It's not actually a big problem, rather a puzzling behaviour.
A 4:3 NTSC mpeg-2 stream plays at 720x540 resolution on VLC.
The archived resolution is 720x480 and AFAIK on U.S. TV sets it's supposed to be displayed anamorphically at 640x480.
I know that 720x540 is as perfect 4:3 as 640x480 is, and that LED displays can use only square pixels. What puzzles me is:
As I understand it, in 4:3 NTSC pixels are stored in such a ratio that you keep the vertical resolution and - huh - "compress" them horizontally to fit 640.
VLC instead apparently keeps the horizontal 720 and stretches vertically to match 4:3 at 540 (resulting in an "almost PAL" resolution).
Which confuses me: those 720 pixels have the "wrong" (non square, slanted) aspect. So in order to display correctly VLC must first compress horizontally (to 640x480 square pixels) and then upscale both axis to 720x540.
Why is this? And can this behaviour impact on image clarity?
I'm asking because MPEGstreamclip plays that same MPEG at 640x480 and comparing png captures from both players shows a slight difference: VLC's snaps exibit more grain and fuzzier details. Not a big difference, but detectable.
BTW This happens on VLC 2.1.3. I tried the same movie in VLC 0.9.10 and it plays @720x540 but snapshots are saved @640x480 (?!?)
I don't know if this behaviour is OS related, but just for the record:
MacOS 10.6, Language italian (PAL country)