玩转 Android MediaPlayer之视频预加载

本文来自http://blog.csdn.net/hellogv/ ，引用必须注明出处！

       本文是在《玩转 Android MediaPlayer之Media Proxy》基础上做更进一步的开发，实现一个视频客户端很常用的功能~~~预加载。要学会本文介绍的内容，强烈建议把《玩转 Android MediaPlayer之Media Proxy》看懂，由浅入深，你懂的。

预加载，分为两类，本文介绍的是“代理服务器”这种方式：

1.边存边播：下载多少播放多少。

优点：快速加载播放，实现简单；缺点：不能拖动未存区域；适合音频媒体

2.代理服务器：预先下载媒体的头部（头部Size为 s1 byte）->监听播放器的请求，当Request的是预加载的URL->代理把媒体头部作为Response返回给播放器，并改Ranage 为 s1 byte 发送Request->代理服务器纯粹作为透传。

优点：快速加载播放，支持拖动；缺点：实现非常复杂；适合视频媒体

      预加载不仅可以缩短视频媒体的加载过程，还为“分段拼接”提供支持......通俗地说，IOS的播放器是高帅富，支持2个播放器交替播放从而无缝播放分片视频；Android的播放器是男屌丝，只能有一个实例一个个播放，切换分片视频时有明显的蛋疼感......使用预加载可以缩短停顿的时间。

先来看看预加载的效果，预加载4000ms打开视频消耗1420ms，不用预加载打开视频消耗2633ms：

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本文的源码可以到http://download.csdn.net/detail/hellogv/4486051下载，本文所用的MP4搜索自百度....

HttpGetProxy.java是本文的核心，代理服务器的主要实现，源码如下：

<span style="font-family:Comic Sans MS;font-size:18px;">/**
 * 代理服务器类
 * @author hellogv
 *
 */
public class HttpGetProxy{
    final static public String TAG = "HttpGetProxy";
    /** 链接带的端口 */
    private int remotePort=-1;
    /** 远程服务器地址 */
    private String remoteHost;
    /** 代理服务器使用的端口 */
    private int localPort;
    /** 本地服务器地址 */
    private String localHost;
    private ServerSocket localServer = null;
    /** 收发Media Player请求的Socket */
    private Socket sckPlayer = null;
    /** 收发Media Server请求的Socket */
    private Socket sckServer = null;

    private SocketAddress address;

    /**下载线程*/
    private DownloadThread download = null;
    /**
     * 初始化代理服务器
     *
     * @param localport 代理服务器监听的端口
     */
    public HttpGetProxy(int localport) {
        try {
            localPort = localport;
            localHost = C.LOCAL_IP_ADDRESS;
            localServer = new ServerSocket(localport, 1,InetAddress.getByName(localHost));
        } catch (Exception e) {
            System.exit(0);
        }
    }

    /**
     * 把URL提前下载在SD卡，实现预加载
     * @param urlString
     * @return 返回预加载文件名
     * @throws Exception
     */
    public String prebuffer(String urlString,int size) throws Exception{
        if(download!=null && download.isDownloading())
            download.stopThread(true);

        URI tmpURI=new URI(urlString);
        String fileName=ProxyUtils.urlToFileName(tmpURI.getPath());
        String filePath=C.getBufferDir()+"/"+fileName;

        download=new DownloadThread(urlString,filePath,size);
        download.startThread();

        return filePath;
    }

    /**
     * 把网络URL转为本地URL，127.0.0.1替换网络域名
     *
     * @param url网络URL
     * @return [0]:重定向后MP4真正URL，[1]:本地URL
     */
    public String[] getLocalURL(String urlString) {

        // ----排除HTTP特殊----//
        String targetUrl = ProxyUtils.getRedirectUrl(urlString);
        // ----获取对应本地代理服务器的链接----//
        String localUrl = null;
        URI originalURI = URI.create(targetUrl);
        remoteHost = originalURI.getHost();
        if (originalURI.getPort() != -1) {// URL带Port
            address = new InetSocketAddress(remoteHost, originalURI.getPort());// 使用默认端口
            remotePort = originalURI.getPort();// 保存端口，中转时替换
            localUrl = targetUrl.replace(
                    remoteHost + ":" + originalURI.getPort(), localHost + ":"
                            + localPort);
        } else {// URL不带Port
            address = new InetSocketAddress(remoteHost, C.HTTP_PORT);// 使用80端口
            remotePort = -1;
            localUrl = targetUrl.replace(remoteHost, localHost + ":"
                    + localPort);
        }

