On Tue 26 Dec 2023 at 22:53, Mark Filipak <[email protected]> wrote:
> On 12/26/23 15:30, Devin Heitmueller wrote: > > Hi Mark, > > > > On Tue, Dec 26, 2023 at 2:58 PM Mark Filipak <[email protected]> > 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 _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
