The process of reducing the bandwidth or data rate of a video stream. The analogue broadcast standards used today, PAL, NTSC and SECAM are, in fact, compression systems which reduce the data content of their original RGB sources.

Digital compression systems analyse their picture sources to find and remove redundancy and less critical information both within and between picture frames. The techniques were primarily developed for digital data transmission but have been adopted as a means of reducing transmission bandwidths and storage requirements on disks and VTRs.

A number of compression techniques are in regular use, these include ETSI, JPEG, Motion JPEG, DV, MPEG-1, MPEG-2 and MPEG-4. Where different techniques are used in the same stream, problems can occur and picture quality can suffer more than if the same method is used throughout.

The MPEG-2 family of compression schemes, which was originally designed for programme transmission, has been adapted for studio use in Betacam SX and IMX recorders.

While there is much debate, and new technologies continue to be developed, it remains true that the best compressed results are produced from the highest quality source pictures. Poor inputs do not compress well. Noise, which may be interpreted as important picture detail, is the enemy of compression.