H.120
H.120 was the first digital video coding standard. It was developed by COST 211 and published in 1984 by the Comité Consultatif International Téléphonique et Télégraphique (CCITT, now ITU-T). A revision following in 1988 included contributions proposed by other organizations. The video quality was found to be inadequate, there were few implementations and there are no codecs for the format, but it provided important knowledge that led directly to its practical successors such as H.261 .
Bitstream format
H.120 data streams flowed at 1544 kbit / s with NTSC and 2048 kbit / s with PAL . Version 1 (1984) offered conditional renewal, differential pulse-code modulation , scalar quantization , coding with code words of variable length and a switch for scanning . Version 2 (1988) added motion estimation and background prediction . A final edition (without new technical content) was published in 1993 as a result of the founding of the ITU-T, which replaced the standardization organization CCITT.
Problems and experiences
H.120 was of too poor quality for practical use - it had very good spatial resolution (since DPCM works on individual pixels), but very poor temporal resolution. It became clear to researchers that one would have to encode a pixel with less than one bit on average in order to achieve an improvement in video quality without exceeding the target bit rate of the data stream. This would require the common coding of several pixels. This led to the later block-based methods such as H.261, the first common video coding standard.
swell
- ↑ Gary J. Sullivan , ITU : Overview of International Video Coding Standards (preceding H.264 / AVC) 2005, ( PDF )