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Old 27 Oct 2003, 07:45 PM   #1
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Lightbulb Aspect Ratio, Borders, Resolution solved!

OK, guys! Solved the problem, thought everybody might like to know the results.

The problem was: take a video file at 640x480 (@1:1 VGA = 4:3 Display), encode it to DVD format (720x480, 3:2 DATA -- 4:3 DISPLAY); If you tell it to keep Aspect Ratio, it shrinks to 704x480. WHY?

The answer is, DVD format LIES when it says 720x480 displays at 4:3. It doesn't. It's wider. 704x480 displays at 4:3 (or 16:9, if you're going widescreen). Why this isn't better documented is beyond me, but I checked it out. I took a perfect circle in a video file, encoded it using 720x480 and 704x480, and literally measured how it displayed on screen with a ruler. 704 made a perfect circle, 720 made a wide oval, albeit very slight (10" x 9-1/2").

So, if you want to encode your own borders to protect against TV overburn, do your calculations on 704x480, NOT 720x480. In other words, take your X resolution (for me, 640), multiply by 480, and divide by 704 -- NOT 720. Voila! 436 is the correct Y resolution to keep A/R and protect against overburn, NOT 426. Hope this helps some people out, it sure was frustrating for me!
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Old 1 Nov 2003, 04:46 AM   #2
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Old 27 Nov 2003, 06:43 AM   #3
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720x480 is not a 4:3 aspect ratio. Neither is 704x480. If you play captured DV movies or DV tapes out to a TV screen you'll notice detail missing on both sides of the picture that ARE NOT missing when played on the computer. The TV output is actually clipped on each side of the frame to 640x480 which is the ~true~ 4:3 aspect of std NTSC TV. Do the math:

horizontal 640/4= 160
vertical 480/3= 160

Or, to put it another way (640/4) = (480/3)

If you do this math on other resolutions, and the quotient for horizontal and vertical isn't identical, then it's NOT 4:3 ratio.
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Old 28 Nov 2003, 02:26 AM   #4
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I've been doing a similar thing when resizing my DivX files to burn to DVD. The easiest way is to simply use VirtualDub to resize the avi using the 'resize', video filter and saving the output as a DivX (2000+kbps) at 720x576 or 720x480 (as you NTSC peeps do). Then simply reencode to MPEG2 with a 16:9 flag. I use cinemacraft for that. Easy!
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