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

Neil Birkbeck neil.birkbeck at gmail.com
Mon Feb 1 21:11:10 CET 2016


Please see updated patch.

On Mon, Jan 25, 2016 at 11:39 PM, Neil Birkbeck <neil.birkbeck at gmail.com> wrote:
> I guess png is another example; 100000 is the denominator for the 32-bit
> integer:
> https://github.com/FFmpeg/FFmpeg/blob/b58cfa616c169c90166938608e7135cdab5820e0/libavcodec/pngenc.c#L290
>
> In the standards, the primaries and white point coords are usually only
> referenced in 2-4 significant figures (ISO/IEC 23001-8:2013(E) has them all
> in one doc). The display primaries can be different from these, but I don't
> think you'd see them measured with any more precision (more precision is
> unlikely to matter for this metadata anyway).
>
> It seems that most are in favor of AVRational, so I'll change the avutil
> struct float internal fields to rational.
>
>
>
>
>
> On Mon, Jan 25, 2016 at 1:43 PM, Hendrik Leppkes <h.leppkes at gmail.com>
> wrote:
>>
>> 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
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>
>
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