Validate Even Render Resolution Before Starting

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

UI/Window/RenderConfigWindow.cs

@@ -846,6 +846,14 @@ internal static class RenderConfigWindow
         var config = UiConfig;
         SyncUItoConfig(config);
 
+        // The encoders use 4:2:0 chroma subsampling, which needs an even width and height.
+        if (config.RenderWidth % 2 != 0 || config.RenderHeight % 2 != 0)
+        {
+            ShowValidationError(LocalizationManager.Get(
+                "ui.render_config.validation_even_size", config.RenderWidth, config.RenderHeight));
+            return;
+        }
+
         // Sync Output Directory
         if (_outputDirInput != null)
         {