[Matroska-devel] PixelCrop* interaction with resolution changes

Matthew Gregan via Matroska-devel matroska-devel at lists.matroska.org
Tue Mar 15 02:42:15 CET 2016


It's possible (with, for example, VP9) to produce a stream that changes
resolution at keyframes.  It's not clear how this should interact with
PixelCrop* values specified in the header, since they are specified in terms
of the original resolution (via the matching values in PixelWidth/Height).

>From https://matroska.org/technical/specs/notes.html#Cropping:
  PixelXXX (size of the coded image)
  -> PixelCropXXX (size of the image to keep)
  -> DisplayXXX (resized cropped image)

When the resolution changes mid-stream, the "size of the coded image"
changes, which seems like it would invalidate any specified pixel cropping.
Does it make sense to simply ignore the cropping values in this case, or is
some other behaviour desired?

Thanks,
-mjg


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