[FFmpeg-devel] [PATCH 1/3] spherical: Add tiled equirectangular type and projection-specific properties

Aaron Colwell acolwell at google.com
Thu Feb 16 22:41:13 EET 2017

On Thu, Feb 16, 2017 at 11:09 AM Vittorio Giovara <
vittorio.giovara at gmail.com> wrote:

> On Wed, Feb 15, 2017 at 2:54 PM, Aaron Colwell <acolwell at google.com>
> wrote:
> > Hi Vittorio,
> >
> > This may not be a blocker for this patch, but one issue with converting
> the
> > bounds to pixels like you do here is that resizing a video could result
> in
> > incorrect metadata being generated when muxing. If you keep the bounds in
> > the 0.0-1.0 fixed point space this problem doesn't happen since it is a
> > resolution independent representation. If you still want to use pixels
> here
> > then the resizing filter will need to become aware of AVSphericalMapping
> and
> > adjust it accordingly. I think cubemap padding in pixels may have a
> similar
> > issue. This is no way intended to be a blocking comment. It is just
> meant to
> > raise awareness on something you might not have considered.
> Hi Aaron,
> this is an interesting point, but leaves up open questions. Do you
> foresee actual cases in which this is going to be a problem? It's not
> the first time we have fixed point fields exported, but it's also true
> that the conversion from a 0.32 system is not very common and could
> leave users puzzled. Regarding padding, is the specification going to
> be updated to fix this potential issue?
> Thank you
> --
> Vittorio

Hi Vittorio,

After sleeping on this, I think what you have will be fine. Resizing a
cubemap w/ padding is just going to have to be handled in a special way
because fractional pixel padding isn't going to work right on the GPU. You
really only want to waste a few pixels on padding, not a constant fraction
of the whole frame. Given that we have to handle cubemaps in a special way
for resizing, then my thoughts about resizing equirect aren't really a big
deal. I don't expect any spec changes will be needed for this.

I suppose this just a long way of saying "we will still need a followup for
resizing spherical videos properly, but this patch LGTM."

Thanks again for working on this.

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