Re: [FFmpeg-devel] [PATCH] [MXF] - Set aspect ratio for jpeg2000 images

["Tomas Härdin" <git@haerdin.se>]

tis 2024-01-30 klockan 10:47 +0100 skrev Tomas Härdin:
> fre 2024-01-26 klockan 10:12 -0800 skrev Pierre-Anthony Lemieux:
> > On Fri, Jan 26, 2024 at 10:02 AM Cédric Le Barz
> > <clebarz@ektacom.com>
> > wrote:
> > > 
> > > Set aspect ratio for jpeg2000 images.
> > 
> > "The image area on the reference grid is defined by its upper left
> > hand reference grid point at location (XOsiz, YOsiz), and its lower
> > right hand reference grid point at location (Xsiz – 1, Ysiz – 1)"
> > (15444-1, 8.2)
> > 
> > AFAIK setting the MXF aspect ratio item to the ratio of the image
> > pixel dimensions only works if (a) the pixel aspect ratio is 1 and
> > (b)
> > the video is not interlaced -- see 6.2.1.2 and Annex H at
> > https://pub.smpte.org/doc/st2067-21/20221124-pub/.
> 
> You also need to know the display rectangle. If for example VBI lines
> are present then these might also need be cropped, in addition to the
> cropping done at the J2K level. Sometimes container and essence
> disagree on what SAR is, which affects the DAR. Which value is the
> correct one typically depends on business logic
> 
> A demuxer is the wrong place to put logic like this

Wups, missed that this is a muxer patch, not a demuxer one.

Anyway, this patch is very wrong. DAR is a container level thing. We
shouldn't take it from the essence unless there is overwhelming reason
to do so. My point about VBI still stands, in modified form: if VBI
lines are present then this patch would write a bogus DAR

Much of the logic currently in mxfenc.c should probably live somewhere
higher up since MOV also supports some of these things

/Tomas
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