Are FitCD aspect ratios wrong?

[r6d2]

Hi. shh based its excellent FitCD tool on what he learnt on this table:

http://www.uwasa.fi/~f76998/video/conversion/#conversion_table

I revised the table and cannot but conclude the logic is OK. However, in practice sometimes things are different from what they look in theory.

I encoded a short clip using the 7 typical resolutions (or frame sizes, more correctly) of FitCD: VCD, CVD, SVCD, DVD3/4S, DVD3/4F, XVCD, DVD.

I used exactly the script FitCD suggests to preserve aspect ratio, this is, Crop(8,0,-8,0) for 704-based frame sizes (VCD, CVD, DVD3/4S, XVCD, and then AddBorders(2,0,2,0) for the DVD3/4F case. Nothing for SVCD and DVD.

Done this, I supposed, if I played the 7 clips in order of lower to higher frame size, I would see the exact same image in all of them, just with higher sharpness.

Interestingly enough, they wouldn't. They actually change their width considerably. Specially DVD3/4S, which would look a lot better without the Crop command FitCD suggests.

If you would like to try for yourself, please download the image file from this post's links:

http://forum.doom9.org/showthread.php?s=&postid=378891#post378891

Can anyone explain why this happens? Is FitCD wrong at attempting to preserve aspect ratios?

[r6d2]

OK, here is what I have found out after some email ping-pong with shh:

1. DVD 3/4S appears not to be a 704-based frame size after all.

2. If you player supports SVCD & DVD 3/4 frame sizes, it is likely to support any width in the 480-720 range. All these frame sizes are scaled using the same simple proportion rule (except of course 704 itself).

3. Widths greater than your TV horizontal resolution are likely not to give you better image :(.

This last point means that if your TV is a regular 427 "pixels" wide, your SVCDs will look as well as the original DVDs and you may not be able to tell the difference!

My findings are for NTSC, shh is testing on PAL land.