mortal kombat armageddon and .ssf models

so I was just wondering what the hell is .ssf file? I found it to be in the wii and xbox on mortal kombat armageddon I was hoping to mod the mka models but had no idea of the format of .ssf files if anyone can help me…I havent tried the ps3 version …might be differnt but anyways if someone could convert them for me or find a .ssf opener that would be great also I tried googling it but nothing came up…