Moving .Jar files to .Mp4

.jar files are java. Not sure you'll be able to get the audio out of it with a tool to just extract the audio.

Your only option is likely going to be something like Wiretap Studio.

I'd suggest Audio Hijack Pro, but I've been pretty unhappy with Rogue Amoeba's support lately and their blame Apple attitude for a lot of things.

So, Wiretap Studio would allow you to play the audio files from the webpage (since it's java, i assume you listen to it via the web browser) then use Wiretap Studio to record the audio playing in that application (browser).

It does have to happen real time rather than accelerated. But it would do what you're asking.

 

Something else you can try

rename the .jar to .zip

Then unzip it and see if the audio file is contained inside it.

Possible, but you should probably cross your fingers on this one.