letterboxing 720×480 for 4:3 NTSC playback

[Randy Mack]

I appreciate the detailed response. That confirms my suspicion. I’m still mystified as to why 720×480 is referred to as 4×3 in violation of math, but it’s good to know that it has no bearing on why the image is being cut off at the sides.

Thanks again,
_R

[Jeff Pulera]

Hi Randy,

As others tried to explain, Pixel Aspect Ratio is the key. NTSC with square pixels would be 640 x 480. DV video uses rectangular pixels with a PAR of 0.9, thus the 720 x 480 image is still a 4:3 aspect ratio when viewed.

You may be aware that HD is 16:9 and uses 1920×1080 square pixels. HDV uses 1440×1080 rectangular pixels, but is still a 16:9 image that fills the screen, because the PAR = 1.333, and 1440 x 1.333 = 1920! To further confuse the issue, DVCPROHD is 1280 x 1080 with a 1.5 PAR, and 1280 x 1.5 = 1920, so HD, HDV and DVCPROHD are ALL 16:9 formats and all fill the same screen real estate in the end, at 16:9, using different pixel shapes and pixel counts.

So draw a box on paper with 4:3 dimensions, then fill it with little squares, 640 x 480 of them. Now take that same box, and draw in 720 x 480 little rectangles (0.9 aspect) and they will also fit the 4:3 box. Starting to make sense?

Jeff Pulera
Safe Harbor Computers

[Bob Bascelli]

As others have said, 4:3 is 1.33:1, 720 x 480 is 1.5:1. Further, 16:9 is 1.77:1. All NTSC DVDs are set to display 720×480 regardless of the source aspect ratio. There’s a flag in the DVD coding that’s set to either 16:9 or 4:3.

Check this solution to the cutoff problem (which I’ve encountered):

If shot in, captured and edited in 4:3 and there is cutoff, the pixel aspect may be incorrect in the conversion from the editor into the file used to create the DVD. The Pixel Ratio should be D1. You might have to play a bit. Try exporting a small section.

Keep ’em flying.