Specifications

CD-i FAQ 2000 Edition Revised February 21, 2001
Latest version and more CD-i info: http://www.icdia.org
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CD-i Digital Video is based on the MPEG-1 standard, which is now extensively used in a wide
variety of applications, but it was initally developed mainly for CD-i. This standard allows CD-i to
display full resolution (384x280) moving video images in either 24, 25 or 30 frames per second.
The video is not interlaced, like with MPEG-2 used in DVD-Video. Video-quality is roughly
comparable to standard VHS. CD-i's standard ADPCM audio features can be used in conjuction
with MPEG video, but this is very unlikely since the Digital Video cartridge also provides for some
extra audio decoding schemes based on MPEG-1 layer I and II, alowing for very high quality CD-
Audio like audio that takes up only a fraction of the storage space and bandwith of CD-Audio.
MPEG-1 video is based on an encoding technique called DCT, Discrete Cosine Transform. The
basis for this encoding is the knowledge that succesive pictures in a video usually do not differ
that much from each other. Instead of encoding and storing each picture by its own, MPEG only
stores the differences between images. There are three different types of MPEG images: I or
Intra frames that consist of a full image that can be displayed without information from other
images - this is used for displaying images when performing a fast forward or reverse, P or
Progressive frames that need information from previous images and B or Bi-directional frames
that need information from both previous and future images to build a picture. As you can see, the
images are not stored in chronological order on the disc: the MPEG decoder takes care of the
decoding of the information and putting all images in correct order for display.
Digital Video is displayed on the background plane (see: 3.13 How does CD-i video work?), and
can be overlayed with images from the CD-i's Base Case video codecs, such as CLUT or RLE.