Sega CD refers to an attachment to the Sega Genesis console unit. The attachment is a single-speed CD drive with its own processor which expanded both the computing and storage capability of the standard Genesis unit. Many games released for the Sega CD unit were heavy on FMV. Many Sega CD games used the SGA format for multimedia, but were by no means limited to it. Other formats included early Sega FILM variations with video FourCCs of 'Sega' and 'Seg4'. Many games advertised "Cinepak for Sega" on their box copy.
Another notable fact about multimedia on the Sega CD is that many games transported PCM audio formatted as sign/magnitude PCM data. This implies that the Sega CD unit probably had hardware to play this type of audio directly.