Java Process Builder runs ffmpeg commands very slowly

userkORx 0
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I'm trying to run ffmpeg in Java using ProcessBuilder. I'm on Windows. It works fine. But not sure why it's much slower than when I just run the same command in command prompt or PowerShell.

Why is it? Is there any ways to increase the speed?

processBuilder.command("C:\\Windows\\System32\\cmd.exe", "/c","ffmpeg.exe", "-y", "-i", video,"-vf","scale=720:-1","out.mp4");
    processBuilder.redirectErrorStream(true);
    try {
                process = processBuilder.start();
                BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
                
                String line="";
                while ((line = reader.readLine()) != null) {
                        System.out.println(line);
        }
        } catch (Exception e) {
            System.err.println("Error in processBuilder. ");
        }
bufferedreader processbuilder cmd ffmpeg java
1 Answers

You have two starts, delete the first or the redirect will not work:

process = processBuilder.start();

If your sub-process is quite verbose the problem may simply be System.out.println() as multiple line output to some Windows cmd / terminals can be exceptionally slow. You can verify if this is the case by commenting out the print, or capture to File based output before start:

processBuilder.redirectOutput(new File("stdout.log"));

Don't forget to add status check at the end and cross check rc with ffmpeg documentation:

int rc = process.waitFor();
DuncG0
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