if(!mQueueStarted) {
        mQueue.start();
        mQueueStarted =true;
    }
 
    modifyFlags(PREPARING, SET);
    mAsyncPrepareEvent =newAwesomeEvent(
            this, &AwesomePlayer::onPrepareAsyncEvent);
 
    mQueue.postEvent(mAsyncPrepareEvent);
 
    returnOK;
}

这里比较重要,首先如果发现mQueue还没有启动,则启动,启动之后就可以处理事件了

随后构造了mAsyncPrepareEvent 时间,提供了事件响应函数AwesomePlayer::onPrepareAsyncEvent,最后将消息发送出去,mQueue.postEvent(mAsyncPrepareEvent);

消息发送后,便会触发消息响应函数,看下onPrepareAsyncEvent具体实现

void AwesomePlayer::onPrepareAsyncEvent() {
    Mutex::Autolock autoLock(mLock);
 
    if(mFlags & PREPARE_CANCELLED) {
        ALOGI("prepare was cancelled before doing anything");
        abortPrepare(UNKNOWN_ERROR);
        return;
    }
 
    if(mUri.size() >0) {
        status_t err = finishSetDataSource_l();
 
        if(err != OK) {
            abortPrepare(err);
            return;
        }
    }
 
    if(mVideoTrack != NULL && mVideoSource == NULL) {
        status_t err = initVideoDecoder();
 
        if(err != OK) {
            abortPrepare(err);
            return;
        }
    }
 
    if(mAudioTrack != NULL && mAudioSource == NULL) {
        status_t err = initAudioDecoder();
 
        if(err != OK) {
            abortPrepare(err);
            return;
        }
    }
 
    modifyFlags(PREPARING_CONNECTED, SET);
 
    if(isStreamingHTTP()) {
        postBufferingEvent_l();
    }else{
        finishAsyncPrepare_l();
    }
}

这里主要是完成了如下几个重要步骤: -- initVideoDecoder -- initAudioDecoder --  finishAsyncPrepare_l

说明:还有个方法为finishSetDataSource_l ,这里由于调用的setdatasource传入的是fd,因此不会初始化mUri,因此不会调用,看实现可以知道,其功能与setDataSource(int fd, int64_t offset, int64_t length)一致

这里我们分三个小节来详细介绍

说明:这里我们不考虑drm的情况,这里只介绍结构和流程,因此会忽略一些代码

(1) initVideoDecoder

status_t AwesomePlayer::initVideoDecoder(uint32_t flags) {
    ATRACE_CALL();
 
 
 
    ALOGV("initVideoDecoder flags=0x%x", flags);
    mVideoSource = OMXCodec::Create(
            mClient.interface(), mVideoTrack->getFormat(),
            false,// createEncoder
            mVideoTrack,
            NULL, flags, USE_SURFACE_ALLOC ? mNativeWindow : NULL);
 
    if(mVideoSource != NULL) {
        int64_t durationUs;
        if(mVideoTrack->getFormat()->findInt64(kKeyDuration, &durationUs)) {
            Mutex::Autolock autoLock(mMiscStateLock);
            if(mDurationUs <0|| durationUs > mDurationUs) {
                mDurationUs = durationUs;
            }
        }
 
        status_t err = mVideoSource->start();
 
        if(err != OK) {
            ALOGE("failed to start video source");
            mVideoSource.clear();
            returnerr;
        }
    }

上面是函数的主体部分,主要就是调用OMXCodec::Create创建解码器,将mClient作为参数传入作为桥梁,以及将mVideoTrack作为数据源提供给解码器模块

并将返回的MediaSource对象保存在mVideoSource中,这样后面awesomeplayer便可以从mVideoSource中获取数据进行显示了

创建完毕后,接着就启动解码器进行解码

 
 
if (mVideoSource != NULL) {

        const char *componentName;

        CHECK(mVideoSource->getFormat()

                ->findCString(kKeyDecoderComponent, &componentName));

 

        {

            Mutex::Autolock autoLock(mStatsLock);

            TrackStat *stat = &mStats.mTracks.editItemAt(mStats.mVideoTrackIndex);

 

            stat->mDecoderName = componentName;

