[FFmpeg-devel] [PATCH] lavc/x265: set preferred_transfer_characteristics for HLG

[Zhong Li]

James Almer <jamrial at gmail.com> 于2019年12月13日周五 上午12:14写道：
>
> On 12/4/2019 11:24 AM, Zhong Li wrote:
> > "HEVC HDR UHDTV Bitstreams using HLG10 shall also contain the
> > alternative_transfer_characteristics SEI message. The
> > alternative_transfer_characteristics SEI message shall be inserted on
> > the HEVC DVB_RAP, and preferred_transfer_characteristics shall be set
> > equal to "18", indicating Recommendation ITU-R BT. 2100 [45] HLG
> > system."
> >
> > Signed-off-by: Zhong Li <zhongli_dev at 126.com>
> > ---
> >  libavcodec/libx265.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/libavcodec/libx265.c b/libavcodec/libx265.c
> > index 4e75077..963c28f 100644
> > --- a/libavcodec/libx265.c
> > +++ b/libavcodec/libx265.c
> > @@ -159,6 +159,10 @@ static av_cold int libx265_encode_init(AVCodecContext *avctx)
> >          // x265 validates the parameters internally
> >          ctx->params->vui.colorPrimaries          = avctx->color_primaries;
> >          ctx->params->vui.transferCharacteristics = avctx->color_trc;
> > +#if X265_BUILD >= 159
> > +        if (avctx->color_trc == AVCOL_TRC_ARIB_STD_B67)
> > +            ctx->params->preferredTransferCharacteristics = ctx->params->vui.transferCharacteristics;
> > +#endif
>
> isn't the point of preferred_transfer_characteristics to have the Arib
> value at the same time the standard VUI trc field contains a value like
> BT2020 instead, for device backwards compat purposes?
>
> If both have the Arib value, then it seems redundant.

It is also for robustness，if preferred_transfer_characteristics is
existed but not set, decoder may use
preferred_transfer_characteristics instead of vui
transfer_characteristics.