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

[Andrew Randrianasulu]

пн, 8 янв. 2024 г., 13:42 Terje J. Hanssen <terjejhanssen at gmail.com>:

>
>
> 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. 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?
>


well, this is *very possible* that I mixed them all wrong way!


It really advisable to try and get at least main source code downloaded to
you linux machine,Terje.

Even if build attempt fails out we *eventually* will come to something
working, so it will be easier for you to see how changes affect
display/editing of real media.

>
>
> 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
>
>
>
>
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cinelerra-gg.org/pipermail/cin/attachments/20240108/1d4d3581/attachment.htm>