        }

 

        static const char *kPrefix = "OMX.Nvidia.";

        static const char *kSuffix = ".decode";

        static const size_t kSuffixLength = strlen(kSuffix);

 

        size_t componentNameLength = strlen(componentName);

 

        if (!strncmp(componentName, kPrefix, strlen(kPrefix))

                && componentNameLength >= kSuffixLength

                && !strcmp(&componentName[

                    componentNameLength - kSuffixLength], kSuffix)) {

            modifyFlags(SLOW_DECODER_HACK, SET);

        }

    }

 

    return mVideoSource != NULL ? OK : UNKNOWN_ERROR;

}

余下的代码就是将解码器信息等更新到mStats成员中

 

(2) initAudioDecoder

这里audio部分与video部分一样,也是创建解码器,以及保存信息,代码如下

status_t AwesomePlayer::initAudioDecoder() {
    ATRACE_CALL();
 
    sp<MetaData> meta = mAudioTrack->getFormat();
 
    constchar *mime;
    CHECK(meta->findCString(kKeyMIMEType, &mime));
 
    if(!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_RAW)) {
        mAudioSource = mAudioTrack;
    }else{
        mAudioSource = OMXCodec::Create(
                mClient.interface(), mAudioTrack->getFormat(),
                false,// createEncoder
                mAudioTrack);
    }
 
    if(mAudioSource != NULL) {
        int64_t durationUs;
        if(mAudioTrack->getFormat()->findInt64(kKeyDuration, &durationUs)) {
            Mutex::Autolock autoLock(mMiscStateLock);
            if(mDurationUs <0|| durationUs > mDurationUs) {
                mDurationUs = durationUs;
            }
        }
 
        status_t err = mAudioSource->start();
 
        if(err != OK) {
            mAudioSource.clear();
            returnerr;
        }
    }elseif(!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_QCELP)) {
        // For legacy reasons we're simply going to ignore the absence
        // of an audio decoder for QCELP instead of aborting playback
        // altogether.
        returnOK;
    }
 
    if(mAudioSource != NULL) {
        Mutex::Autolock autoLock(mStatsLock);
        TrackStat *stat = &mStats.mTracks.editItemAt(mStats.mAudioTrackIndex);
        constchar *component;
        if(!mAudioSource->getFormat()
                ->findCString(kKeyDecoderComponent, &component)) {
            component ="none";
        }
 
        stat->mDecoderName = component;
    }
 
    returnmAudioSource != NULL ? OK : UNKNOWN_ERROR;
}

(3) finishAsyncPrepare_l

 经过上面的步骤,解码器已经可以正常的解码,并将解码后的数据分别放在mAudioSource和mVideoSource中

后面就是prepare的收尾工作,代码如下

void AwesomePlayer::finishAsyncPrepare_l() {
    if(mIsAsyncPrepare) {
        if(mVideoSource == NULL) {
            notifyListener_l(MEDIA_SET_VIDEO_SIZE,0,0);
        }else{
            notifyVideoSize_l();
        }
 
        notifyListener_l(MEDIA_PREPARED);
    }
 
    mPrepareResult = OK;
    modifyFlags((PREPARING|PREPARE_CANCELLED|PREPARING_CONNECTED), CLEAR);
    modifyFlags(PREPARED, SET);
    mAsyncPrepareEvent = NULL;
    mPreparedCondition.broadcast();
}

首先通过notifyVideoSize_l更新宽度、高度信息,还有rotate等信息,确定最终的输出样式

还有就是更新状态以及flags等 

最后通过mPreparedCondition.broadcast();将prepare 成功的消息发送出去。【Condition用法参考文章:condition & mutex】

其作用主要用在,当调用的是prepare的方法的时候,需要等待prepareasync执行完毕后返回,即block调用方式

因此有如下代码:

status_t AwesomePlayer::prepare_l() {
    if(mFlags & PREPARED) {
        returnOK;
    }
 
    if(mFlags & PREPARING) {
        returnUNKNOWN_ERROR;
    }
 
    mIsAsyncPrepare =false;
    status_t err = prepareAsync_l();
 
    if(err != OK) {
        returnerr;
    }
 
    while(mFlags & PREPARING) {
        mPreparedCondition.wait(mLock);
    }
 
    returnmPrepareResult;
}

这里broadcast 会使得mPreparedCondition.wait(mLock);退出。还有这里还有一点是,循环里还会检测awesomeplayer的状态,在上面的finishAsyncPrepare_l 中也会通过modifyFlags(PREPARED, SET); 修改

