[FFmpeg-devel] [PATCH] lavc/hevc Parse SEI_TYPE_MASTERING_DISPLAY_INFO and propagate contents into the AVMasteringDisplayMetadata side data.

[Hendrik Leppkes]

On Mon, Jan 25, 2016 at 10:37 PM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Fri, Jan 22, 2016 at 02:54:21PM -0800, Neil Birkbeck wrote:
>> Hmm. I don't have a good idea of how likely it is for this conversion to
>> float (by dividing a constant) to not be bit-exact on different
>> architectures (compilers?) when there should not be any other math
>> transforming the metadata (other than the conversion back to the integer
>> coding for cases like hevc, which for a given architecture is possible
>> without loss). The fact that this could happen at all does make it annoying
>> in terms of bit-exact test expectations across arch, and this is the main
>> concern, right? (for this type of metadata, it is really a hint to
>> TVs/algorithms, and some will ignore it altogether)
>
> bitexactness is one concern, also theres the issue with what is ideally
> correct.
> that is what are the ideal values dictated by various standards
> that hardware (cammeras, ...) aim at ?
> are these rational or float or what can represent them better ?
>

Both HEVC and the HDMI Info Frames use fixed-point integers (the same
scales too, apparently), I do not know of the formats anything else
uses.
Maybe we should be using AVRationals?

I would argue that MKV storing floats is a terrible idea, and someone
should bonk them over the head and store fixed point as well.

- Hendrik