[FFmpeg-devel] [PATCH] libavutil: add clean aperture (CLAP) side data.

[Tobias Rapp]

On 30.05.2020 12:41, Kieran O Leary wrote:
> Hi,
> 
> On Fri 29 May 2020, 22:47 Neil Birkbeck, <neil.birkbeck at gmail.com> wrote:
> 
>> [...]
>> I've changed the side data to be PixelCrop (instead of CleanAperture) given
>> the intent to reuse as cropping elsewhere.
>> -For now, I've kept the rational representation--although CLAP seems to be
>> the only required case of it. Maybe Kieran could comment on the requirement
>> of having maintaining the rationals for CLAP (only works on mov to mov
>> transmuxing).
>>
> I'm no expert, but I think a lot of this just comes from video standards
> that stipulate those rational numbers? I've cc'd tobias Rapp and Christoph
> Gerstbauer of NOA just to bring this to their attention, as I'm pretty sure
> that they use cropping values in AVI, so perhaps all of this could be
> useful to them in some way.
> 

Hi Kieran,

when digitizing SD video carriers we indeed store some offset 
information in case VBI is preverved (i.e. PAL 720x608). But these 
offset values are currently not stored in the AVI container itself. The 
OpenDML "vprp" chunk defines some offset values but for the purpose of 
compressed image data where the codec implies some multiple-of-N 
height/width dimension on the data. So it did not seem to match our 
use-case.

Besides AVI and the mentioned MKV and MOV formats I remember some 
display offset/cropping information being stored in MXF with the Display 
X/Y-Offset values.

Regardless whether the frame crop/offset values are stored as frame 
fields or side data: how would this information be affected by filters 
like "crop" or "scale"?

Regards,
Tobias