这里就完成的所有的准备工作。

3.4 start

 入口

status_t StagefrightPlayer::start() {
    ALOGV("start");
 
    returnmPlayer->play();
}

继续,

status_t AwesomePlayer::play() {
    ATRACE_CALL();
 
    Mutex::Autolock autoLock(mLock);
 
    modifyFlags(CACHE_UNDERRUN, CLEAR);
 
    returnplay_l();
}

awesomeplayer中play->play_l,继续看play_l

status_t AwesomePlayer::play_l() {
    modifyFlags(SEEK_PREVIEW, CLEAR);
 
    if(mFlags & PLAYING) {
        returnOK;
    }
 
    if(!(mFlags & PREPARED)) {
        status_t err = prepare_l();
 
        if(err != OK) {
            returnerr;
        }
    }
 
    modifyFlags(PLAYING, SET);
    modifyFlags(FIRST_FRAME, SET);

这里首先判断状态是否是PREPARED,如果不是则重新调用prepare_l方法

如果是,则修改状态为PLAYING

if (mAudioSource != NULL) {
    if(mAudioPlayer == NULL) {
        if(mAudioSink != NULL) {
            bool allowDeepBuffering;
            int64_t cachedDurationUs;
            bool eos;
            if(mVideoSource == NULL
                    && (mDurationUs > AUDIO_SINK_MIN_DEEP_BUFFER_DURATION_US ||
                    (getCachedDuration_l(&cachedDurationUs, &eos) &&
                    cachedDurationUs > AUDIO_SINK_MIN_DEEP_BUFFER_DURATION_US))) {
                allowDeepBuffering =true;
            }else{
                allowDeepBuffering =false;
            }
 
            mAudioPlayer =newAudioPlayer(mAudioSink, allowDeepBuffering,this);
            mAudioPlayer->setSource(mAudioSource);
 
            mTimeSource = mAudioPlayer;
 
            // If there was a seek request before we ever started,
            // honor the request now.
            // Make sure to do this before starting the audio player
            // to avoid a race condition.
            seekAudioIfNecessary_l();
        }
    }
 
    CHECK(!(mFlags & AUDIO_RUNNING));
 
    if(mVideoSource == NULL) {
        // We don't want to post an error notification at this point,
        // the error returned from MediaPlayer::start() will suffice.
 
        status_t err = startAudioPlayer_l(
                false/* sendErrorNotification */);
 
        if(err != OK) {
            deletemAudioPlayer;
            mAudioPlayer = NULL;
 
            modifyFlags((PLAYING | FIRST_FRAME), CLEAR);
 
            if(mDecryptHandle != NULL) {
                mDrmManagerClient->setPlaybackStatus(
                        mDecryptHandle, Playback::STOP,0);
            }
 
            returnerr;
        }
    }
}

上面代码是创建audio的输出模块,mAudioPlayer

代码也比较清晰,即构建mAudioPlayer对象,将mAudioSink作为参数传入,之前有介绍,实际的播放顺序是 mAudioPlayer ->mAudioSink ->mAudioTrack(不要混淆,此处类是AudioTrack)

还有设置mAudioPlayer的数据源即mAudioSource

接着如果只有audio 即mVideoSource == NULL,则直接启动播放

if (mTimeSource == NULL && mAudioPlayer == NULL) {
    mTimeSource = &mSystemTimeSource;
}

上面代码是设置同步时钟的,这里如果mAudioPlayer存在的话,以audio为基准进行播放,否则以系统时钟为基准控制播放

if (mVideoSource != NULL) {
        // Kick off video playback
        postVideoEvent_l();
 
        if(mAudioSource != NULL && mVideoSource != NULL) {
            postVideoLagEvent_l();
        }
    }
 
    if(mFlags & AT_EOS) {
        // Legacy behaviour, if a stream finishes playing and then
        // is started again, we play from the start...
        seekTo_l(0);
    }
 
    uint32_t params = IMediaPlayerService::kBatteryDataCodecStarted
        | IMediaPlayerService::kBatteryDataTrackDecoder;
    if((mAudioSource != NULL) && (mAudioSource != mAudioTrack)) {
        params |= IMediaPlayerService::kBatteryDataTrackAudio;
    }
    if(mVideoSource != NULL) {
        params |= IMediaPlayerService::kBatteryDataTrackVideo;
    }
    addBatteryData(params);
 
    returnOK;
}

执行到此就是说audio video都是存在的,首先是触发mVideoEvent消息,之后触发mVideoLagEvent消息,最后seek 到0位置就开始播放了

