update legacy hd homerun support

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -179,6 +179,11 @@ namespace MediaBrowser.Controller.MediaEncoding
             {
                 return null;
             }
+            // Seeing reported failures here, not sure yet if this is related to specfying input format
+            if (string.Equals(container, "m4v", StringComparison.OrdinalIgnoreCase))
+            {
+                return null;
+            }
 
             return container;
         }