vd: use ST.2086 / HDR10 MaxCLL in addition to mastering metadata

MaxCLL is the more authoritative source for the metadata we are
interested in. The use of mastering metadata is sort of a hack anyway,
since there's no clearly-defined relationship between the mastering peak
brightness and the actual content. (Unlike MaxCLL, which is an explicit
relationship)

Also move the parameter fixing to `fix_image_params`

I don't know if the avutil check is strictly necessary but I've included
it anyway to be on the safe side.

demux/demux_mkv.c

@@ -568,7 +568,12 @@ static void parse_trackcolour(struct demuxer *demuxer, struct mkv_track *track,
         MP_VERBOSE(demuxer, "|    + Levels: %s\n",
                    m_opt_choice_str(mp_csp_levels_names, track->color.levels));
     }
-    if (colour->n_mastering_metadata) {
+    if (colour->n_max_cll) {
+        track->color.sig_peak = colour->max_cll / MP_REF_WHITE;
+        MP_VERBOSE(demuxer, "|    + MaxCLL: %lu\n", colour->max_cll);
+    }
+    // if MaxCLL is unavailable, try falling back to the mastering metadata
+    if (!track->color.sig_peak && colour->n_mastering_metadata) {
         struct ebml_mastering_metadata *mastering = &colour->mastering_metadata;
 
         if (mastering->n_luminance_max) {

video/decode/dec_video.c

@@ -188,6 +188,11 @@ bool video_init_best_codec(struct dec_video *d_video)
     return !!d_video->vd_driver;
 }
 
+static bool is_valid_peak(float sig_peak)
+{
+    return !sig_peak || (sig_peak >= 1 && sig_peak <= 100);
+}
+
 static void fix_image_params(struct dec_video *d_video,
                              struct mp_image_params *params)
 {
@@ -258,8 +263,16 @@ static void fix_image_params(struct dec_video *d_video,
     }
     p.stereo_out = opts->video_stereo_mode;
 
-    // Detect colorspace from resolution.
     mp_colorspace_merge(&p.color, &c->color);
+
+    // Sanitize the HDR peak. Sadly necessary
+    if (!is_valid_peak(p.color.sig_peak)) {
+        MP_WARN(d_video, "Invalid HDR peak in stream: %f\n", p.color.sig_peak);
+        p.color.sig_peak = 0.0;
+    }
+
+    // Guess missing colorspace fields from metadata. This guarantees all
+    // fields are at least set to legal values afterwards.
     mp_image_params_guess_csp(&p);
 
     d_video->last_format = *params;

video/decode/lavc.h

@@ -39,7 +39,7 @@ typedef struct lavc_ctx {
     int framedrop_flags;
 
     // For HDR side-data caching
-    double cached_hdr_peak;
+    float cached_sig_peak;
 
     bool hw_probing;
     struct demux_packet **sent_packets;

video/decode/vd_lavc.c

@@ -721,28 +721,33 @@ static void update_image_params(struct dec_video *vd, AVFrame *frame,
                                 struct mp_image_params *params)
 {
     vd_ffmpeg_ctx *ctx = vd->priv;
+    AVFrameSideData *sd;
 
-#if LIBAVCODEC_VERSION_MICRO >= 100
-    // Get the reference peak (for HDR) if available. This is cached into ctx
-    // when it's found, since it's not available on every frame (and seems to
-    // be only available for keyframes)
-    AVFrameSideData *sd = av_frame_get_side_data(frame,
-                          AV_FRAME_DATA_MASTERING_DISPLAY_METADATA);
+#if HAVE_AVUTIL_CONTENT_LIGHT_LEVEL
+    // Get the content light metadata if available
+    sd = av_frame_get_side_data(frame, AV_FRAME_DATA_CONTENT_LIGHT_LEVEL);
     if (sd) {
-        AVMasteringDisplayMetadata *mdm = (AVMasteringDisplayMetadata *)sd->data;
-        if (mdm->has_luminance) {
-            double peak = av_q2d(mdm->max_luminance);
-            if (!isnormal(peak) || peak < 10 || peak > 100000) {
-                // Invalid data, ignore it. Sadly necessary
-                MP_WARN(vd, "Invalid HDR reference peak in stream: %f\n", peak);
-            } else {
-                ctx->cached_hdr_peak = peak;
-            }
-        }
+        AVContentLightMetadata *clm = (AVContentLightMetadata *)sd->data;
+        params->color.sig_peak = clm->MaxCLL / MP_REF_WHITE;
     }
 #endif
 
-    params->color.sig_peak = ctx->cached_hdr_peak / MP_REF_WHITE;
+#if LIBAVCODEC_VERSION_MICRO >= 100
+    // Otherwise, try getting the mastering metadata if available
+    sd = av_frame_get_side_data(frame, AV_FRAME_DATA_MASTERING_DISPLAY_METADATA);
+    if (!params->color.sig_peak && sd) {
+        AVMasteringDisplayMetadata *mdm = (AVMasteringDisplayMetadata *)sd->data;
+        if (mdm->has_luminance)
+            params->color.sig_peak = av_q2d(mdm->max_luminance) / MP_REF_WHITE;
+    }
+#endif
+
+    if (params->color.sig_peak) {
+        ctx->cached_sig_peak = params->color.sig_peak;
+    } else {
+        params->color.sig_peak = ctx->cached_sig_peak;
+    }
+
     params->rotate = vd->codec->rotate;
     params->stereo_in = vd->codec->stereo_mode;
 }

wscript

@@ -449,6 +449,12 @@ FFmpeg/Libav libraries. You need at least {0}. Aborting.".format(libav_versions_
         'func': check_statement('libavutil/imgutils.h',
                                 'av_image_copy_uc_from(0,0,0,0,0,0,0)',
                                 use='libav'),
+    }, {
+        'name': 'avutil-content-light-level',
+        'desc': 'libavutil content light level struct',
+        'func': check_statement('libavutil/frame.h',
+                                'AV_FRAME_DATA_CONTENT_LIGHT_LEVEL',
+                                use='libav'),
     },
 ]