Convert to FSSD Online Tool.
Classic Mac OS Computers often used a system known as SoundCap for audio files. A FSSD file is exactly what you need to play audio over the SoundCap system, and this is why so many people needed FSSD files to use on their MAC OS computers from back in the day. Not as many people use this system any longer, but there is still value to having FSSD files around in case something does need to be converted over to this format for the benefit of someone else moving forward. You never know when there may be some upside to having this file handy. If you always want to be able to convert any audio files that you would potentially have to deal with, then the answer is to go with an FSSD file to make it happen.