在 Java、Android 上从 Youtube 下载视频的代码

我创建了从 Youtube 下载视频的代码，但此代码不适用于 Wi-fi 连接，但适用于移动连接。我哪里有错误？

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Vector;

import android.app.Activity;
import android.app.ProgressDialog;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.MediaController;
import android.widget.VideoView;

public class MyActivity extends Activity {

    private class ReceivingDataFromYoutube extends AsyncTask<String, Void, Void> {

        private ProgressDialog dialog = new ProgressDialog(MyActivity.this);
        private String result;

        protected void onPreExecute() {
            dialog.setMessage("Downloading...");
            dialog.show();
        }

        @Override
        protected Void doInBackground(String... arg0) {
            int begin, end;
            String tmpstr = null;
            try {
                URL url=new URL("http://www.youtube.com/watch?v=y12-1miZHLs&nomobile=1");
                HttpURLConnection con = (HttpURLConnection) url.openConnection();
                con.setRequestMethod("GET");
                InputStream stream=con.getInputStream();
                InputStreamReader reader=new InputStreamReader(stream);
                StringBuffer buffer=new StringBuffer();
                char[] buf=new char[262144];                
                int chars_read;
                while ((chars_read = reader.read(buf, 0, 262144)) != -1) {
                    buffer.append(buf, 0, chars_read);
                }
                tmpstr=buffer.toString();

                begin  = tmpstr.indexOf("url_encoded_fmt_stream_map=");
                end = tmpstr.indexOf("&", begin + 27);
                if (end == -1) {
                    end = tmpstr.indexOf("\"", begin + 27);
                }
                tmpstr = UtilClass.URLDecode(tmpstr.substring(begin + 27, end));

            } catch (MalformedURLException e) {
                throw new RuntimeException();
            } catch (IOException e) {
                throw new RuntimeException();
            }

            Vector url_encoded_fmt_stream_map = new Vector();
            begin = 0;
            end   = tmpstr.indexOf(",");

            while (end != -1) {
                url_encoded_fmt_stream_map.addElement(tmpstr.substring(begin, end));
                begin = end + 1;
                end   = tmpstr.indexOf(",", begin);
            }

            url_encoded_fmt_stream_map.addElement(tmpstr.substring(begin, tmpstr.length()));
            String result = "";
            Enumeration url_encoded_fmt_stream_map_enum = url_encoded_fmt_stream_map.elements();
            while (url_encoded_fmt_stream_map_enum.hasMoreElements()) {
                tmpstr = (String)url_encoded_fmt_stream_map_enum.nextElement();
                begin = tmpstr.indexOf("itag=");
                if (begin != -1) {
                    end = tmpstr.indexOf("&", begin + 5);

                    if (end == -1) {
                          end = tmpstr.length();
                    }

                    int fmt = Integer.parseInt(tmpstr.substring(begin + 5, end));

                    if (fmt == 35) {
                        begin = tmpstr.indexOf("url=");
                        if (begin != -1) {
                            end = tmpstr.indexOf("&", begin + 4);
                            if (end == -1) {
                               end = tmpstr.length();
                            }
                            result = UtilClass.URLDecode(tmpstr.substring(begin + 4, end));
                            this.result=result;
                            break;
                        }
                    }
                }
            }         
            try {
              URL u = new URL(result);
              HttpURLConnection c = (HttpURLConnection) u.openConnection();
              c.setRequestMethod("GET");
/*              c.setRequestProperty("Youtubedl-no-compression", "True");
              c.setRequestProperty("User-Agent", "YouTube");*/

              c.setDoOutput(true);
              c.connect();

              FileOutputStream f=new FileOutputStream(new File("/sdcard/3.flv"));

              InputStream in=c.getInputStream();
              byte[] buffer=new byte[1024];
              int sz = 0;
              while ( (sz = in.read(buffer)) > 0 ) {
                   f.write(buffer,0, sz);
              }
              f.close();
            } catch (MalformedURLException e) {
                new RuntimeException();
            } catch (IOException e) {
                new RuntimeException();
            }
            return null;
        }

        protected void onPostExecute(Void unused) {
            dialog.dismiss();
        }    

    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        new ReceivingDataFromYoutube().execute();
    }   
}  

3 steps:

1. 检查YouTube的源代码（HTML），你会得到这样的链接http%253A%252F%252Fo-o.preferred.telemar-cnf1.v18.lscache6.c.youtube.com%252Fvideoplayback ...

2. 解码url（去掉代码%2B, %25, etc), 创建解码器 http://www.w3schools.com/tags/ref_urlencode.asp与代码并使用该功能Uri.decode(url)替换无效的转义八位字节

3. 使用代码下载流：

        URL u = null;
        InputStream is = null;  
        
        try {
            u = new URL(url);
            is = u.openStream(); 
            HttpURLConnection huc = (HttpURLConnection)u.openConnection(); //to know the size of video
            int size = huc.getContentLength();                 
 
            if(huc != null) {
                String fileName = "FILE.mp4";
                String storagePath = Environment.getExternalStorageDirectory().toString();
                File f = new File(storagePath,fileName);
               
                FileOutputStream fos = new FileOutputStream(f);
                byte[] buffer = new byte[1024];
                int len1 = 0;
                if(is != null) {
                    while ((len1 = is.read(buffer)) > 0) {
                        fos.write(buffer,0, len1);  
                    }
                }
                if(fos != null) {
                    fos.close();
                }
            }                       
        } catch (MalformedURLException mue) {
            mue.printStackTrace();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        } finally {
            try {               
                if(is != null) {
                    is.close();
                }
            } catch (IOException ioe) {
                // just going to ignore this one
            }
        }

这就是全部，您可以在网上找到的大部分内容！