Crashes instantly upon opening. I had to access the console log to get this info.

[0x0-0x154154].ContentaConverterBASIC[2651] usage: dirname path
[0x0-0x154154].ContentaConverterBASIC[2651] Exception in thread "Thread-0"
[0x0-0x154154].ContentaConverterBASIC[2651] java.lang.NoClassDefFoundError: com/contenta/converter/Main
[0x0-0x154154].ContentaConverterBASIC[2651] Caused by: java.lang.ClassNotFoundException: com.contenta.converter.Main
[0x0-0x154154].ContentaConverterBASIC[2651] at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
[0x0-0x154154].ContentaConverterBASIC[2651] at java.security.AccessController.doPrivileged(Native Method)
[0x0-0x154154].ContentaConverterBASIC[2651] at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
[0x0-0x154154].ContentaConverterBASIC[2651] at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
[0x0-0x154154].ContentaConverterBASIC[2651] at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
[0x0-0x154154].ContentaConverterBASIC[2651] at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
com.apple.launchd.peruser.501[164] ([0x0-0x154154].ContentaConverterBASIC[2651]) Exited with exit code: 1

I dont know if you've tried this, but you would also want to make sure plugging in some headphones wont effectively 'mute' the speakers.