Adding black borders and keeping aspect ratio with mencoder?

[Guado]

Hi, I'm encoding some files to MPEG-2. All of them have a size of 720x480 and a 4:3 Aspect Ratio.
My TV produces overscan and crops about 18 pixels in each side.

I'm adding black borders because some of those videos are hardly subbed and I would lose part of text. My problem is that I don't know how to "mathematically calculate" the size of each border in order to keep 4:3 aspect ratio.
I've tried encoding them with the same borders in each side, or adding them like "1.333 x 1". So for example, 18 in right and left sides and 24 in top and bottom. But when I take some screenshots and crop those borders, the image is stretched compared to the original one.

Is there any accurate way to know how many pixels each border must have without stretching image?


Thanks in advance.

[sanlyn]

Most TV's made today have overscan adjustments. Is yours a crt?

[Guado]

Most TV's made today have overscan adjustments. Is yours a crt?

Yes, it's a Trinitron.

[sanlyn]

Whether you modify the borders or not, your output frame size for SD DVD has to be 720x480. You would have to shrink your existing frames porportionally so that you can add 18 pixels to each side. How you'd do that in your software I wouldn't know. Depends on what you're using. But you can expect a quality loss from resizing.

720x480 by size is a 1.5:1 ratio. So your video would shrink to 702x468, then add 18 pix to the sides and 12 to top and bottom to get 720x480. However, whether or not your software simply "fgags" your video for that output is questionable. You would have to "phyiscally" add pixels and make it an integral part of the video. I don't think that can be done without re-encoding.

Any ideas out there? Can't be that impossible. I'm sure members here do this frequently.

[manono]

FitCD can give you the information you need to resize it and add black all around. In the picture below (which is probably what you'll want to use), setting it for 2 blocks resizes it to 672x448 and adds 24 pixels to both sides and 16 both above and below to fill it out to 720x480 and keep the aspect ratio.

[sanlyn]

Yep, just as I found FitCD, manono was already on the case. Thanks for that info. I just got a copy for myself.

[Guado]

Thanks a lot!
It was exactly what I was asking for.

After making some tests with those settings, I could verify that the resulting image was not stretched at all.

Really useful program FitCD.