[FFmpeg-devel] [PATCH v2 2/3] libavcodec: add a new AV_CODEC_EXPORT_DATA_FILM_GRAIN flag and option

[Anton Khirnov]

Quoting Lynne (2020-11-14 15:32:35)
> Nov 14, 2020, 11:23 by anton at khirnov.net:
> 
> > Quoting Lynne (2020-11-12 18:42:22)
> >
> >> This introduces a new field to allow decoders to export their film grain 
> >> parameters.
> >> Will be used by the next patch.
> >>
> >> Patch attached.
> >> From d5d5e1e5f90938ac5cfa462efc13658ab411246b Mon Sep 17 00:00:00 2001
> >> From: Lynne <dev at lynne.ee>
> >> Date: Thu, 12 Nov 2020 17:46:09 +0100
> >> Subject: [PATCH v2 2/3] libavcodec: add a new AV_CODEC_EXPORT_DATA_FILM_GRAIN
> >>  flag and option
> >>
> >> This introduces a new field to allow decoders to export their film grain
> >> parameters.
> >> Will be used by the next patch.
> >> ---
> >>  doc/APIchanges             | 3 +++
> >>  libavcodec/avcodec.h       | 5 +++++
> >>  libavcodec/options_table.h | 1 +
> >>  libavcodec/version.h       | 4 ++--
> >>  4 files changed, 11 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/doc/APIchanges b/doc/APIchanges
> >> index 41248724d9..9d0ddb4ff6 100644
> >> --- a/doc/APIchanges
> >> +++ b/doc/APIchanges
> >> @@ -15,6 +15,9 @@ libavutil:     2017-10-21
> >>  
> >>  API changes, most recent first:
> >>  
> >> +2020-xx-xx - xxxxxxxxxx - lavc 58.113.100 - avcodec.h
> >> +  Adds a new flag AV_CODEC_EXPORT_DATA_FILM_GRAIN for export_side_data.
> >> +
> >>  2020-xx-xx - xxxxxxxxxx - lavu 56.61.100 - film_grain_params.h
> >>  Adds a new API for extracting codec film grain parameters as side data.
> >>  Adds a new AVFrameSideDataType entry AV_FRAME_DATA_FILM_GRAIN_PARAMS for it.
> >> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> >> index 20af3ef00d..5047da0f6a 100644
> >> --- a/libavcodec/avcodec.h
> >> +++ b/libavcodec/avcodec.h
> >> @@ -410,6 +410,11 @@ typedef struct RcOverride{
> >>  * Export the AVVideoEncParams structure through frame side data.
> >>  */
> >>  #define AV_CODEC_EXPORT_DATA_VIDEO_ENC_PARAMS (1 << 2)
> >> +/**
> >> + * Decoding only.
> >> + * Do not apply film grain, export it instead.
> >>
> >
> > Could someone want to both apply AND export it?
> >
> 
> Analyzers. In which case they could use a film grain filter to apply it. But that's a fringe
> use-case for this flag, this mainly targets video players and transcoding, where the
> bandwidth/frames savings can be significant.
> There's a WIP Vulkan filter to apply it, and if there's popular demand, the libdav1d code
> could be ported as a software filter.

Then the documentation should allow for applying and exporting.
Also, this flag is supposed to just trigger exporting some metadata, I
am not very comfortable with it changing decoder output.

What's the current status of film grain across the various sw/hw
decoders we have? IIUC some apply it transparently, some don't?
Should there be a way for the user to check?
And/or a common option for "do not apply/apply (if possible)/auto (apply
if export not requested)"?

-- 
Anton Khirnov