vd_lavc: respect lavc's color_trc field

We now actually use the TRC tagging information lavc provides us with,
instead of always manually guessing.

video/csputils.h

@@ -203,6 +203,8 @@ enum mp_csp_levels avcol_range_to_mp_csp_levels(int avrange);
 
 enum mp_csp_prim avcol_pri_to_mp_csp_prim(int avpri);
 
+enum mp_csp_trc avcol_trc_to_mp_csp_trc(int avtrc);
+
 int mp_csp_to_avcol_spc(enum mp_csp colorspace);
 
 int mp_csp_levels_to_avcol_range(enum mp_csp_levels range);

video/decode/vd_lavc.c

@@ -477,6 +477,7 @@ static void update_image_params(struct dec_video *vd, AVFrame *frame,
         .colorspace = avcol_spc_to_mp_csp(ctx->avctx->colorspace),
         .colorlevels = avcol_range_to_mp_csp_levels(ctx->avctx->color_range),
         .primaries = avcol_pri_to_mp_csp_prim(ctx->avctx->color_primaries),
+        .gamma = avcol_trc_to_mp_csp_trc(ctx->avctx->color_trc),
         .chroma_location =
             avchroma_location_to_mp(ctx->avctx->chroma_sample_location),
         .rotate = vd->header->video->rotate,