Capital Currents - 21 x 9 Challenges
One thing is clear: Whatever decisions are made, there will probably be changes to numerous industry standards.
Do you watch a lot of Blu-ray movies? Then maybe a 21 x 9 TV display is right for you. Why? Because one of the most common aspect ratios for theater display of movies is 2.39:1, which is close to 21 x 9. Those movies are shot with a wide aspect ratio that tries to take advantage of the wide field of view of human eyesight. A number of TV manufacturers have announced plans to sell TVs with a 21 x 9 display format. But how would cable and TV transmissions accommodate 21 x 9 displays? And what standards would need to be modified? Folks are starting to give these questions some thought.
Most digital TVs now on the market have a pixel display format of 1920 x 1080, which is an aspect ratio of 16 x 9 or 1.78:1. The new widescreen TVs from Vizio and Philips have a pixel display format of 2560 x 1080 – an aspect ratio of 21.3 x 9 or 2.37:1. Not exactly 2.39:1, but close enough.
You might remember in the early days of digital TV broadcasting, many broadcasters were still using 4 x 3 cameras. But they were transmitting a 16 x 9 signal, and to do that, they put black “pillar bars” on the right and left sides of the signals they were sending. So if you happened to have a 16 x 9 display, you saw exactly what was sent: a 4 x 3 picture with black pillar bars. But in those early days, many of the HDTV receivers had 4 x 3 CRT displays. They displayed 16 x 9 pictures with a black bar (or a “letterbox bar”) at the top and bottom. So if you had a digital TV with a 4 x 3 display, what you saw was a 4 x 3 picture framed by black bars on all four sides (sometimes called a “postage stamp image”).
In order to provide future TV receivers with information about these black bars so that the picture could be automatically “zoomed” by the TV to cut off the bars and show the whole display, the industry developed standards for Active Format Description (AFD) and bar data. The AFD and bar data specifications now appear in numerous industry standards. They originated in the European DVB digital television standard (ETSI TS 101 154, which can be freely downloaded). They became part of the ATSC A/53 digital television standard, which specifies how the information is carried within the MPEG-2 video stream delivered by U.S. broadcasters and cable program services. SCTE 128 specifies how AFD and bar data are carried in AVC-coded video. For carrying AFD and bar data across baseband interfaces, CEA-861 covers HDMI, and CEA-805 covers wideband component analog signals. And, finally, bulletin CEA-CEB-16 gives recommendations for the receiving devices that create and display the pictures.
The AFD data specifies the format of the active picture. AFD is most often used to indicate when 16 x 9 video or 14 x 9 video is to be displayed letterboxed within a 4 x 3 frame, or when 4 x 3 video is to be displayed “pillarboxed” in a 16 x 9 frame.
Bar data gives precise sizes and locations for letterbox or pillar bars. Bar data was expected to be used as a supplement to AFD to more precisely signal video formats that are neither 4 x 3 nor 16 x 9. But I understand that few broadcasters and cable operators actually deliver bar data.
The AFD and bar data specifications were developed in a world that contained only 4 x 3 and 16 x 9 displays. There was no thought given to 21 x 9 displays. But some standards bodies are now starting to look at whether to add explicit support for 21 x 9 (2.39:1) movies and 21 x 9 (2560 x 1080) displays in their standards. For example, CEA has begun looking at adding the 21 x 9 format to the CEA-861 HDMI interface standard.
It’s hard to know where this is heading. Will broadcasters ever transmit 2560 x 1080 programs? Probably not. For one thing, with MPEG-2 video coding, the data rate would not fit into a broadcaster’s 19 Mbps data stream.
But maybe there will be 2560 x 1080 cable channels. We now have a few cable channels that are delivering 3-D video, which can only be displayed by 3-Dcapable receivers. So maybe we will have 21 x 9 movie channels, delivering only 21 x 9 programs that can only be displayed on 21 x 9 receivers. And there are already prerecorded Blu-ray discs that can deliver 2560 x 1080 movies.
Will there be a standard way to tell 16 x 9 receivers to add letterbox bars to 2560 x 1080 movies? Or will 21 x 9 movies, in the future, be sent letterboxed within a 1920 x 1080 (16 x 9) frame like they are today, but with standard instructions for 21 x 9 displays to delete the letterbox bars? Does the HDMI interface support the higher data rate of a 2560 x 1080 picture? What to do about movies that are even wider than 21 x 9?
One thing is clear: Whatever decisions are made, there will probably be changes to numerous industry standards to accommodate 21 x 9 movies and displays.
E-Mail: firstname.lastname@example.org