From kJams Wiki
Here's how you can get ffmpeg (open source software) into your system now:
- download VCD & MPEG Tools (Make sure you get the one "for Mac OS X"). Note: it says "15 day trial" but that does NOT affect kJams. However, I do encourage you to buy it anyway, it's a great tool for converting any VCDs that you run into.
- mount the disk image (it should mount automatically, if not, double click the .dmg file)
- if this disc image does not mount, then download it from here instead.
- drag the application to your "Applications" folder.
- Go download ffmpeg 32-bit static
- unzip the zip file
- find "ffmpeg.exe" and put it into /Users/<you>/AppData/Roaming/kJams Plugins/
That's it! You're all set, you do not need to restart kJams. kJams will "just know" where to look for the plugin.