MPEG-1

MPEG-1 is the name for the first phase of MPEG work. The goal for the MPEG-1 standard was coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s. MPEG-1 Video is a format that is now not only widely used for video storage on CD but also for video storage and replay on PCs, video file transfer over the Internet, etc. MPEG-1 is e.g. used for the Video CD.

The MPEG-1 standard consists of five parts. Parts 1 (Systems), part 2 (Video) and part 3 (Audio) of the standard were approved in late 1992. The Systems part provide multiplexing and synchronisation support to elementary Audio and Video streams.

The MPEG-1 video part provides efficient encoding of non-interlaced video at around 1,15 Mbit/s with roughly VHS video quality. MPEG-1 video compression is based on the fact that there is a lot of overlap between the different pictures (frames). Only the difference between pictures is coded. MPEG-1 also uses a prediction techniques to compensate for motion, e.g to predict where a ball is which goes from side of a picture to the other side in a number of pictures.

The audio coding part of MPEG-1 consists of three operating modes called layers. The Layers-I up to Layer-III have an increasing complexity and performance. Layer-III is the mode with the highest complexity and the best performance. MPEG-1 Layer-III is better known as MP3. The Audio part provides encoding of stereo audio with transparency (i.e. subjective quality similar to the original stereo) at 384, 256 and 192 kbit/s for Layer I, II and III respectively.

The audio coding is based on a perceptual coding system. This means that the sound is analysed and only the parts of the sound that are audible for the human ear will be coded. This analysys takes into account that a loud tone can make another softer tone inaudible.

Part 4 of the MPEG-1 standard (Conformance Testing) provides methods and a reference bitstreams that can be used to test the conformance of a bitstream or of a decoder. This part was approved in late 1993. Part 5 of the standard (Reference Software) contains the programming code (C-code) that can be used as a reference for the implementation of a MPEG-1 Systems multiplexer/demultiplexer and of encoders and decoders for Audio and Video. This part of the standard was approved in 1994.