Video compression based on MPEG-2, with additional syntax elements that represent contributions from each previously proposed system.
A packetized, prioritized data format, providing flexibility of services and extensibility.
Audio and transmission systems had not been decided at the time of the GA agreement. Five channel audio was specified, but a decision among the Dolby AC-3, multi-channel MUSICAM audio, and MIT "AC" systems had not yet been made. Candidate transmission approaches included QAM, Spectrally-Shaped QAM, 6 VSB and 4/2 VSB. COFDM had been proposed by third parties, but was rejected as not being mature, and not offering fringe-area coverage equivalent to analog transmission. A thorough analysis of service area, interference characteristics, transmission robustness and system attributes would be performed to determine the "best approach." In the end, 1080, 720 and 480-line resolutions were implemented at various aspect ratios and frame rates, with progressive and interlaced scanning, together with 8-VSB modulation and Dolby AC-3 audio. However, the selection of transmission and audio systems was not without controversy. The choice of 8-VSB was later criticised by several groups as being inferior to COFDM under conditions of multipath interference. Improvements in receiver designs would later render this apparently moot. With MUSICAM originally faltering during GA testing, the GA issued a statement finding the MPEG-2 audio system to be "essentially equivalent" to Dolby, but only after the Dolby selection had been made. Later, a story emerged that MIT had entered into an agreement with Dolby whereupon the university would be awarded a large sum if the MUSICAM system was rejected. Following a five-year lawsuit for breach of contract, MIT and its GA representative received a total of $30 million from Dolby, after the litigants reached a last-minute out-of-court settlement. Dolby also offered an incentive for Zenith to switch their vote, however it is unknown whether they accepted the offer.
Grand Alliance Chronology
1987 - Advisory Committee on Advanced Television Service is formed, with Richard E. Wiley as chairman
1992 - All competitors announce planned improvements
1993 - ACATS Special Panel recommends retesting
1993 - Grand Alliance forms, "collaborative" phase begins
1994 - Grand Alliance system undergoes ATTC verification testing
1995 - ATSC Standard A/53 is published, incorporating Grand Alliance System
1996 - FCC Adopts ATSC A/53 as standard for the transmission of digital television, but excludes requirements with respect toscanning formats, aspect ratios, and lines of vertical resolution