使用ffmpeg转码时怎么判断转码是否已经结束了呢

process = Runtime.getRuntime().exec(cmd);
br = new BufferedReader(new InputStreamReader(process.getInputStream(), "UTF-8"));
while (br.readLine() != null) ;

public class MediocreExecJavac {
    public void runCmd(String command) {

        try {

            Runtime rt = Runtime.getRuntime();

            Process proc = rt.exec(command);

            InputStream stderr = proc.getErrorStream();

            InputStreamReader isr = new InputStreamReader(stderr);

            BufferedReader br = new BufferedReader(isr);

            String line = null;

           while ( (line = br.readLine()) != null)

                System.out.println(line);
           int exitVal = proc.waitFor();

            System.out.println("Process exitValue: " + exitVal);

       } catch (Throwable t) {

           t.printStackTrace();

        }

   }

   public boolean transfer(String infile,String outfile) {

        String avitoflv = "ffmpeg -i "+infile+" -ar 22050 -ab 56 -f flv -y -s 320x240 "+outfile;

        String flvto3gp = "ffmpeg -i " + infile + " -ar 8000 -ac 1 -acodec amr_nb -vcodec h263 -s 176x144 -r 12 -b 30 -ab 12 " + outfile;

        String avito3gp = "ffmpeg -i " + infile + " -ar 8000 -ac 1 -acodec amr_nb -vcodec h263 -s 176x144 -r 12 -b 30 -ab 12 " + outfile;

        String avitojpg = "ffmpeg -i " + infile + " -y -f image2 -ss 00:00:10 -t 00:00:01 -s 350x240 " + outfile;
        try {

            Runtime rt = Runtime.getRuntime();

            Process proc = rt.exec(avitoflv);

            InputStream stderr = proc.getErrorStream();

            InputStreamReader isr = new InputStreamReader(stderr);

            BufferedReader br = new BufferedReader(isr);

            String line = null;



            while ( (line = br.readLine()) != null)

                System.out.println(line);

           int exitVal = proc.waitFor();

           System.out.println("Process exitValue: " + exitVal);

       } catch (Throwable t) {

            t.printStackTrace();

           return false;

        }

        return true;

    }

    public static String readFile(String fileName,int id) {

        String dataStr = "";

       FileInputStream fis = null;
       try {

            FileReader file = new FileReader(fileName);//建立FileReader对象，并实例化为fr

           BufferedReader br=new BufferedReader(file);//建立BufferedReader对象，并实例化为br

            String Line=br.readLine();//从文件读取一行字符串

           dataStr=Line;

            br.close();//关闭BufferedReader对象

       } catch(Exception e) {
        } finally {

           try {

                if(fis!=null)

                    fis.close();

            } catch(Exception e) {}

        }

        return dataStr;
    }

    public String readtime(String file) {

        String str="/root/Desktop/info.txt";

        String timelen = "";

        String cmd = "timelen "+file;
        runCmd(cmd);
        timelen=readFile(str,1);
        return timelen;

    }

    public static void main(String args[]) {

        MediocreExecJavac me = new MediocreExecJavac();

        String infile = "/root/Desktop/a.mp4";
       String outfile = "/root/Desktop/1.flv";

       String timelen = me.readtime(infile);

      System.out.println("timelen is :" + timelen);
        if(me.transfer(infile,outfile)) {
            System.out.println("the transfer is ok!");

        } else {

           System.out.println("the transfer is error!");

       }

    }

}