[FFmpeg-user] sntsc

[Devin Heitmueller]

Hi Mark,

On Tue, Dec 26, 2023 at 2:58 PM Mark Filipak <markfilipak.imdb at gmail.com> wrote:
> Oops. Sorry. SAR for 16:9 DVD is 32/27. PAR is 3/2.
>
> You brought up 40/33. That's a PAR? A PAR for what?

In this context SAR (Sample Aspect Ratio) and PAR (Pixel Aspect Ratio)
are equivalent.  Unfortunately the use of the term "SAR" is ambiguous
as people sometimes mean "Storage Aspect Ratio" or "Screen Aspect
Ratio".  Using PAR avoids that ambiguity.

I would encourage you to review the following page, which has an
entire section on non-square pixels, as well as common values for NTSC
(which talks about the 10:11 and 40:33 commonly found with encoded
NTSC video):

https://en.wikipedia.org/wiki/Pixel_aspect_ratio#Pixel_aspect_ratios_of_common_video_formats

> And my original question: What is "sntsc"?
>
> ‘ntsc’   720x480
> ‘pal’    720x576
> ‘sntsc’  640x480
> ‘spal’   768x576

While I wouldn't have gone with the nomenclature that ffmpeg uses, it
would appear the intent was for "ntsc" to be 720x480 with a DAR of 4:3
(therefore the PAR is 11:10), and "sntsc" to be 640x480 with a DAR of
4:3 (therefore the PAR is 1:1).

> What ffmpeg is calling 'ntsc' & 'pal' are from film scanners targeting pseudo-NTSC DVDs and
> pseudo-PAL DVDs.
>
> What ffmpeg is calling 'sntsc' & 'spal' don't have any relationship to NTSC and PAL, neither film
> nor broadcast, or to DVDs.
>
> Why ffmpeg has put the letters 'ntsc' and 'pal' into 640x480 and 768x576 is a total mystery to me
> and continues the confusion many people have.
>
> I'm sorry I brought it up. It was the marketing people who labeled DVDs as 'NTSC' or 'PAL'. FFmpeg
> is just propagating that myth. I simply ran across 'sntsc' and asked myself, "What is that?"

Frankly, I think the shortcuts were well-intentioned, but not very
well thought out.  If you know what you are doing I would discourage
you from trying to use them and simply specify the real resolution and
framerate using the fps filter and/or the scale filter as needed.

Devin

-- 
Devin Heitmueller, Senior Software Engineer
LTN Global Communications
o: +1 (301) 363-1001
w: https://ltnglobal.com  e: devin.heitmueller at ltnglobal.com