【Android多媒体】NuPlayer for HTTP Live Streaming【5】

4. start

(1) mediaplayer.cpp

status_t MediaPlayer::start()
{
    ALOGV("start");

    status_t ret = NO_ERROR;
 Mutex::Autolock _l(mLock);

    mLockThreadId = getThreadId();

    if (mCurrentState & MEDIA_PLAYER_STARTED) {
        ret = NO_ERROR;
    } else if ( (mPlayer != 0) && ( mCurrentState & ( MEDIA_PLAYER_PREPARED |
                    MEDIA_PLAYER_PLAYBACK_COMPLETE | MEDIA_PLAYER_PAUSED ) ) ) {
        mPlayer->setLooping(mLoop);
        mPlayer->setVolume(mLeftVolume, mRightVolume);
        mPlayer->setAuxEffectSendLevel(mSendLevel);
        mCurrentState = MEDIA_PLAYER_STARTED;
        ret = mPlayer->start();
        if (ret != NO_ERROR) {
            mCurrentState = MEDIA_PLAYER_STATE_ERROR;
        } else {
            if (mCurrentState == MEDIA_PLAYER_PLAYBACK_COMPLETE) {
                ALOGV("playback completed immediately following start()");
            }
        }
    } else {
        ALOGE("start called in state %d", mCurrentState);
        ret = INVALID_OPERATION;
    }

    mLockThreadId = 0;

    return ret;
}

mediaplayer将会进入MEDIA_PLAYER_STARTED状态。
（2） mediaPlayerService.cpp

status_t MediaPlayerService::Client::start()
{
    ALOGV("[%d] start", mConnId);
    sp<MediaPlayerBase> p = getPlayer();
    if (p == 0) return UNKNOWN_ERROR;
    p->setLooping(mLoop);
    return p->start();
}

（3） NuPlayerDriver.cpp

status_t NuPlayerDriver::start() {
    ALOGD("start(%p)", this);
    Mutex::Autolock autoLock(mLock);

    switch (mState) {
        case STATE_UNPREPARED:
        {
            status_t err = prepare_l();

            if (err != OK) {
                return err;
            }

            CHECK_EQ(mState, STATE_PREPARED);

            // fall through
        }

        case STATE_PREPARED:
        {
            mAtEOS = false;
            mPlayer->start();

            if (mStartupSeekTimeUs >= 0) {
                if (mStartupSeekTimeUs > 0) {
                    mPlayer->seekToAsync(mStartupSeekTimeUs);
                }

                mStartupSeekTimeUs = -1;
            }
            break;
        }

        case STATE_RUNNING:
        {
            if (mAtEOS) {
                mPlayer->seekToAsync(0);
                mAtEOS = false;
                mPositionUs = -1;
            }
            break;
        }

        case STATE_PAUSED:
        case STATE_STOPPED_AND_PREPARED:
        {
            if (mAtEOS) {
                mPlayer->seekToAsync(0);
                mAtEOS = false;
                mPlayer->resume();
                mPositionUs = -1;
            } else {
                mPlayer->resume();
            }
            break;
        }

        default:
            return INVALID_OPERATION;
    }

    mState = STATE_RUNNING;

    return OK;
}

NuPlayer中根据一些状态判断执行 start，正常情况下prepared完成后正常执行start。
（4）NuPlayerDriver往下调用的工作很多：

这里很多地方涉及到数据流，同步，丢弃，，，很多细节，出问题详细得分析调试细节。