Commit fd02c29562 for ffmpeg

commit fd02c2956244381693b2f09b6346d5164f86d624
Author: Kacper Michajłow <kasper93@gmail.com>
Date:   Wed Sep 30 03:05:35 2026 +0200

    avfilter/vf_zscale: negotiate the chroma location

    The output link takes the chromal value, or any location when it is not
    set, in which case the frames are converted to the negotiated one, the
    same way as for the color space and range. The input accepts any location,
    and input without one is assumed to be sited like the output, so it is
    tagged but not converted.

    Signed-off-by: Kacper Michajłow <kasper93@gmail.com>

diff --git a/libavfilter/vf_zscale.c b/libavfilter/vf_zscale.c
index b14d704663..dc14d61e87 100644
--- a/libavfilter/vf_zscale.c
+++ b/libavfilter/vf_zscale.c
@@ -231,6 +231,15 @@ static int query_formats(const AVFilterContext *ctx,
     if ((ret = ff_formats_ref(formats, &cfg_out[0]->color_ranges)) < 0)
         return ret;

+    if ((ret = ff_formats_ref(ff_all_chroma_locations(), &cfg_in[0]->chroma_locations)) < 0)
+        return ret;
+
+    formats = s->chromal != -1
+        ? ff_make_formats_list_singleton(s->chromal + 1)
+        : ff_all_chroma_locations();
+    if ((ret = ff_formats_ref(formats, &cfg_out[0]->chroma_locations)) < 0)
+        return ret;
+
     if ((ret = ff_formats_ref(ff_all_alpha_modes(), &cfg_in[0]->alpha_modes))  < 0 ||
         (ret = ff_formats_ref(ff_all_alpha_modes(), &cfg_out[0]->alpha_modes)) < 0)
         return ret;
@@ -784,6 +793,8 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
         av_frame_copy_props(out, in);
         out->colorspace = outlink->colorspace;
         out->color_range = outlink->color_range;
+        if (outlink->chroma_location != AVCHROMA_LOC_UNSPECIFIED)
+            out->chroma_location = outlink->chroma_location;

         if ((ret = realign_frame(link, desc, &in)) < 0)
             goto fail;
@@ -806,10 +817,13 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
         zimg_image_format_default(&s->dst_format, ZIMG_API_VERSION);
         zimg_graph_builder_params_default(&s->params, ZIMG_API_VERSION);

-        format_init(&s->src_format, in, desc, s->colorspace_in,
-            s->primaries_in, s->trc_in, s->range_in, s->chromal_in);
         format_init(&s->dst_format, out, odesc, s->colorspace,
             s->primaries, s->trc, s->range, s->chromal);
+        /* Input without a chroma location is assumed to be sited like the output. */
+        format_init(&s->src_format, in, desc, s->colorspace_in,
+            s->primaries_in, s->trc_in, s->range_in,
+            s->chromal_in == -1 && in->chroma_location == AVCHROMA_LOC_UNSPECIFIED ?
+            s->dst_format.chroma_location : s->chromal_in);
         s->first_time = 0;

         s->params.dither_type = s->dither;
@@ -883,6 +897,8 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
         }
     } else {
         /*no need for any filtering */
+        if (outlink->chroma_location != AVCHROMA_LOC_UNSPECIFIED)
+            in->chroma_location = outlink->chroma_location;
         return ff_filter_frame(outlink, in);
     }
 fail: