[FFmpeg-user] sntsc

[Kieran O Leary]

On Tue 26 Dec 2023 at 22:53, Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 12/26/23 15:30, Devin Heitmueller wrote:
> > 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.
>
> On what planet are SAR & PAR 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.
>
> Yes, people misuse terms, mainly because the terms are not defined. The
> H.262 definitions have no
> relevance in the real world.
>
> "3.114 sample aspect ratio (SAR): This specifies the relative distance
> between samples. It is
> defined (for the purposes of ITU-T Rec. H.262 | ISO/IEC 13818-2), as the
> vertical displacement of
> the lines of luminance samples in a frame divided by the horizontal
> displacement of the luminance
> samples. Thus, its units are (metres per line) ÷ (metres per sample)."
>
> That definition applies solely to flying-spot scanners -- note that it is
> vertical (line-to-line)
> spacing divided by horizontal (pixel-to-pixel) spacing. To everyone else,
> H/W is upside down.
> H.262 then goes on to define a DAR that's upside down:
>
> "3.44 display aspect ratio: The ratio height/width (in spatial measurement
> units such as
> centimeters) of the intended display."
>
> H.262 avoids "PAR" and "pixel aspect" altogether. There's not a mention.
> That was intentional. So,
> to the ITU (and presumably to MPEG), PAR doesn't exist. Some call it
> 'pixel aspect' and some call it
> 'picture aspect'. Curiously, the ITU (and presumably to MPEG) define a
> 'picture', thusly:
>
> "3.97 picture: Source, coded or reconstructed image data. A source or
> reconstructed picture consists
> of three rectangular matrices of 8-bit numbers representing the luminance
> and two chrominance
> signals. A 'coded picture' is defined in 3.21 of ITU-T Rec. H.262 |
> ISO/IEC 13818-2. For progressive
> video, a picture is identical to a frame, while for interlaced video, a
> picture can refer to a
> frame, or the top field or the bottom field of the frame depending on the
> context."
>
> So, to the ITU (and presumably to MPEG) data is a picture. Good grief...
>
> > 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):
>
> 704x480 is illegal for DVD. It either gets padded out to 720x480, or
> cropped to 704x469, then scaled
> to 720x480, or some combination of the two methods. But 704x420 is not
> legal for DVDs -- there's no
> such aspect choice in PES headers.
>
> >
> https://en.wikipedia.org/wiki/Pixel_aspect_ratio#Pixel_aspect_ratios_of_common_video_formats
>
> Oh, no! Mister Billipedia!  Hahahaha... (where people who are as ill
> informed as you are, get to
> pontificate)


I think you must have misread the tone of Devin’s email, and I would hardly
call him ill informed. His post was constructive and your language will
only derail threads like this.

Please read the code of conduct
https://ffmpeg.org/community.html#Code-of-Conduct-1

Best,

Kieran