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Although JPEG provides enough compression
to allow single-frame digitized images to fit on disk drives, it soon
became apparent that full-motion pictures were going to need much
greater compression to be useful on current technology.
Therefore, the MPEG format was developed with a compression algorithm
that delivers compression ratios up to 200:1, with high-quality video
and audio.
As with JPEG, MPEG removes redundant picture information from individual scenes. However, instead of simply removing redundant information from within a single frame, the MPEG compression scheme removes redundant information from consecutive scenes. In addition, the MPEG methodology compresses only key objects within a frame every 15th frame. Between these key frames, only the information that changes from frame-to-frame is recorded. The MPEG standard includes specifications for audio compression and decompression in both MPEG1 and 2. MPEG1 supports a quality that is very similar to CD-quality stereo output, at data rates between 128kbps and 256kbps. The MPEG 2 specification supports CD-quality surround-sound (four-channel) output. |