[FFmpeg-devel] [PATCH 1/2 v2] avutil: add a Tile Grid API

[James Almer]

On 1/21/2024 3:27 AM, Anton Khirnov wrote:
> Quoting James Almer (2024-01-20 23:04:06)
>> This includes a struct and helpers. It will be used to support container level
>> cropping and tiled image formats, but should be generic enough for general
>> usage.
>>
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>> Extended to include fields used for cropping. Should make the struct reusable
>> even for non tiled images, e.g. setting both rows and tiles to 1, in which case
>> tile width and height would become analogous to coded_{witdh,height}.
> 
> But why? What does cropping have to do with tiling? What advantage is
> there to handling them in one struct?

The struct does not need to be used for non tiled image scenarios, but 
could if we decide we don't want to add another struct that would only 
contain a subset of the fields present here.

As to why said fields here present here, HEIF may use a clap box to 
define cropping for the final image, not for the tiles. This needs to be 
propagated, and the previous version of this API, which only defined 
cropping from right and bottom edges if output dimensions were smaller 
than the grid (standard case for tiled heif with no clap box), was not 
enough. Hence this change.

I can rename this struct to Image Grid or something else, which might 
make it feel less awkward if we decide to reuse it. We still need to 
propagate container cropping from clap boxes and from Matroska elements 
after all.