Add Custom Extension in Advanced Config

Data/RenderConfig.cs

@@ -1,7 +1,9 @@
+using System.Diagnostics.CodeAnalysis;
 using ADOFAIRenderer.Util.FFmpeg;
 
 namespace ADOFAIRenderer.Data
 {
+    [SuppressMessage("ReSharper", "RedundantDefaultMemberInitializer")]
     public class RenderConfig
     {
         public double RenderFPS { get; set; }
@@ -15,14 +17,16 @@ namespace ADOFAIRenderer.Data
         public AdvancedConfig AdvancedConfig { get; set; } = new();
 
         public double DelayAfterEnd { get; set; }
-        public bool ShowJudgementText { get; set; }
+        public bool ShowJudgementText { get; set; } = false;
     }
 
+    [SuppressMessage("ReSharper", "RedundantDefaultMemberInitializer")]
     public class AdvancedConfig
     {
         public int? RandomSeed { get; set; } = null;
         public bool ProcessAudio { get; set; } = true;
         public bool NonTile { get; set; } = false;
+        public string Extension { get; set; } = "mkv";
     }
 
     public class VideoEncodingConfig