Implement Filter-Before-Capture Structure

Util/FFmpeg/FFmpegProcess.cs

@@ -15,7 +15,7 @@ namespace ADOFAIRenderer.Util.FFmpeg
 
         public bool IsEnd => _ffmpegProcess is { HasExited: true };
 
-        public void Execute(string command)
+        protected void Execute(string command)
         {
             if (string.IsNullOrEmpty(command))
             {
@@ -39,7 +39,7 @@ namespace ADOFAIRenderer.Util.FFmpeg
         public void SendDataFromBuffer(byte[] buffer, int length = -1)
         {
             if (_inputStream == null) return;
-            int writeLength = length < 0 ? buffer.Length : length;
+            var writeLength = length < 0 ? buffer.Length : length;
             _inputStream.Write(buffer, 0, writeLength);
             _inputStream.Flush();
         }