diff --git a/video/out/filter_kernels.h b/video/out/filter_kernels.h
index 3b12fcfe57..b2e07863fd 100644
--- a/video/out/filter_kernels.h
+++ b/video/out/filter_kernels.h
@@ -31,9 +31,8 @@ struct filter_kernel {
     // Whether or not the filter uses polar coordinates
     bool polar;
     // The following values are set by mp_init_filter() at runtime.
-    // Number of coefficients; equals the rounded up radius multiplied with 2.
-    int size;
-    double inv_scale;
+    int size;           // number of coefficients (may depend on radius)
+    double inv_scale;   // scale factor (<1.0 is upscale, >1.0 downscale)
 };
 
 extern const struct filter_kernel mp_filter_kernels[];