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swscale/utils: read dynamic HDR10+ metadata from AVFrame

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Logic ported from libplacebo's AVFrame helpers. The basic idea is to use the
provided MaxRGB/MaxSCL values to infer what the actual luminance would have
been, which HDR10+ metadata does not provide directly. It's worth pointing out
that this gives us an *upper* bound on the true maximum luminance, so any
error in the estimation cannot result in clipping.
This commit is contained in:
Niklas Haas 2024-11-30 14:50:36 +01:00
parent 7432fa19cd
commit 9084d581e8
1 changed files with 50 additions and 0 deletions
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50
libswscale/utils.c
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@ -43,6 +43,7 @@
#include "libavutil/cpu.h"
#include "libavutil/csp.h"
#include "libavutil/emms.h"
#include "libavutil/hdr_dynamic_metadata.h"
#include "libavutil/imgutils.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/libm.h"
@ -2748,6 +2749,55 @@ SwsFormat ff_fmt_from_frame(const AVFrame *frame, int field)
}
}
if ((sd = av_frame_get_side_data(frame, AV_FRAME_DATA_DYNAMIC_HDR_PLUS))) {
const AVDynamicHDRPlus *dhp = (const AVDynamicHDRPlus *) sd->data;
const AVHDRPlusColorTransformParams *pars = &dhp->params[0];
const AVRational nits = av_make_q(10000, 1);
AVRational maxrgb = pars->maxscl[0];
if (!dhp->num_windows || dhp->application_version > 1)
goto skip_hdr10;
/* Maximum of MaxSCL components */
if (av_cmp_q(pars->maxscl[1], maxrgb) > 0)
maxrgb = pars->maxscl[1];
if (av_cmp_q(pars->maxscl[2], maxrgb) > 0)
maxrgb = pars->maxscl[2];
if (maxrgb.num > 0) {
/* Estimate true luminance from MaxSCL */
const AVLumaCoefficients *luma = av_csp_luma_coeffs_from_avcsp(fmt.csp);
if (!luma)
goto skip_hdr10;
fmt.color.frame_peak = av_add_q(av_mul_q(luma->cr, pars->maxscl[0]),
av_add_q(av_mul_q(luma->cg, pars->maxscl[1]),
av_mul_q(luma->cb, pars->maxscl[2])));
/* Scale the scene average brightness by the ratio between the
* maximum luminance and the MaxRGB values */
fmt.color.frame_avg = av_mul_q(pars->average_maxrgb,
av_div_q(fmt.color.frame_peak, maxrgb));
} else {
/**
* Calculate largest value from histogram to use as fallback for
* clips with missing MaxSCL information. Note that this may end
* up picking the "reserved" value at the 5% percentile, which in
* practice appears to track the brightest pixel in the scene.
*/
for (int i = 0; i < pars->num_distribution_maxrgb_percentiles; i++) {
const AVRational pct = pars->distribution_maxrgb[i].percentile;
if (av_cmp_q(pct, maxrgb) > 0)
maxrgb = pct;
fmt.color.frame_peak = maxrgb;
fmt.color.frame_avg = pars->average_maxrgb;
}
}
/* Rescale to nits */
fmt.color.frame_peak = av_mul_q(nits, fmt.color.frame_peak);
fmt.color.frame_avg = av_mul_q(nits, fmt.color.frame_avg);
}
skip_hdr10:
/* PQ is always scaled down to absolute zero, so ignore mastering metadata */
if (fmt.color.trc == AVCOL_TRC_SMPTE2084)
fmt.color.min_luma = av_make_q(0, 1);