[FFmpeg-devel] [PATCH 3/4] avformat/mov: add support for reading Mastering Display Metadata Box

[Michael Niedermayer]

On Sat, May 27, 2017 at 01:54:18AM -0300, James Almer wrote:
> On 5/26/2017 8:05 PM, Michael Niedermayer wrote:
> > On Wed, May 17, 2017 at 09:49:40PM -0300, James Almer wrote:
> >> As defined in "VP Codec ISO Media File Format Binding v1.0"
> >> https://github.com/webmproject/vp9-dash/blob/master/VPCodecISOMediaFileFormatBinding.md
> >>
> >> Partially based on Matroska decoder code.
> >>
> >> Signed-off-by: James Almer <jamrial at gmail.com>
> >> ---
> >>  libavformat/isom.h |  2 ++
> >>  libavformat/mov.c  | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 67 insertions(+)
> >>
> >> diff --git a/libavformat/isom.h b/libavformat/isom.h
> >> index d9956cf63a..426f732247 100644
> >> --- a/libavformat/isom.h
> >> +++ b/libavformat/isom.h
> >> @@ -27,6 +27,7 @@
> >>  #include <stddef.h>
> >>  #include <stdint.h>
> >>  
> >> +#include "libavutil/mastering_display_metadata.h"
> >>  #include "libavutil/spherical.h"
> >>  #include "libavutil/stereo3d.h"
> >>  
> >> @@ -194,6 +195,7 @@ typedef struct MOVStreamContext {
> >>      AVStereo3D *stereo3d;
> >>      AVSphericalMapping *spherical;
> >>      size_t spherical_size;
> >> +    AVMasteringDisplayMetadata *mastering;
> >>  
> >>      uint32_t format;
> >>  
> >> diff --git a/libavformat/mov.c b/libavformat/mov.c
> >> index afef53b79a..0b5fd849f3 100644
> >> --- a/libavformat/mov.c
> >> +++ b/libavformat/mov.c
> >> @@ -4612,6 +4612,60 @@ static int mov_read_tmcd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> >>      return 0;
> >>  }
> >>  
> >> +static int mov_read_smdm(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> >> +{
> >> +    MOVStreamContext *sc;
> >> +    const int chroma_den = 50000;
> >> +    const int luma_den = 10000;
> >> +    int version;
> >> +
> >> +    if (c->fc->nb_streams < 1)
> >> +        return AVERROR_INVALIDDATA;
> >> +
> >> +    sc = c->fc->streams[c->fc->nb_streams - 1]->priv_data;
> >> +
> >> +    if (atom.size < 5) {
> >> +        av_log(c->fc, AV_LOG_ERROR, "Empty Mastering Display Metadata box\n");
> >> +        return AVERROR_INVALIDDATA;
> >> +    }
> >> +
> >> +    version = avio_r8(pb);
> >> +    if (version) {
> >> +        av_log(c->fc, AV_LOG_WARNING, "Unsupported Mastering Display Metadata box version %d\n", version);
> >> +        return 0;
> >> +    }
> >> +    avio_skip(pb, 3); /* flags */
> >> +
> >> +    sc->mastering = av_mastering_display_metadata_alloc();
> >> +    if (!sc->mastering)
> >> +        return AVERROR(ENOMEM);
> >> +
> > 
> >> +    sc->mastering->display_primaries[0][0] =
> >> +        av_make_q(lrint(((double)avio_rb16(pb) / (1 << 16)) * chroma_den), chroma_den);
> > 
> > this is not optimal, precission wise
> > av_d2q() should produce closer rationals
> > alternativly av_reduce() can be used directly
> > 
> > but iam not sure why a fixed chroma_den and luma_den is fixed
> > maybe iam missing something
> 
> Does
> 
> for (i = 0; i < 3; i++)
>   for (j = 0; j < 2; j++)
>     av_reduce(&sc->mastering->display_primaries[i][j].num,
>               &sc->mastering->display_primaries[i][j].den,
>               lrint(((double)avio_rb16(pb) / (1 << 16)) * chroma_den),
>               chroma_den, chroma_den);

Why do you use
lrint(((double)avio_rb16(pb) / (1 << 16)) * chroma_den
and
chroma_den

instead of
avio_rb16(pb)
and
1 << 16

?

Is the intend to guess the value prior to muxing instead of using
the value actually stored in the mov file ?


[...]
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