Why do DVDs contain "black" portions that contain no information?

[Shaocaholica]

This is a pretty common thing. Why do DVDs contain so much unused space in its alloted frame and thus every time we encode these are better off cropped out. Why don't the movie studios use the entire frame or at least keep the wasted space to a minimum? Is this true also for BR and HD-DVD movies?

[M_Knox]

Well, that's because TV crops video to some extent. You may wish to try it yourself - do author a DVD that contains a fullframe picture (no borders), display it on your TV and see how much of the picture is gone.

[CWR03]

Why do DVDs contain so much unused space in its alloted frame and thus every time we encode these are better off cropped out
For one thing, leaving the black borders intact when encoding to MPEG-4 has little effect on the size the new file, since the large still areas require practically no bitrate to encode. For another, studios aren't too concerned whether or not border cropping is inconvenient to users backing up DVDs in another format.

[Shaocaholica]

For one thing, leaving the black borders intact when encoding to MPEG-4 has little effect on the size the new file, since the large still areas require practically no bitrate to encode. For another, studios aren't too concerned whether or not border cropping is inconvenient to users backing up DVDs in another format.

Yes but its still a waste of bandwidth on the DVD and if they utilized the full frame, they can squeeze more resolution into the final image displayed. The whole overscanning issue seems so ridiculous. If every DVD is missing at least 20 pixels on the top and bottom of the frame, why not put that into the DVD standard and have the player put that empty overscan space there instead of actually encoding it into the frame?

[LoRd_MuldeR]

TV signals actually must contain the black borders for historical reasons! It's called "Schwarzschulter" (German), the English word is "black burst" I think. CRT displays depend on the black area at the end of the line! While the black area is transmitted, there are no information, so the CRT screen can use this time to move the electron beam from the end of the current line to the beginning of the next line. If there was no black area, there would be no time for the CRT to move it's electron beam to the next line. Also the black area is used to re-calibrate the black level of the signal...

BTW: It's not the black area itself that eats additional bitrate, it's the change-over between the "visible" area and the black area that does...