 

下面分三个小节分别介绍,mAudioSink如何传入, postVideoEvent_l和postVideoLagEvent_l

(1)mAudioSink如何传入

在最初的mediaplayerservice中,调用setdatasource操作代码如下

sp<MediaPlayerBase> MediaPlayerService::Client::setDataSource_pre(
        player_type playerType)
{
    ALOGV("player type = %d", playerType);
 
    // create the right type of player
    sp<MediaPlayerBase> p = createPlayer(playerType);
    if(p == NULL) {
        returnp;
    }
 
    if(!p->hardwareOutput()) {
        mAudioOutput =newAudioOutput(mAudioSessionId);
        static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);
    }
 
    returnp;
}

这里会构造一个AudioOutput对象传入作为mAudioSink

 

(2)postVideoEvent

代码如下

void AwesomePlayer::postVideoEvent_l(int64_t delayUs) {
    ATRACE_CALL();
 
    if(mVideoEventPending) {
        return;
    }
 
    mVideoEventPending =true;
    mQueue.postEventWithDelay(mVideoEvent, delayUs <0?10000: delayUs);
}

主要就是触发mVideoEvent事件,其响应函数是AwesomePlayer::onVideoEvent,

void AwesomePlayer::onVideoEvent() {
    ATRACE_CALL();
    Mutex::Autolock autoLock(mLock);
    if(!mVideoEventPending) {
        // The event has been cancelled in reset_l() but had already
        // been scheduled for execution at that time.
        return;
    }
    mVideoEventPending =false;
 
    if(mSeeking != NO_SEEK) {
        if(mVideoBuffer) {
            mVideoBuffer->release();
            mVideoBuffer = NULL;
        }
 
        if(mSeeking == SEEK && isStreamingHTTP() && mAudioSource != NULL
                && !(mFlags & SEEK_PREVIEW)) {
            // We're going to seek the video source first, followed by
            // the audio source.
            // In order to avoid jumps in the DataSource offset caused by
            // the audio codec prefetching data from the old locations
            // while the video codec is already reading data from the new
            // locations, we'll "pause" the audio source, causing it to
            // stop reading input data until a subsequent seek.
 
            if(mAudioPlayer != NULL && (mFlags & AUDIO_RUNNING)) {
                mAudioPlayer->pause();
 
                modifyFlags(AUDIO_RUNNING, CLEAR);
            }
            mAudioSource->pause();
        }
    }

首先是判断是否需要seek,若需要seek,则先pause住audio,先完成video的seek,后面再seek audio

if (!mVideoBuffer) {
        MediaSource::ReadOptions options;
        if(mSeeking != NO_SEEK) {
            ALOGV("seeking to %lld us (%.2f secs)", mSeekTimeUs, mSeekTimeUs / 1E6);
 
            options.setSeekTo(
                    mSeekTimeUs,
                    mSeeking == SEEK_VIDEO_ONLY
                        ? MediaSource::ReadOptions::SEEK_NEXT_SYNC
                        : MediaSource::ReadOptions::SEEK_CLOSEST_SYNC);
        }
        for(;;) {
            status_t err = mVideoSource->read(&mVideoBuffer, &options);
            options.clearSeekTo();
 
            if(err != OK) {
                CHECK(mVideoBuffer == NULL);
 
                if(err == INFO_FORMAT_CHANGED) {
                    ALOGV("VideoSource signalled format change.");
 
                    notifyVideoSize_l();
 
                    if(mVideoRenderer != NULL) {
                        mVideoRendererIsPreview =false;
                        initRenderer_l();
                    }
                    continue;
                }
 
