The Grand Alliance has submitted the complete specification for their proposed system to the FCC and it is beginning to be tested. It supports the following spatial formats:

1280x720 :    23.976/24Hz  progressive
              29.97/30Hz   progressive
              59.94/60Hz   progressive

1920x1080 :   23.976/24Hz  progressive
              29.97/30Hz   progressive
              59.94/60Hz   interlaced
1440x1080 :   59.94/60Hz   interlaced

The formats are all progressive-scan, with the exception of 1920 x 1080 x 60. That one is planned to start out interlaced, as there is currently no way to acceptably compress 1920x1080x60 proscan into a 6 MHz channel. There has also been talk of NTSC-compatible versions of each of these (23.98, 29.97, and 59.94 fps) in addition to the integer rates listed above.

Broadcast HDTV will, by FCC mandate, occupy a single 6 MHz channel, starting out in the currently unused and taboo channels and coexisting with the current NTSC broadcasters. The video compression will be a variant of MPEG-2, and the audio will be Dolby AC-3 (basically a five-channel system) . The modulation scheme will be a variation of the 16-VSB scheme orignally proposed by Zenith. All data packets would be 188 bytes long, with 4 bytes of header/descriptor and 184 bytes of payload.

All of this is as currently proposed by the so-called Grand Alliance which consists of the earlier proponent groups which came up with the final four systems considered by ACATS and the FCC. The major players include AT&T, Zenith, General Instruments, MIT, NBC, the Sarnoff labs, and others. There is still a lot of debate going on - the standard is not yet all that firm. Major areas of debate include whether or not there is truly a need for an interlaced transmission format, and the exact set of permissible transmission frame rates. It seems that there is currently pretty wide agreement on the formats themselves and the encoding schemes, although there is some disagreement even here - for example, the motion picture community has proposed abandoning the 16:9 aspect ratio in favor of 2:1, at least for transmission. And, of course, all of the above applies only to the North American standard (the U.S. and Canada have formally agreed to use a single standard, and Mexico is expected to follow); Japan and Europe are certainly watching the U.S. process closely, but it is not certain that there will be a single worldwide broadcast standard.

As has been mentioned, testing is underway in a limited form now; the actual date of full-blown HDTV in the U.S. is anyone's guess, but we should see the release of the final standard within the next 1-2 years (just a guess, your mileage may vary), and then some consumer use close to the end of the decade. It seems that the FCC plan was to eliminate NTSC altogether by 2008, although this was based on an HDTV start-up in 1995 (meaning that once HDTV got going, NTSC would be on a 13-year countdown to extinction). Whether or not this will actually happen is also open to debate, however, there may be an NTSC-like (at least in HxV pixel count) digital transmission format, we'll just have to see.