On 11/17/2020 8:15 AM, Lynne wrote:
Nov 17, 2020, 10:58 by an...@khirnov.net:
Quoting Lynne (2020-11-17 00:21:43)
Nov 16, 2020, 15:56 by ffm...@haasn.xyz:
In terms of an API user needing this functionality, the way I see it
working is that presence of the side-data will imply that it still needs
to be applied, with the side data being removed the moment grain
actually is applied. So that means that decoders applying film grain
must never export this side data, and decoders not applying film grain
must always export this side data.
A decoder both applying grain and exporting the side data is
nonsensical, and would only result in double-grain-application. In terms
of the capability checking, I don't need you to tell me whether or not
the decoder can apply/export side data or not, rather, I need to tell
*you* whether or not I can apply film grain myself. This is what I
understand AV_CODEC_EXPORT_DATA_FILM_GRAIN to be. Whether or not it's
actually exported when that flag is present is irrelevant to me, all I'm
trying to do is signaling that I'd prefer film grain to be exported
rather than applied.
Yup, that's my idea of how this should work as well.
Maybe even analyzers should want to skip applying film grain in a majority
of cases or apply it independently. So I still think of having an export
flag control the decoder behavior is acceptable in this case.
It's not about majority vs. minority, the question is
"is there EVER a valid reason to apply AND export?"
If the answer is yes, then there needs to be a way to do that. The flag
you're proposing explicitly says you can do either one or the other, but
never both.
That's a kinda black and white view. We have both APIs that don't allow very
common cases to be handled and are creating us problems and we have APIs
which allow for completely unreasonable things to happen and are creating
us problems as well.
I don't think there's a reasonable non-contrived case in which you'd want to
both export and apply film grain. But I also didn't think there's a reasonable
case to ever need to chain demuxers and decoders.
Just to check, The existence of this flag as it was defined implies
there should not be an "apply grain" avoption in decoders that can
export such params as side data, to avoid conflicts, right? The flag
alone is meant to control if film grain is applied, or exported.
Now, what about decoders that can't export film grain params as side
data? Take for example QSV, which may not allow it. Should such decoders
offer an avoption to apply film grain or not? For those, the export flag
can't be used to disable applying film grain because it can't also
fulfill the "export" part of its purpose.
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