                // So video playback is complete, but we may still have
                // a seek request pending that needs to be applied
                // to the audio track.
                if(mSeeking != NO_SEEK) {
                    ALOGV("video stream ended while seeking!");
                }
                finishSeekIfNecessary(-1);
 
                if(mAudioPlayer != NULL
                        && !(mFlags & (AUDIO_RUNNING | SEEK_PREVIEW))) {
                    startAudioPlayer_l();
                }
 
                modifyFlags(VIDEO_AT_EOS, SET);
                postStreamDoneEvent_l(err);
                return;
            }
 
            if(mVideoBuffer->range_length() ==0) {
                // Some decoders, notably the PV AVC software decoder
                // return spurious empty buffers that we just want to ignore.
 
                mVideoBuffer->release();
                mVideoBuffer = NULL;
                continue;
            }
 
            break;
        }
 
        {
            Mutex::Autolock autoLock(mStatsLock);
            ++mStats.mNumVideoFramesDecoded;
        }
    }

上面代码可分为两部分,第一部分判断是否需要seek,若需要则设置option

第二部分是从mAudioSource中读取一帧画面,这里读取的时候会将option传入,如果需要seek,则读取出的数据直接就是seek后的解码数据,Nice

中间还有些小细节:如果数据读取失败,则检查宽度高度是否发生变化,否则即video播放完毕了,设置EOF标记,并触发mStreamDoneEvent消息

int64_t timeUs;
CHECK(mVideoBuffer->meta_data()->findInt64(kKeyTime, &timeUs));
 
mLastVideoTimeUs = timeUs;
 
if (mSeeking == SEEK_VIDEO_ONLY) {
    if(mSeekTimeUs > timeUs) {
        ALOGI("XXX mSeekTimeUs = %lld us, timeUs = %lld us",
             mSeekTimeUs, timeUs);
    }
}
 
{
    Mutex::Autolock autoLock(mMiscStateLock);
    mVideoTimeUs = timeUs;
}
 
SeekType wasSeeking = mSeeking;
finishSeekIfNecessary(timeUs);

上面代码是当成功读取到一帧数据,则拿出此数据的时间戳信息

之前说如果有seek请求,则先pause住audio,读取seek的video数据,拿到第一帧数据后,以此数据为标准,来seek audio,此处finishSeekIfNecessary便是完成此功能,读者可自行阅读,比较简单

if (mAudioPlayer != NULL && !(mFlags & (AUDIO_RUNNING | SEEK_PREVIEW))) {
    status_t err = startAudioPlayer_l();
    if(err != OK) {
        ALOGE("Starting the audio player failed w/ err %d", err);
        return;
    }
}
 
if ((mFlags & TEXTPLAYER_INITIALIZED)
        && !(mFlags & (TEXT_RUNNING | SEEK_PREVIEW))) {
    mTextDriver->start();
    modifyFlags(TEXT_RUNNING, SET);
}

在后面是如果有audio则启动audio播放,如果有subtitle则启动播放

TimeSource *ts =
    ((mFlags & AUDIO_AT_EOS) || !(mFlags & AUDIOPLAYER_STARTED))
        ? &mSystemTimeSource : mTimeSource;
 
if (mFlags & FIRST_FRAME) {
    modifyFlags(FIRST_FRAME, CLEAR);
    mSinceLastDropped =0;
    mTimeSourceDeltaUs = ts->getRealTimeUs() - timeUs;
}
 
int64_t realTimeUs, mediaTimeUs;
if (!(mFlags & AUDIO_AT_EOS) && mAudioPlayer != NULL
    && mAudioPlayer->getMediaTimeMapping(&realTimeUs, &mediaTimeUs)) {
    mTimeSourceDeltaUs = realTimeUs - mediaTimeUs;
}
 
if (wasSeeking == SEEK_VIDEO_ONLY) {
    int64_t nowUs = ts->getRealTimeUs() - mTimeSourceDeltaUs;
 
    int64_t latenessUs = nowUs - timeUs;
 
    ATRACE_INT("Video Lateness (ms)", latenessUs / 1E3);
 
    if(latenessUs >0) {
        ALOGI("after SEEK_VIDEO_ONLY we're late by %.2f secs", latenessUs / 1E6);
    }
}

