java program to convert video from wmv to avi

Hi,

i had created a java program which converts the format from wmv to avi . My programming is running fine but i want to get a confirmation message after finishing the conversion. Then i included the proc.waitFor() method for waiting till the process gets finished.

 After putting this line the program gets hanged and only continuing after terminating the program

Below is my program
package com.suku.dev;


import java.io.*;

public class TestingRuntime {
	
	public static void main(String args[])throws Exception
	
	{
		
		
		
		   Runtime rt=  Runtime.getRuntime();
		     
		     Process proc=  rt.exec("ffmpeg -i \"C:\\videos\\Nuv.wmv\"  -vcodec mpeg4 \"C:\\videos\\Sui.avi\" ");
		    
                  // if i include till above line...my program works fine
		     // If i include below lines then the program gets hanged 
		
		     InputStream stdin = proc.getInputStream();
	            InputStreamReader isr = new InputStreamReader(stdin);
	            BufferedReader br = new BufferedReader(isr);
	            String line = null;
	            System.out.println("<OUTPUT>");
	            while ( (line = br.readLine()) != null)
	                System.out.println(line);
	            System.out.println("</OUTPUT>");
	            int exitVal = proc.waitFor();            
	         
		     System.out.println("Process exitValue: " +exitVal);
	            
	      
	  
	}

}

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Please let me know the way to identify after the process gets finished
sukumarrAsked:
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WhiteMageCommented:
>>>>After putting this line the program gets hanged and only continuing after terminating the program

That's exactly what "proc.waitFor()" does.  It waits until the process (ffmpeg in this case) is terminated.

If after you have no more input, you know the process is done, then you could put this instead of proc.waitFor:

proc.destroy();
int exitVal = proc.exitValue();
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sukumarrAuthor Commented:
I tried to replace proc.waitFor() with destroy and exitValue as you said but i looks like, the process is still hanging and i'm unable to figure out at which exact place the input streaming ends

Do i need to put some Thread sleep method and check for every frequency or any other better way...
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WhiteMageCommented:
What exactly is the output of the program?  There might be a line that says when it is done.

Also, perhaps, the line is never going to null?  Does the ending "</OUTPUT>" get printed?
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objectsCommented:
you may need to also read any output written to stderr

http://helpdesk.objects.com.au/java/runtime-exec-locks-up
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WhiteMageCommented:
Yes, that is the problem.  To clarify objects vague response, use getErrorStream.  I downloaded the program and tried it and found that this was the problem before objects response.  It worked perfectly with this:

InputStream stdin = proc.getErrorStream();

Now, a problem that you might run into is that it does hang if the file already exists.  To get around that, use "-y" flag to overwrite an already existing file.  Or you could parse the input and write to the proc.getOutputStream:

//added -y flag to overwrite a file if it already exists
Process proc=  rt.exec("ffmpeg -y -i \"C:\\videos\\Nuv.wmv\"  -vcodec mpeg4 \"C:\\videos\\Sui.avi\" ");
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sukumarrAuthor Commented:
@objects

Thanks for giving hint and it worked perfectly. But i couldn't understand why it's writing to stderr instead of stdin.

@WhiteMage

Thanks for helping. Though the file exists, it's overwriting by default without providing -y flag. Anyways i appreciate your help
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