[FFmpeg-user] Chroma subsampling formats

[Mark Filipak]

On 15/07/2025 16.04, Paul B Mahol wrote:
> On Tue, Jul 15, 2025 at 7:57 PM Mark Filipak <markfilipak.imdb at gmail.com>
> wrote:
> 
>> On 15/07/2025 15.40, Paul B Mahol wrote:
>>> On Tue, Jul 15, 2025 at 7:34 PM Mark Filipak <markfilipak.imdb at gmail.com
>>>
>>> wrote:
>>
>>>> KEY:
>>>> ¤ —— Element exists in the field and is sampled
>>>> • —— Element exists in the field but is not sampled
>>>>   —— (blank) Element doesn't exist in the field
>>>> >>>>            Y element, pixels 0..3
>>>>           /    Cb element, pixels 0..3
>>>>          /    /    Cr element, pixels 0..3
>>>>         /    /    /
>>>> 4:4:1  ¤¤¤¤ ¤¤¤¤ ¤¤¤¤ —— lines in field 0
>>>>        ¤¤¤¤ ¤••• ¤••• —— lines in field 1
>>>>
>>>> 4:2:1  ¤¤¤¤ ¤•¤• ¤•¤•
>>>>        ¤¤¤¤ ¤••• ¤•••
>>
>> Well, Paul, you're the expert. Are those two correct? If they are, then I'm right about
>> how the tokens work and the folks at wikipedia are wrong. I don't care whether the
>> wikipedia folks are right or wrong because I don't pay wikipedia any mind because I
>> think wikipedia is a train wreck. I want to be right because I want to be knowledgeable
>> so I can help myself and so I can help other people.

Not that you were on any hook, Paul, but I'm letting you off the hook. Of course you don't know 
whether my 4:4:1 and-or 4:2:1 are correct because you don't have any experience with such odd 
subsample formats. But I think I know how to get an answer.

If you or anyone has a pro authoring tool and can create a video, any video, maybe 2 or 3 seconds, 
with 4:2:1 subsampling, I'll examine it and find out what's what.

It's me versus wikipedia. I think I'm right about how to interpret subsample format. There's two 
reasons why I think I'm right. 1, I have a solution but wikipedia doesn't -- they say "except in 
rare irregular cases like 4:4:1 and 4:2:1, which do not follow this [their] convention". And 2, my 
solution works as well as theirs for the other subsample formats.

So, what do you say? Can you or anyone make such a 2 or 3 second video and send it to me?

--Mark.