上面是更新时间信息,首先获取时钟源,系统时钟或者audio时钟

如果是第一帧画面则mTimeSourceDeltaUs=ts->getRealTimeUs() - timeUs;

如果不是第一帧画面则:mTimeSourceDeltaUs = realTimeUs - mediaTimeUs;

这里先解释下这几个变量即调用的意义

ts->getRealTimeUs() :这是通过计算播放了多少audio帧换算出来的实际时间

timeUs :这是下一帧画面的时间戳

realTimeUs = mPositionTimeRealUs 这是从mAudioplayer中获取的信息(如果有audio的话),是当前播放位置的时间

mPositionTimeMediaUs : 下一包音频数据的时间戳

通过这些信息便可以计算出当前播放位置:这里对于第一包audio或者video不是0的情况读者可自己思考上述机制是如何保证正常运行的。

后面单独分析mAudioPlayer的时候会仔细分析。

下面wasSeeking == SEEK_VIDEO_ONLY先忽略掉,继续

if (wasSeeking == NO_SEEK) {
    // Let's display the first frame after seeking right away.
 
    int64_t nowUs = ts->getRealTimeUs() - mTimeSourceDeltaUs;
 
    int64_t latenessUs = nowUs - timeUs;
 
    ATRACE_INT("Video Lateness (ms)", latenessUs / 1E3);
 
    if(latenessUs > 500000ll
            && mAudioPlayer != NULL
            && mAudioPlayer->getMediaTimeMapping(
                &realTimeUs, &mediaTimeUs)) {
        if(mWVMExtractor == NULL) {
            ALOGI("we're much too late (%.2f secs), video skipping ahead",
                 latenessUs / 1E6);
 
            mVideoBuffer->release();
            mVideoBuffer = NULL;
 
            mSeeking = SEEK_VIDEO_ONLY;
            mSeekTimeUs = mediaTimeUs;
 
            postVideoEvent_l();
            return;
        }else{
            // The widevine extractor doesn't deal well with seeking
            // audio and video independently. We'll just have to wait
            // until the decoder catches up, which won't be long at all.
            ALOGI("we're very late (%.2f secs)", latenessUs / 1E6);
        }
    }
 
    if(latenessUs >40000) {
        // We're more than 40ms late.
        ALOGV("we're late by %lld us (%.2f secs)",
             latenessUs, latenessUs / 1E6);
 
        if(!(mFlags & SLOW_DECODER_HACK)
                || mSinceLastDropped > FRAME_DROP_FREQ)
        {
            ALOGV("we're late by %lld us (%.2f secs) dropping "
                 "one after %d frames",
                 latenessUs, latenessUs / 1E6, mSinceLastDropped);
 
            mSinceLastDropped =0;
            mVideoBuffer->release();
            mVideoBuffer = NULL;
 
            {
                Mutex::Autolock autoLock(mStatsLock);
                ++mStats.mNumVideoFramesDropped;
            }
 
            postVideoEvent_l();
            return;
        }
    }
 
    if(latenessUs < -10000) {
        // We're more than 10ms early.
        postVideoEvent_l(10000);
        return;
    }
}

上面代码和之前的时间处理要结合起来看,计算出来mTimeSourceDeltaUs之后,就可以分析播放信息如:

当前播放进度,即int64_t nowUs = ts->getRealTimeUs() - mTimeSourceDeltaUs;

播放的latency: int64_t latenessUs = nowUs - timeUs; (这里timeUs是下一帧的时间戳)

下面是处理latency过大的情况:这里比对参考是audio或者系统时钟,即与音视频同步的处理,当视频与音频或者与系统时钟相差太多时

超过500000ll US,则seek到对应位置;超过40000 则丢帧处理;当比参考时钟早了10ms,则通过postVideoEvent_l(10000);延迟触发下一次的mVideoEvent

if ((mNativeWindow != NULL)
            && (mVideoRendererIsPreview || mVideoRenderer == NULL)) {
        mVideoRendererIsPreview =false;
 
        initRenderer_l();
    }
 
    if(mVideoRenderer != NULL) {
        mSinceLastDropped++;
        mVideoRenderer->render(mVideoBuffer);
        if(!mVideoRenderingStarted) {
            mVideoRenderingStarted =true;
            notifyListener_l(MEDIA_INFO, MEDIA_INFO_RENDERING_START);
        }
 
