diff --git a/Services/Compositor/SceneCompositor.cs b/Services/Compositor/SceneCompositor.cs
index bf0a7ba..3b0444d 100644
--- a/Services/Compositor/SceneCompositor.cs
+++ b/Services/Compositor/SceneCompositor.cs
@@ -396,17 +396,17 @@ public sealed class SceneCompositor
         var x1 = System.Math.Min(cropW, px + dw);
         var y1 = System.Math.Min(cropH, py + dh);
         if (x0 >= x1 || y0 >= y1) return;
-        var d = buffer.AsSpan();
         var s = raster.BgraPixels;
-        for (var y = y0; y < y1; y++)
+        var parallelOpts = new ParallelOptions { MaxDegreeOfParallelism = 4 };
+        Parallel.For(y0, y1, parallelOpts, y =>
         {
             var si = ((y - py) * dw + (x0 - px)) * 4;
             var len = x1 - x0;
             if (op == 256)
-                BlendRowOpaque(d, (y * cropW + x0) * 4, s.AsSpan(si, len * 4), 0, len);
+                BlendRowOpaque(buffer, (y * cropW + x0) * 4, s, si, len);
             else
-                BlendRowWeighted(d, (y * cropW + x0) * 4, s.AsSpan(si, len * 4), 0, len, op);
-        }
+                BlendRowWeighted(buffer, (y * cropW + x0) * 4, s, si, len, op);
+        });
     }
 
     /// <summary>Copy <paramref name="frame"/> and blit a global overlay onto the copy
@@ -823,12 +823,13 @@ public sealed class SceneCompositor
         var dy0 = Math.Max(0, sy0 - options.SourceRectY);
         var dx1 = Math.Min(dstW, sx0 - options.SourceRectX + overlay.Width);
         var dy1 = Math.Min(dstH, sy0 - options.SourceRectY + overlay.Height);
-        for (var y = dy0; y < dy1; y++)
+        var parallelOpts = new ParallelOptions { MaxDegreeOfParallelism = 4 };
+        Parallel.For(dy0, dy1, parallelOpts, y =>
         {
             var si = ((y + options.SourceRectY - sy0) * overlay.Width
                 + dx0 + options.SourceRectX - sx0) * 4;
             BlendRowOpaque(dst, (y * dstW + dx0) * 4, overlay.BgraPixels, si, dx1 - dx0);
-        }
+        });
     }
 
     /// <summary>Straight-alpha source-over blend; the frame's alpha (and the layer opacity) drives coverage.</summary>