Using FFMPEG to convert video files to FLV format

While trying to figure out how to convert video clips to FLV format I found a blog entry that mentions you can use FFMPEG and the java Runtime library to do this. If you are not familiar with FFMPEG their documentation describes it as a "very fast video and audio converter".

The blog entry function worked well with small files, but attempting to convert larger files seemed to cause the process to hang. I ran the code several times, waiting a few minutes in between each attempt. But each time the processes went out into never-never-land and .. well, never came back. I checked the Task Manager afterward and it showed several orphaned ffmpeg.exe processes. Finally I resorted to bouncing the CF Server. That did kill the orphaned processes. But I was still puzzled about why I could successfully convert the same files using ffmpeg.exe on the command line but not using Runtime.exec().

Finally I found two articles that helped explain the problem. The first entry on http://blog.taragana.com/ explains that failure to drain the input/output streams of the subprocess "may cause the subprocess to block, and even deadlock." The source of this information is an old but excellent article on www.javaworld.com . It provides a more in-depth explanation of the issue and describes how to properly use Runtime.exec().

Armed with these three references, I combined all of the suggestions and it seems to have resolved the problem. Obviously this code belongs in a function, but the sample below should give the general idea. Disclaimer: Bear in mind this is the first time I have used ffmpeg.exe and Runtime.exec() so use it at your own risk ;)

UPDATE: In my testing ffmpeg.exe appears to write to a single stream. For programs that write to both the output and error stream you need to process the streams in seperate threads to prevent blocking or deadlocks. See Runtime.exec(), mencoder and cfthread for an example.

<!--- test file paths --->
<cfset ffmpegPath = "c:\bin\ffmpeg.exe">
<cfset inputFilePath = "c:\bin\testInput.mp4">
<cfset ouputFilePath = "c:\bin\testOuput.flv">
<cfset resultLog = "c:\bin\testOuput_result.log">
<cfset errorLog = "c:\bin\testOuput_error.log">

<!--- convert the file --->
<cfset results = structNew()>
<cfscript>
    try {
        runtime = createObject("java", "java.lang.Runtime").getRuntime();
        command = '#ffmpegPath# -i "#inputFilePath#" -g 300 -y -s 300x200 -f flv -ar 44100 "#ouputFilePath#"'; 
        process = runtime.exec(#command#);
        results.errorLogSuccess = processStream(process.getErrorStream(), errorLog);
        results.resultLogSuccess = processStream(process.getInputStream(), resultLog);
        results.exitCode = process.waitFor();
    }
    catch(exception e) {
        results.status = e;    
    }
</cfscript>

<!--- display the results --->
<cfdump var="#results#">


<!--- function used to drain the input/output streams. Optionally write the stream to a file --->
<cffunction name="processStream" access="public" output="false" returntype="boolean" hint="Returns true if stream was successfully processed">
    <cfargument name="in" type="any" required="true" hint="java.io.InputStream object">
    <cfargument name="logPath" type="string" required="false" default="" hint="Full path to LogFile">
    <cfset var out = "">
    <cfset var writer = "">
    <cfset var reader = "">
    <cfset var buffered = "">
    <cfset var line = "">
    <cfset var sendToFile = false>
    <cfset var errorFound = false>
    
    <cfscript>
        if ( len(trim(arguments.logPath)) ) {
            out = createObject("java", "java.io.FileOutputStream").init(arguments.logPath);
            writer = createObject("java", "java.io.PrintWriter").init(out);
            sendToFile = true;
        }

        reader = createObject("java", "java.io.InputStreamReader").init(arguments.in);
        buffered = createObject("java", "java.io.BufferedReader").init(reader);
        line = buffered.readLine();
        while ( IsDefined("line") ) {
            if (sendToFile) {
                writer.println(line);
            }
            line = buffered.readLine();
        }    
           if (sendToFile) {
           errorFound = writer.checkError();
           writer.flush();
           writer.close();
        }
    </cfscript>
    <!--- return true if no errors found. --->
    <cfreturn (NOT errorFound)>
</cffunction>

If you are interested in testing this example, all you should need is

1. The ffmpeg binary. You can download a version at sourceforge.net

2. A sample video file

In my travels I read a tip from techrepulic.com that mentions a simple program called FLV player. The program allows you to view .flv files on a hard drive. While not the only way to view .flv files, it is a handy program.

As always, comments/corrections/suggestions are welcome. Enjoy!