    }
 
    mVideoBuffer->release();
    mVideoBuffer = NULL;
 
    if(wasSeeking != NO_SEEK && (mFlags & SEEK_PREVIEW)) {
        modifyFlags(SEEK_PREVIEW, CLEAR);
        return;
    }
 
    postVideoEvent_l();
}

最后就是显示此帧画面了,当播放过程一切正常时,则显示此帧画面,并通过 postVideoEvent_l();触发下一次的mVideoEvent事件

 

分析到这里大家应该明白,awesoemplayer的播放驱动机制即通过递归的调用postVideoEvent_l(); 来完成

而且由于postVideoEvent_l(); 里有延迟触发消息机制,因此也不会阻塞。

 

(3)postVideoLagEvent

看下此事件的处理方法

void AwesomePlayer::onVideoLagUpdate() {
    Mutex::Autolock autoLock(mLock);
    if(!mVideoLagEventPending) {
        return;
    }
    mVideoLagEventPending =false;
 
    int64_t audioTimeUs = mAudioPlayer->getMediaTimeUs();
    int64_t videoLateByUs = audioTimeUs - mVideoTimeUs;
 
    if(!(mFlags & VIDEO_AT_EOS) && videoLateByUs > 300000ll) {
        ALOGV("video late by %lld ms.", videoLateByUs / 1000ll);
 
        notifyListener_l(
                MEDIA_INFO,
                MEDIA_INFO_VIDEO_TRACK_LAGGING,
                videoLateByUs / 1000ll);
    }
 
    postVideoLagEvent_l();
}

这里主要是为了更新信息,看定义

    // The video is too complex for the decoder: it can't decode frames fast
    // enough. Possibly only the audio plays fine at this stage.
    MEDIA_INFO_VIDEO_TRACK_LAGGING = 700,

可以知道当视频解码速度不够时,会通知上层,decoder不给力

 

4、其他事件分析

到这里,整个播放器的流程就讲完了,但有些事件我们并没有涉及,这里也把脉络说一下

之前我们列出了所有的事件,这里再列举一下

    sp<TimedEventQueue::Event> mVideoEvent = new AwesomeEvent(this, &AwesomePlayer::onVideoEvent);
    sp<TimedEventQueue::Event> mStreamDoneEvent = new AwesomeEvent(this, & AwesomePlayer::onStreamDone);   

    sp<TimedEventQueue::Event> mBufferingEvent = new AwesomeEvent(this, & AwesomePlayer::onBufferingUpdate);
    sp<TimedEventQueue::Event> mCheckAudioStatusEvent = new AwesomeEvent(this, & AwesomePlayer::onCheckAudioStatus);
    sp<TimedEventQueue::Event> mVideoLagEvent = new AwesomeEvent(this, & AwesomePlayer::onVideoLagUpdate);

    sp<TimedEventQueue::Event> mAsyncPrepareEvent = new AwesomeEvent(this, &AwesomePlayer::onPrepareAsyncEvent);

上面分析了mAsyncPrepareEvent mVideoLagEvent mVideoEvent ,下面分析下其他几个事件

 

(1)mStreamDoneEvent 

这里是当vidoe播放结束后会触发,在onVideoEvent中当读取帧数据失败时

void AwesomePlayer::onStreamDone() {
    // Posted whenever any stream finishes playing.
    ATRACE_CALL();
 
    Mutex::Autolock autoLock(mLock);
    if(!mStreamDoneEventPending) {
        return;
    }
    mStreamDoneEventPending =false;
 
    if(mStreamDoneStatus != ERROR_END_OF_STREAM) {
        ALOGV("MEDIA_ERROR %d", mStreamDoneStatus);
 
        notifyListener_l(
                MEDIA_ERROR, MEDIA_ERROR_UNKNOWN, mStreamDoneStatus);
 
        pause_l(true/* at eos */);
 
        modifyFlags(AT_EOS, SET);
        return;
    }
 
    constbool allDone =
        (mVideoSource == NULL || (mFlags & VIDEO_AT_EOS))
            && (mAudioSource == NULL || (mFlags & AUDIO_AT_EOS));
 
    if(!allDone) {
        return;
    }
 
    if((mFlags & LOOPING)
            || ((mFlags & AUTO_LOOPING)
                && (mAudioSink == NULL || mAudioSink->realtime()))) {
        // Don't AUTO_LOOP if we're being recorded, since that cannot be
        // turned off and recording would go on indefinitely.
 
