【Android多媒体】NuPlayer for HTTP Live Streaming【4】

3. Prepare

（1） mediaplayer.cpp

// must call with lock held
status_t MediaPlayer::prepareAsync_l()
{
    if ( (mPlayer != 0) && ( mCurrentState & ( MEDIA_PLAYER_INITIALIZED | MEDIA_PLAYER_STOPPED) ) ) {
        mPlayer->setAudioStreamType(mStreamType);
        if (mAudioAttributesParcel != NULL) {
            mPlayer->setParameter(KEY_PARAMETER_AUDIO_ATTRIBUTES, *mAudioAttributesParcel);
        }
        mCurrentState = MEDIA_PLAYER_PREPARING;
        return mPlayer->prepareAsync();
    }
    ALOGE("prepareAsync called in state %d", mCurrentState);
    return INVALID_OPERATION;
}

（2）MediaPlayerService.cpp

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

（3）
NuPlayerDriver.cpp中的调用；

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 start
            mAtEOS = false;
            mState = STATE_STOPPED_AND_PREPARING;
            mIsAsyncPrepare = true;
            mPlayer->seekToAsync(0, true /* needNotify */);
            return OK;
        default:
            return INVALID_OPERATION;
    };
}

(4) NuPlayer往下底层完成的工作主要是，获取M3U8文件并且解析，根据解析的结果设置。

获取M3U8文件中用到了Android Socket连接读取数据的一些细节。