Quote:
Originally Posted by Ed in Tx
I can set my converter box to put out either a letterboxed 16:9 on the 4:3 CRT, or it will overscan the sides to fill the screen vertically. There were a few stations here doing a 16:9 stretch on all their 4:3 stuff but they've stopped doing that for the most part.
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Hi,
This is my first post to audiokarma even though I have followed the threads for years.
I am a broadcast engineer and the issue of SD aspect ratio is coming back to burn broadcasters. I do not like to use the term "anamorphic" in the context of DTV since the ATSC standard originally made provision for 4X3 and 16X9 SD.
The ATSC pixel array for SD is 480 X 704. US SD video has never had square pixels: for 4X3 the pixels are a vertical rectangle and for 16X9 the pixels are a horizontal rectangle. Therefore the difference between SD 4X3 and 16X9 is the way the video is captured and presented in a 480 X704 pixel array.
In transmission almost all American broadcasters set their MPEG2 encoder with the signaling flag set to 4X3. This flag is included in the broadcast video stream and tells the DTV receiver how to properly fill the screen. Hence 4X3 video with the aspect ratio flag set to 4X3 will mean that 4X3 screens will be fully filled and 16X9 screens will be provided with side bars.
If on the other hand a broadcaster decided to broadcast 16X9 SD, they would need to present 16X9 video to their MPEG2 encoder and set the aspect ratio flag to 16X9. The flag would tell 4X3 receivers to either “letterbox” or “center crop” the video (viewer choice) and 16X9 receivers would display full 16X9.
Unfortunately an arbitrary decision was made to limit SD to 4X3 only at the beginning of the DTV conversion. Satellite and Cable digital carriage of broadcaster’s SD has been similarly limited because they followed the broadcaster’s arbitrary decision. However, if a broadcaster decided to send out 16X9 video with the aspect ratio flag properly set, it would not affect cable, satellite or home over-the-air reception because all DTV receiving equipment will automatically properly adapt. There would be no fat or skinny video images.