Android 9.0 MediaPlayer播放流程分析

1.MediaPlayer初始化流程

EventHandler是后面处理数据回调的handler. 在AudioFlinger.cpp中获取nextUniqueId：

audio_unique_id_t AudioFlinger::nextUniqueId(audio_unique_id_use_t use)
{
    // This is the internal API, so it is OK to assert on bad parameter.
    LOG_ALWAYS_FATAL_IF((unsigned) use >= (unsigned) AUDIO_UNIQUE_ID_USE_MAX);
    const int maxRetries = use == AUDIO_UNIQUE_ID_USE_SESSION ? 3 : 1;
    for (int retry = 0; retry < maxRetries; retry++) {
        // The cast allows wraparound from max positive to min negative instead of abort
        uint32_t base = (uint32_t) atomic_fetch_add_explicit(&mNextUniqueIds[use],
                (uint_fast32_t) AUDIO_UNIQUE_ID_USE_MAX, memory_order_acq_rel);
        ALOG_ASSERT(audio_unique_id_get_use(base) == AUDIO_UNIQUE_ID_USE_UNSPECIFIED);
        // allow wrap by skipping 0 and -1 for session ids
        if (!(base == 0 || base == (~0u & ~AUDIO_UNIQUE_ID_USE_MASK))) {
            ALOGW_IF(retry != 0, "unique ID overflow for use %d", use);
            return (audio_unique_id_t) (base | use);
        }
    }
    // We have no way of recovering from wraparound
    LOG_ALWAYS_FATAL("unique ID overflow for use %d", use);
    // TODO Use a floor after wraparound.  This may need a mutex.
}

2. 设置播放视频路径setDataSource 接口分析

<1>. 在MediaPlayerService的setDataSource_pre中有获取IOmx监听服务是否挂掉，创建NuPlayerDriver，监听音频路由变化，创建AudioOutput：

通过上面过程可知sp p是NuPlayerDriver类：

NuPlayerDriver中的mAudioSink就是AudioOutput类，它的mPlayer是NuPlayer这个类。 

<2>. NuPlayerDriver后面调用到 NuPlayer中去了，下面看下NuPlayer的setDataSourceAsync函数