diff --git a/YoutubeDl.Wpf/ViewModels/HomeViewModel.cs b/YoutubeDl.Wpf/ViewModels/HomeViewModel.cs
index 83acfa5b3..4a42c5b2d 100644
--- a/YoutubeDl.Wpf/ViewModels/HomeViewModel.cs
+++ b/YoutubeDl.Wpf/ViewModels/HomeViewModel.cs
@@ -266,6 +266,11 @@ private void StartDownload()
                         dlProcess.StartInfo.ArgumentList.Add("--merge-output-format");
                         dlProcess.StartInfo.ArgumentList.Add($"{Settings.Container}");
                     }
+                    else if (Settings.Format.Contains("AV1 + Opus WebM"))
+                    {
+                        dlProcess.StartInfo.ArgumentList.Add("--merge-output-format");
+                        dlProcess.StartInfo.ArgumentList.Add("webm");
+                    }
                 }
                 else if (Settings.Container != "Auto") // custom container
                 {