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

[Terje J. Hanssen]

Den 08.01.2024 01:39, skrev Andrew Randrianasulu:
>
>
> пн, 8 янв. 2024 г., 01:52 Terje J. Hanssen <terjejhanssen at gmail.com>:
>
>
>
>     Den 07.01.2024 23:35, skrev Andrew Randrianasulu:
>>
>>
>>     пн, 8 янв. 2024 г., 01:31 Andrea paz <gamberucci.andrea at gmail.com>:
>>
>>         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:
>     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 <http://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.
>
Hm, yet another definition; "Picture Aspect Ratio" used.


However, the CinGG manual seemingly uses this Pixel-Display-Storage 
Aspect Ratio definitions:
https://cinelerra-gg.org/download/CinelerraGG_Manual/Temporary_Track_Output_Size.html#2525

In Settings → Format there is the additional possibility to vary the 
shape of the pixels from 1:1 (square) to handle anamorphic formats. In 
such cases we use:

/PAR/ = DAR/SAR

Is it correct that Canvas size "W Ratio" and "H Ratio" define PAR, while 
"Aspect Ratio" defines DAR in the Settings > Format widget?

But there is something confusing I don't understand (possibly wrong) 
with the Presets values as far as I can see:

  * Preset 1080i/25 set:             Canvas size Width=1920,
    Height=1080, W Ratio=1.3333, H Ratio=1.0000 and Aspect
    ratio=16.0000:9.0000
  * Preset HDV 1080i/25 set:    Canvas size Width=1440, Height=1080, W
    Ratio=1.0000, H Ratio=1.0000 and Aspect ratio=16.0000:9.0000

The first is obviously  FHD w/DAR=16:9 out of the frame size 1920x1080. 
If so, shouldn't PAR be 1:1, that is W Ratio=1.000 and H Ratio=1.000?
The second HDV w/DAR=16:9 (anamorphic squeezed), should seemingly 
instead have PAR 4:3, that is W Ratio=1.3333, H Ratio=1.0000?

Else the PAL SD-DV(D) is seemingly ok

  * Preset PAL 576i -DV(D) set: Canvas size Width= 720, Height=576, W
    Ratio=0.5000, H Ratio=0.5333 and Aspect ratio=4.0000:3.0000





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