MediaPlayer(二)--MediaPlayer基本框架

小蚂蚁与大象

发布于 2020-04-17 11:40:07

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代码可运行

文章被收录于专栏：构建FFmpeg Android播放器构建FFmpeg Android播放器

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代码可运行

MediaPlayer涉及的的文件路径

这里参考的是android8.1 的代码 JAVA类的路径： frameworks/base/media/java/android/media/MediaPlayer.java

JNI路径： frameworks/base/media/jni/android_media_MediaPlayer.cpp 编译为 libmedia_jni.so

native 层的接口 frameworks/av/media/libmedia 编译为 libmedia.so

native层服务： frameworks/av/media/libmediaplayerservice/ 编译为 libmediaplayerservice.so

MediePlayer框架

MediaPlayerArch.png

MediaPlayer是给应用层提供的接口，通过jni调用native层，native层又采用C/S框架，通过binder调用到service端， servcie端最终调用到本地播放器NuPlayer。 Binder是android普遍采用的架构，这里应该主要也是为了对资源和client进行统一管理。不过笔者不太明白为什么不跟其他模块一样在java层使用binder通讯呢 NuPlayer是andriod原生的播放器，芯片厂家一般会替换成自己的播放器。MediaPlayerService实际上持有的是MediaPlayerFactory， NuPlayer通过MediaPlayerFactory创建出来的，是典型的工厂设计模式

MediaPlayerFactory.png

IFactory为MediaPlayerFactory的内部类，芯片厂家只要创建自己的factory和player就能替换掉android原生的nuplayer

Nuplayer的注册创建过程

MediaPlayerService 在构造函数中会去创建各个Player Factory, 并保存到sFactoryMap 中, 后续创建播放器会通过对应的type去获取到对应的factory。

MediaPlayerService::MediaPlayerService()
{
    ALOGV("MediaPlayerService created");
    mNextConnId = 1;

    MediaPlayerFactory::registerBuiltinFactories();
}

void MediaPlayerFactory::registerBuiltinFactories() {
    Mutex::Autolock lock_(&sLock);

    if (sInitComplete)
        return;

    IFactory* factory = new NuPlayerFactory();
    if (registerFactory_l(factory, NU_PLAYER) != OK)
        delete factory;
    factory = new TestPlayerFactory();
    if (registerFactory_l(factory, TEST_PLAYER) != OK)
        delete factory;
#ifdef USE_FFPLAYER
    factory = new FFPlayerFactory();
    if (registerFactory_l(factory,FF_PLAYER) != OK)
        delete factory;
#endif

    sInitComplete = true;
}

status_t MediaPlayerFactory::registerFactory_l(IFactory* factory,
                                               player_type type) {
    if (NULL == factory) {
        ALOGE("Failed to register MediaPlayerFactory of type %d, factory is"
              " NULL.", type);
        return BAD_VALUE;
    }

    if (sFactoryMap.indexOfKey(type) >= 0) {
        ALOGE("Failed to register MediaPlayerFactory of type %d, type is"
              " already registered.", type);
        return ALREADY_EXISTS;
    }

    if (sFactoryMap.add(type, factory) < 0) {
        ALOGE("Failed to register MediaPlayerFactory of type %d, failed to add"
              " to map.", type);
        return UNKNOWN_ERROR;
    }

    return OK;
}

播放器实例会在上层调用setDataSource时调用到createPlayer创建，MediaPlayerFactory会根据playerType，调用对应的factory去创建player

sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
{
    // determine if we have the right player type
    sp<MediaPlayerBase> p = getPlayer();
    if ((p != NULL) && (p->playerType() != playerType)) {
        ALOGV("delete player");
        p.clear();
    }
    if (p == NULL) {
        p = MediaPlayerFactory::createPlayer(playerType, this, notify, mPid);
    }

    if (p != NULL) {
        p->setUID(mUid);
    }

    return p;
}

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