        seekTo_l(0);
 
        if(mVideoSource != NULL) {
            postVideoEvent_l();
        }
    }else{
        ALOGV("MEDIA_PLAYBACK_COMPLETE");
        notifyListener_l(MEDIA_PLAYBACK_COMPLETE);
 
        pause_l(true/* at eos */);
 
        modifyFlags(AT_EOS, SET);
    }
}

这里主要功能如下:

判断是否真的播放完毕了

若播放完毕了,是否需要循环,若需要则调用seekTo_l(0)继续播放

否则,通知上层本次播放结束,发送MEDIA_PLAYBACK_COMPLETE给调用者

 

(2)mBufferingEvent

awesomeplayer中通过调用postBufferingEvent_l来触发此事件

作用是为了cache数据

调用的位置有

void AwesomePlayer::onPrepareAsyncEvent() {
 
    *****************
 
    if(isStreamingHTTP()) {
        postBufferingEvent_l();
    }else{
        finishAsyncPrepare_l();
    }
}

当时网络流的时候,先缓冲一部分数据,看下具体实现

void AwesomePlayer::postBufferingEvent_l() {
    if(mBufferingEventPending) {
        return;
    }
    mBufferingEventPending =true;
    mQueue.postEventWithDelay(mBufferingEvent, 1000000ll);
}

首先修改标志位mBufferingEventPending,之后触发消息

这里就不贴代码了,说说原理:当需要cache数据的时候,在onPrepareAsyncEvent调用postBufferingEvent_l 后onPrepareAsyncEvent 就结束了。由于此时解码器已经开始解码,即数据链路已经建立

因此会不断的进行 读数据-解码的操作,而在onBufferingUpdate响应函数中,会先pause住输出,等数据缓存足够了之后,调用finishAsyncPrepare_l等完成prepareAsync的操作

 

(3)mCheckAudioStatusEvent

触发此事件的调用顺序是:

startAudioPlayer_l->postAudioSeekComplete->postCheckAudioStatusEvent

fillBuffer(mAudioPlayer)->postAudioEOS->postCheckAudioStatusEvent

作用就是查询audio的状态

代码如下

void AwesomePlayer::postCheckAudioStatusEvent(int64_t delayUs) {
    Mutex::Autolock autoLock(mAudioLock);
    if(mAudioStatusEventPending) {
        return;
    }
    mAudioStatusEventPending =true;
    // Do not honor delay when looping in order to limit audio gap
    if(mFlags & (LOOPING | AUTO_LOOPING)) {
        delayUs =0;
    }
    mQueue.postEventWithDelay(mCheckAudioStatusEvent, delayUs);
}

 具体响应代码

void AwesomePlayer::onCheckAudioStatus() {
    {
        Mutex::Autolock autoLock(mAudioLock);
        if(!mAudioStatusEventPending) {
            // Event was dispatched and while we were blocking on the mutex,
            // has already been cancelled.
            return;
        }
 
        mAudioStatusEventPending =false;
    }
 
    Mutex::Autolock autoLock(mLock);
 
    if(mWatchForAudioSeekComplete && !mAudioPlayer->isSeeking()) {
        mWatchForAudioSeekComplete =false;
 
        if(!mSeekNotificationSent) {
            notifyListener_l(MEDIA_SEEK_COMPLETE);
            mSeekNotificationSent =true;
        }
 
        mSeeking = NO_SEEK;
    }
 
    status_t finalStatus;
    if(mWatchForAudioEOS && mAudioPlayer->reachedEOS(&finalStatus)) {
        mWatchForAudioEOS =false;
        modifyFlags(AUDIO_AT_EOS, SET);
        modifyFlags(FIRST_FRAME, SET);
        postStreamDoneEvent_l(finalStatus);
    }
}


作用一个是用来监测seek是否结束,第二个是播放是否到了结尾,这里与video一样,播放结束也会触发postStreamDoneEvent_l

 

【结束】


文章系原创,转载请注明出处!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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