From Sega Retro
Sofdec is formerly known as MPEG Sofdec a video container format developed by CRI Middleware Co. Ltd.. It supports MPEG video with a frame rate of up to 60 frames per second and ADX audio. Sofdec videos have the file extension .sfd, and are used in numerous Sega games. One of the first games to use Sofdec was Sonic Adventure on the Sega Dreamcast.