Re: [FFmpeg-devel] [PATCH v3 10/12] avcodec/libsvtav1: add support for writing out CLL and MDCV

From: "Jan Ekström" <jeebjp@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v3 10/12] avcodec/libsvtav1: add support for writing out CLL and MDCV
Date: Tue, 22 Aug 2023 00:38:02 +0300
Message-ID: <CAEu79SZJ8pEC8ApB8+nm85Mn5n0wctKRpsb9hCvFtTM+7adzow@mail.gmail.com> (raw)
In-Reply-To: <AS8P250MB07445CBAF92366827D1306978F19A@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM>

On Sun, Aug 20, 2023 at 10:10 AM Andreas Rheinhardt
<andreas.rheinhardt@outlook.com> wrote:
>
> Jan Ekström:
> > These two were added in 28e23d7f348c78d49a726c7469f9d4e38edec341
> > and 3558c1f2e97455e0b89edef31b9a72ab7fa30550 for version 0.9.0 of
> > SVT-AV1, which is also our minimum requirement right now.
> >
> > In other words, no additional version limiting conditions seem
> > to be required.
> >
> > Additionally, add a FATE test which verifies that pass-through of
> > the MDCV/CLL side data is working during encoding.
> > ---
> >  libavcodec/libsvtav1.c         | 70 ++++++++++++++++++++++++++++++++++
> >  tests/fate/enc_external.mak    |  5 +++
> >  tests/ref/fate/libsvtav1-hdr10 | 14 +++++++
> >  3 files changed, 89 insertions(+)
> >  create mode 100644 tests/ref/fate/libsvtav1-hdr10
> >
> > diff --git a/libavcodec/libsvtav1.c b/libavcodec/libsvtav1.c
> > index f2b73361d8..d4f9fa14ba 100644
> > --- a/libavcodec/libsvtav1.c
> > +++ b/libavcodec/libsvtav1.c
> > @@ -24,9 +24,11 @@
> >  #include <EbSvtAv1ErrorCodes.h>
> >  #include <EbSvtAv1Enc.h>
> >
> > +#include "libavutil/bswap.h"
> >  #include "libavutil/common.h"
> >  #include "libavutil/frame.h"
> >  #include "libavutil/imgutils.h"
> > +#include "libavutil/mastering_display_metadata.h"
> >  #include "libavutil/opt.h"
> >  #include "libavutil/pixdesc.h"
> >  #include "libavutil/avassert.h"
> > @@ -146,6 +148,72 @@ static int alloc_buffer(EbSvtAv1EncConfiguration *config, SvtContext *svt_enc)
> >
> >  }
> >
> > +static void handle_mdcv(struct EbSvtAv1MasteringDisplayInfo *dst,
> > +                        const AVMasteringDisplayMetadata *mdcv)
> > +{
> > +    struct EbSvtAv1ChromaPoints *points[] = {
> > +        &dst->r,
> > +        &dst->g,
> > +        &dst->b,
> > +    };
> > +
> > +    if (!mdcv->has_primaries)
> > +        goto skip_primaries;
> > +
> > +    for (int i = 0; i < 3; i++) {
> > +        struct EbSvtAv1ChromaPoints *dst = points[i];
> > +        const  AVRational           *src = mdcv->display_primaries[i];
> > +
> > +        dst->x =
> > +            AV_BSWAP16C(av_rescale_q(1, src[0],
> > +                                     (AVRational){ 1, (1 << 16) }));
>
> Can you explain what's the matter with the AV_BSWAP16C here? And if I am
> not mistaken, then the av_rescale_q() above is equivalent to src[0] * (1
> << 16) (if we had multiplications of AVRationals by integers).

It's basically a way that I got the big-endian values written out to
the uint16_t. Same goes for the uint32_t values and AV_BSWAP32C. Not
sure if there is a better macro for handling this on both BE and LE.

SVT-AV1 seems to just write these values into the bit stream as-is and
the interface seems to be defined around that (f.ex. in the string
based interface `x << 8 | x >> 8` is always done to the parsed value).

https://gitlab.com/AOMediaCodec/SVT-AV1/-/blob/7233e7ead5fe8a0f1dc33b91aba0c5a24cb9f673/Source/Lib/Encoder/Codec/EbEntropyCoding.c#L3626-3637

Jan
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