        String[] result= new String[]{targetUrl,localUrl};
        return result;
    }

    /**
     * 异步启动代理服务器
     *
     * @throws IOException
     */
    public void asynStartProxy() {

        new Thread() {
            public void run() {
                startProxy();
            }
        }.start();
    }

    private void startProxy() {
        HttpParser httpParser =null;
        int bytes_read;
        boolean enablePrebuffer=false;//必须放在这里

        byte[] local_request = new byte[1024];
        byte[] remote_reply = new byte[1024];

        while (true) {
            boolean hasResponseHeader = false;
            try {// 开始新的request之前关闭过去的Socket
                if (sckPlayer != null)
                    sckPlayer.close();
                if (sckServer != null)
                    sckServer.close();
            } catch (IOException e1) {}
            try {
                // --------------------------------------
                // 监听MediaPlayer的请求，MediaPlayer->代理服务器
                // --------------------------------------
                sckPlayer = localServer.accept();
                Log.e("TAG","------------------------------------------------------------------");
                if(download!=null && download.isDownloading())
                    download.stopThread(false);

                httpParser=new HttpParser(remoteHost,remotePort,localHost,localPort);

                ProxyRequest request = null;
                while ((bytes_read = sckPlayer.getInputStream().read(local_request)) != -1) {
                    byte[] buffer=httpParser.getRequestBody(local_request,bytes_read);
                    if(buffer!=null){
                        request=httpParser.getProxyRequest(buffer);
                        break;
                    }
                }

                boolean isExists=new File(request._prebufferFilePath).exists();
                enablePrebuffer = isExists && request._isReqRange0;//两者具备才能使用预加载
                Log.e(TAG,"enablePrebuffer:"+enablePrebuffer);
                sentToServer(request._body);
                // ------------------------------------------------------
                // 把网络服务器的反馈发到MediaPlayer，网络服务器->代理服务器->MediaPlayer
                // ------------------------------------------------------
                boolean enableSendHeader=true;
                while ((bytes_read = sckServer.getInputStream().read(remote_reply)) != -1) {
                    byte[] tmpBuffer = new byte[bytes_read];
                    System.arraycopy(remote_reply, 0, tmpBuffer, 0, tmpBuffer.length);

                    if(hasResponseHeader){
                    sendToMP(tmpBuffer);
                    }
                    else{
                        List<byte[]> httpResponse=httpParser.getResponseBody(remote_reply, bytes_read);
                        if(httpResponse.size()>0){
                            hasResponseHeader = true;
                            if (enableSendHeader) {
                                // send http header to mediaplayer
                                sendToMP(httpResponse.get(0));
                                String responseStr = new String(httpResponse.get(0));
                                Log.e(TAG+"<---", responseStr);
                            }
                            if (enablePrebuffer) {//send prebuffer to mediaplayer
                                int fileBufferSize = sendPrebufferToMP(request._prebufferFilePath);
                                if (fileBufferSize > 0) {//重新发送请求到服务器
                                    String newRequestStr = httpParser.modifyRequestRange(request._body,
                                                    fileBufferSize);
                                    Log.e(TAG + "-pre->", newRequestStr);
                                    enablePrebuffer = false;

                                    // 下次不处理response的http header
                                    sentToServer(newRequestStr);
                                    enableSendHeader = false;
                                    hasResponseHeader = false;
                                    continue;
                                }
                            }

                            //发送剩余数据
                            if (httpResponse.size() == 2) {
                                sendToMP(httpResponse.get(1));
                            }
                        }
                    }
                }
                Log.e(TAG, ".........over..........");

                // 关闭 2个SOCKET
                sckPlayer.close();
                sckServer.close();
            } catch (Exception e) {
                Log.e(TAG,e.toString());
                Log.e(TAG,ProxyUtils.getExceptionMessage(e));
            }
        }
    }

    private int sendPrebufferToMP(String fileName) throws IOException {
        int fileBufferSize=0;
        byte[] file_buffer = new byte[1024];
        int bytes_read = 0;
        FileInputStream fInputStream = new FileInputStream(fileName);
        while ((bytes_read = fInputStream.read(file_buffer)) != -1) {
            fileBufferSize += bytes_read;
            byte[] tmpBuffer = new byte[bytes_read];
            System.arraycopy(file_buffer, 0, tmpBuffer, 0, bytes_read);
            sendToMP(tmpBuffer);
        }
        fInputStream.close();

        Log.e(TAG,"读取完毕...下载:"+download.getDownloadedSize()+",读取:"+fileBufferSize);
        return fileBufferSize;
    }

    private void sendToMP(byte[] bytes) throws IOException{
            sckPlayer.getOutputStream().write(bytes);
            sckPlayer.getOutputStream().flush();
    }

    private void sentToServer(String requestStr) throws IOException{
        try {
            if(sckServer!=null)
                sckServer.close();
        } catch (Exception ex) {}
        sckServer = new Socket();
        sckServer.connect(address);
        sckServer.getOutputStream().write(requestStr.getBytes());// 发送MediaPlayer的请求
        sckServer.getOutputStream().flush();
    }
}</span>