[Cin] SAR, DAR, PAR - oh, my!

[Andrew Randrianasulu]

пн, 8 янв. 2024 г., 01:52 Terje J. Hanssen <terjejhanssen at gmail.com>:

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> Den 07.01.2024 23:35, skrev Andrew Randrianasulu:
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> пн, 8 янв. 2024 г., 01:31 Andrea paz <gamberucci.andrea at gmail.com>:
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>> I don't quite understand how ffmpeg considers the various aspect
>> ratios. However from the site lurkertech you pointed to (and from
>> which I had taken some definitions put in the manual) PAR and SAR are
>> not the same thing: PAR is about pixel shape and size; SAR is about
>> frame shape and size.
>>
>> To change the manual I would like to be sure that ffmpeg really
>> considers PAR=SAR.
>>
>
> lets wait until ffmpeg-users reply to just send email :)
>
>>
> The wikipedia article section "Confusion with display aspect ratio" points
> out:
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> https://en.wikipedia.org/wiki/Pixel_aspect_ratio#Confusion_with_display_aspect_ratio
> Pixel aspect ratio is often confused with different types of image aspect
> ratios; the ratio of the image width and height. Due to non-squareness of
> pixels in Standard-definition TV, there are two types of such aspect
> ratios: *storage aspect ratio* (*SAR*) and *display aspect ratio
> <https://en.wikipedia.org/wiki/Display_aspect_ratio>* (abbreviated *DAR*,
> also known as *image aspect ratio
> <https://en.wikipedia.org/wiki/Image_aspect_ratio>* and *picture aspect
> ratio <https://en.wikipedia.org/wiki/Picture_aspect_ratio>*). Also, *pixel
> aspect ratio* (*PAR*) is also known as *sample aspect ratio* (abbreviated
> *SAR*) in some industrial standards (such as H.264
> <https://en.wikipedia.org/wiki/Advanced_Video_Coding>[2]
> <https://en.wikipedia.org/wiki/Pixel_aspect_ratio#cite_note-2>) and
> output of programs (such as *ffmpeg
> <https://en.wikipedia.org/wiki/Ffmpeg>*[3]
> <https://en.wikipedia.org/wiki/Pixel_aspect_ratio#cite_note-3>). Note the
> reuse of the abbreviations *PAR* and *SAR*. This article uses only the
> terms pixel aspect ratio, display aspect ratio and storage aspect ratio to
> avoid ambiguity.
>
> And in Note 3
> "ffprobe shows PAR as SAR" <https://trac.ffmpeg.org/ticket/1776>.
> ffmpeg.org. Retrieved 2022-06-10.
> https://trac.ffmpeg.org/ticket/1776
>

well, both cingg and ffmpeg can interface with digitizing boards, but after
another pass at reading

https://lurkertech.com/lg/video-systems/#sqnonsq

I hopefully hope that only DEVICE DRIVERS for analog input cards must deal
with picture aspect ratio, as they deal with sampling of analog video.

One can also hope that modern smartphone cameras also follow square pixels
convention, because they typically do not send video over SDI but hand it
into system-on-chip shared memory where encoder/display blocks deal with it
directly.


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