H.120

H.120 was the first digital video encoding standard. It was developed by COST 211 and published by the CCITT in 1984, with a revision in 1988. There were few implementations, and there are no existing codecs for the format.

H.120 streams ran at 1544 kbps for NTSC and 2048 kbps for PAL. Version 1 (1984) featured conditional replenishment, differential pulse-code modulation, scalar quantization, variable-length coding and a switch for quincunx sampling. Version 2 (1988) added motion compensation and background prediction.^[1]

H.120 video was not of good enough quality for practical use — it had very good spatial resolution (as differential PCM worked on a pixel-by-pixel basis), but very poor temporal quality. To improve the video quality without exceeding the target bitrate for the stream, it would be necessary to encode using an average of less than one bit for each pixel. This would require groups of pixels to be coded together. This led to the block-based codecs that followed H.120, such as H.261, the first practical video encoding standard.^[2]

References

^ Overview of International Video Coding Standards (preceding H.264/AVC) (PDF) (Gary J. Sullivan, ITU)
^ A brief history of compression (Sundar Srinivasan, 2002)

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[1] Overview of International Video Coding Standards (preceding H.264/AVC) (PDF) (Gary J. Sullivan, ITU)

[2] A brief history of compression (Sundar Srinivasan, 2002)

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