Originally Posted by rbinck

It is very confusing to many people. Partly because they can not reconize where the bars originate. They can originate at the TV station, the set top box or the TV itself.

First of all it should be stressed that HD is not part of the mandate. Also it should be stressed that 16:9 aspect ratio is also not part of the mandate. The only thing that is mandated is the change to digital transmission and there are 18 available formats that stations can choose for their particular transmissions.

There seems to be four formats that has been currently adopted by stations:
640x480p @ 60fps EDTV - 4:3
704x480p @ 60fps EDTV - 16:9
1280x720p @ 60fps HDTV - 16:9
1920x1080i @ 30fps HDTV - 16:9

My NBC affiliate for example uses the 1920x1080i @30fps for their 2-1 HD subchannel and for their two other subchannels 2-2 & 2-3 they use the 640x480p @ 60fps. Same for the CBS affiliate.

My ABC affiliate uses the 1280x720p @ 60fps for their 13-1 HD subchannel and the 640x480p @ 60fps for their other subchannels.

There is a religious station here that uses 640x480p @ 60fps EDTV 4:3 for all four of their subchannels. My STB must supply the pillarboxes for these channels.

For a while our local FOX station was using the 704x480p @ 60fps widescreen format. They eventually switched to the 1280x720p @ 60fps.

The point that should be retained is the 16:9 aspect ratio is not part of the mandate, but once a station chooses the format they are going to use, they do not vary from it. What they do is convert the original programming to fit the format they have chosen.

Most of the programming will be sent out in the 16:9 format. It will be unusual for a station to adopt any of the 4:3 formats as their standard. The exception could be independants that feel they will only be offering 4:3 SD material or secondary channels for weather, etc and cable channels/networks. Now given that the stations will choose one of the 16:9 formats for their HD subchannel, what you will get is a mix of full screen, pillarbox and letterbox video.

The commercials you refered to are shot in 16:9 with the move to 16:9 HDTV being the norm in mind. Most of the time these commercials will be shown with both pillarbox and letterbox so we end up with black bars all the way around. This is because right now when the networks switch to commercials they use the 4:3 analog feed and merge the image into the 16:9 frame rather than using the commercial in HD and cropping the center of the image for the 4:3. On some occasions we see full screen HD comercials, probably depending on the advertiser's desires and budget.

Now the shows that are shot in 16:9 will be shown full screen. If the producers of the show feel like too much of the image would be lost cropped to 4:3, they will broadcast the show in 4:3 letterboxed. Other shows are shot so that they can be cropped for the 4:3 analog broadcast.