Re: [FFmpeg-devel] [PATCH] avcodec/h2645_sei: loosen up min luminance requirements

[Kacper Michajlow <kasper93@gmail.com>]

On Sat, 25 May 2024 at 13:36, Niklas Haas <ffmpeg@haasn.xyz> wrote:
>
> From: Niklas Haas <git@haasn.dev>
>
> The H.265 specification is quite clear on this case:
>
> > When min_display_mastering_luminance is not in the range of 1 to
> > 50000, the nominal maximum display luminance of the mastering display
> > is unknown or unspecified or specified by other means not specified in
> > this Specification.
>
> And so the current code is correct in marking luminance data as invalid
> if min luminance is set to 0. However, this breaks playback of at least
> several real-world Blu-ray releases, for example La La Land, Planet of
> the Apes, and quite possibly a lot more. These come with ostensibly
> valid max_luminance tags (1000 nits), but min_luminance set to 0.
>
> Loosen up this requirement by guarding it behind FF_COMPLIANCE_STRICT.
> We still reject blatantly invalid metadata (wrong value range on
> luminance, max set to 0, max below min, min above 50 nits etc.), so this
> shouldn't cause any unintended regressions.
>
> Fixes: https://github.com/mpv-player/mpv/issues/14177
> ---
>  libavcodec/h2645_sei.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/h2645_sei.c b/libavcodec/h2645_sei.c
> index 1deb76c765..7c83747cd0 100644
> --- a/libavcodec/h2645_sei.c
> +++ b/libavcodec/h2645_sei.c
> @@ -619,11 +619,15 @@ static int h2645_sei_to_side_data(AVCodecContext *avctx, H2645SEI *sei,
>
>              metadata->min_luminance.num = sei->mastering_display.min_luminance;
>              metadata->min_luminance.den = luma_den;
> -            metadata->has_luminance &= sei->mastering_display.min_luminance >= 1 &&
> -                                       sei->mastering_display.min_luminance <= 50000 &&
> +            metadata->has_luminance &= sei->mastering_display.min_luminance <= 50000 &&
>                                         sei->mastering_display.min_luminance <
>                                         sei->mastering_display.max_luminance;
>
> +            /* Real (blu-ray) releases in the wild come with minimum luminance
> +             * values of 0.000 cd/m2, so permit this edge case */
> +            if (avctx->strict_std_compliance >= FF_COMPLIANCE_STRICT)
> +                metadata->has_luminance &= sei->mastering_display.min_luminance >= 1;
> +
>              if (metadata->has_luminance || metadata->has_primaries)
>                  av_log(avctx, AV_LOG_DEBUG, "Mastering Display Metadata:\n");
>              if (metadata->has_primaries) {
> --
> 2.45.0

LGTM

- Kacper
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