[FFmpeg-devel] [PATCH 1/3] lavu: Add AVSphericalMapping type and frame side data

Michael Niedermayer michael at niedermayer.cc
Tue Nov 15 03:55:00 EET 2016

On Mon, Nov 14, 2016 at 04:55:36PM -0500, Vittorio Giovara wrote:
> On Sun, Nov 13, 2016 at 11:57 AM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> > On Sun, Nov 13, 2016 at 10:18:18AM +0100, Michael Niedermayer wrote:
> >> On Sat, Nov 12, 2016 at 10:05:22PM -0500, Vittorio Giovara wrote:
> >> [...]
> >> > So I really do not see a use case for using int64 here.
> >>
> >> then you can use int32, less than int32 is too little if for example
> >> you wnat the precission to be sufficient to know where a tele lens
> >> points with pixel precission and have a bit precission headroom
> Hi Michael, thanks for keeping me in CC.
> I understand the problem, but this is a solution for a issue that is
> non-existent.

The problem of difficut to test code is real and existing in general.
Encoders&muxers using floats/doubles can not be tested as completely as
Encoders&muxers not using floats unless they by chance give binary
identical results on all platforms.

Muxers&encoders would use/write the rotation side data

Similarly ffprobe would at some point print this data, the text
printout of doubles has a good chance to not match exactly between

> There is no application or usecase for "pixel perfect"
> precision, the rendering of a spherical video will distort the video
> surface in order to map the flat surface to a sphere, and it is
> impossible to predict where this operation will move pixels to. I
> believe this is why this specification describes the initial
> orientation as rotation degrees rather than pixel offsets.

I referred to pixels only to show that 32bit floats are insufficiently
precisse in some cases.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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