Basic letterbox question

[dhsvcs]

I know it's been discussed before, and I searched the forums to find a more detailed explanation. I captured a PowerPoint presentation with camedia at 800 x 600. Brought it down to 600 x 400 letterboxing
it to 720 x 480 with virtual dub. Used ulead dvd workshop and I now have a nice playong dvd that plays on a 4/3 television with very little border. I use the original file for dvd playback on my computer. Why do I have to shrink all the way to 600x400 so I don't loose content on a regular tv screen using a dvd player ?

I tried different sizes ( 630 wide, 660 wide, maintaining corresponding vertical ratio ) and they loose edges of content.

1. Is this much letterboxing required ?
2. Am I doing something wrong ?
3. Why doesn't this happen with purchased dvd's ?..I know the dvd
player adds the black bars automatically, can I make a dvd
that will do the same, playable on both a computer & tv without
seperate recordings ?

[r6d2]

Let me see if I get this straight. Source was 800x600 (4:3 DAR, 1:1 PAR), you resized to 600x400 (1.5 DAR, 1:1 PAR). Then you letterboxed it to 720x480 (NTSC PAR).

I'm not sure but seems to me that you did not keep the original AR. Does the picture look OK or does it look squished vertically or horizontally?

You could resize directly from 800x600 (1:1 PAR) to 720x480 (NTSC PAR). A good resizing tool which will generate the apropriate AviSynth script is FitCD. Select 1:1 PAR on source and NTSC PAR on target. To avoid losing content due to overscan, adjust the Overscan count to 3.

To encode in such a way that it plays correcly without excessive resizing on a 4:3 TV (or PC monitor) or 16:9 TV, select anamorphic aspect on target. If you have questions don't hesitate to ask.

[dhsvcs]

I tried playing back dvd on tv after authoring it on a few programs.
In all cases, the video was oversized and did not fit on screen.
By making the video 600x400 and letterboxing it to 720x480 (at the same time) in virtual dub and saving it as an avi file, I was now able
to burn the avi file as a dvd and play the video successfully on a tv with a dvd player with hardly any bars ( less than 1 percent )showing on any side. Naturally, the same dvd was horrible on a computer dvd playing program,for the letterbox was shown on all sides.

Playing a dvd on tv with the original file written at 720x480 had a very large portion of content off the sreen on all sides, though it played perfectly on power dvd and nero showtime..

Also, I never lost perspective/proportion in the process..
I will try what you suggested, for I will learn how to get the darn process down right...Thank you, dhsvcs