Fcd files

If you look around webpages for PC-Engine games you end up finding atleast a few releases in .fcd format. I grabbed the software to load it up and to convert it into an iso, however does anyone know anything about the .fcd files? Their quality? They look like they're just iso-mp3 with the mp3s missing from them, haven't tested yet tho. Some games I can only find in .fcd files, any help would be appreciated.
According to CDmage, it's a "VirtualCD uncompressed container file (*.fcd)". See pic below. I think you may be able to convert it to ISO with CDmage.


According to IsoBuster, it's a "Virtual CD-ROM, Uncompressed (*.FCD)" file:

Oops, eh DBOY was right, it's basically just an ISO file, no music with it tho, I think? Thanks for the help guys, too bad the fcd files seem useless (what good is it without the music right? heh). Eh, someone correct me if I'm wrong.