Session類

Session對(duì)象主要用于存儲(chǔ)某個(gè)會(huì)話對(duì)象所需的屬性以及配置信息埃叭，并且使用同步或者異步的方法對(duì)Session內(nèi)部的流媒體對(duì)象進(jìn)行操作和控制。

    private String mOrigin; 
    private String mDestination;
    private int mTimeToLive = 64;
    private long mTimestamp;

    private AudioStream mAudioStream = null;
    private VideoStream mVideoStream = null;

    private Callback mCallback;
    private Handler mMainHandler;
    
    private static CountDownLatch sSignal;
    private static Handler sHandler;

mMainHandler：在主線程執(zhí)行方法時(shí)用到的handler赶诊，其中所有的callback回調(diào)方法都是在主線程中回調(diào)的。

sHandler：在子線程執(zhí)行方法用到的handler园骆，大部分對(duì)Stream的操作都是在子線程中執(zhí)行舔痪。

mAudioStream和mVideoStream：音頻流媒體和視頻流媒體對(duì)象，Session對(duì)其進(jìn)行操作锌唾。

    static {
        // Creates the Thread that will be used when asynchronous methods of a Session are called
        sSignal = new CountDownLatch(1);
        new HandlerThread("net.majorkernelpanic.streaming.Session"){
            @Override
            protected void onLooperPrepared() {
                sHandler = new Handler();
                sSignal.countDown();
            }
        }.start();
    }

在靜態(tài)塊中創(chuàng)建一個(gè)子線程锄码，作為各個(gè)異步方法的執(zhí)行線程。

/** 
     * Creates a streaming session that can be customized by adding tracks.
     */
    public Session() {
        long uptime = System.currentTimeMillis();
        mMainHandler = new Handler(Looper.getMainLooper());
        mTimestamp = (uptime/1000)<<32 & (((uptime-((uptime/1000)*1000))>>32)/1000); // NTP timestamp
        mOrigin = "127.0.0.1";
        
        // Me make sure that we won't send Runnables to a non existing thread
        try {
            sSignal.await();
        } catch (InterruptedException e) {}
    }

構(gòu)造函數(shù)中sSignal.await();是等待上面的子線程Looper創(chuàng)建完畢后，再往下執(zhí)行主線程巍耗。

/** Deletes all existing tracks & release associated resources. */
    public void release() {
        removeAudioTrack();
        removeVideoTrack();
        sHandler.getLooper().quit();
    }

在最后release時(shí)秋麸，釋放音頻流和視頻流，并且需要將sHandler的looper釋放掉炬太，這個(gè)方法是在主線程中執(zhí)行灸蟆。

對(duì)于Stream進(jìn)行操作的一系列方法，由于篇幅原因不在這里展開列舉亲族，其實(shí)大多數(shù)的操作動(dòng)作都是由sHandler.post發(fā)出消息炒考，在子線程中執(zhí)行的；而動(dòng)作執(zhí)行完成的回調(diào)都是由mMainHandler.post發(fā)出消息霎迫，在主線程中執(zhí)行回調(diào)斋枢。

SessionBuilder類

SessionBuilder類就是用來(lái)構(gòu)建Session對(duì)象。SessionBuilder采用了單例模式知给，需要使用getInstance()方法來(lái)獲取到實(shí)例對(duì)象瓤帚。

// Default configuration
    private VideoQuality mVideoQuality = VideoQuality.DEFAULT_VIDEO_QUALITY;
    private AudioQuality mAudioQuality = AudioQuality.DEFAULT_AUDIO_QUALITY;
    private Context mContext;
    private int mVideoEncoder = VIDEO_H263; 
    private int mAudioEncoder = AUDIO_AMRNB;
    private int mCamera = CameraInfo.CAMERA_FACING_BACK;
    private int mTimeToLive = 64;
    private int mOrientation = 0;
    private boolean mFlash = false;
    private SurfaceView mSurfaceView = null;
    private String mOrigin = null;
    private String mDestination = null;
    private Session.Callback mCallback = null;

構(gòu)建Session時(shí)默認(rèn)的配置參數(shù)，可以通過(guò)set方法設(shè)置參數(shù)值涩赢。

/**
     * Creates a new {@link Session}.
     * @return The new Session
     * @throws IOException 
     */
    public Session build() {
        Session session;

        session = new Session();
        session.setOrigin(mOrigin);
        session.setDestination(mDestination);
        session.setTimeToLive(mTimeToLive);
        session.setCallback(mCallback);

        switch (mAudioEncoder) {
        case AUDIO_AAC:
            AACStream stream = new AACStream();
            session.addAudioTrack(stream);
            if (mContext!=null) 
                stream.setPreferences(PreferenceManager.getDefaultSharedPreferences(mContext));
            break;
        case AUDIO_AMRNB:
            session.addAudioTrack(new AMRNBStream());
            break;
        }

        switch (mVideoEncoder) {
        case VIDEO_H263:
            session.addVideoTrack(new H263Stream(mCamera));
            break;
        case VIDEO_H264:
            H264Stream stream = new H264Stream(mCamera);
            if (mContext!=null) 
                stream.setPreferences(PreferenceManager.getDefaultSharedPreferences(mContext));
            session.addVideoTrack(stream);
            break;
        }

        if (session.getVideoTrack()!=null) {
            VideoStream video = session.getVideoTrack();
            video.setFlashState(mFlash);
            video.setVideoQuality(mVideoQuality);
            video.setSurfaceView(mSurfaceView);
            video.setPreviewOrientation(mOrientation);
            video.setDestinationPorts(5006);
        }

        if (session.getAudioTrack()!=null) {
            AudioStream audio = session.getAudioTrack();
            audio.setAudioQuality(mAudioQuality);
            audio.setDestinationPorts(5004);
        }

        return session;

    }

SessionBuilder使用了build模式來(lái)構(gòu)建Session戈次，build()方法創(chuàng)建Session對(duì)象并對(duì)其附上已設(shè)置完成的參數(shù)值，mAudioEncoder和mVideoEncoder用于設(shè)置音頻和視頻的編碼格式筒扒。

這篇文章我們大致了解了Session內(nèi)部機(jī)制（兩個(gè)handler分別負(fù)責(zé)同步操作和異步操作）和構(gòu)建方式（SessionBuilder的build()方法）怯邪，下一步我們將逐步分析Stream類和MediaStream類。