Support for crf

Former-commit-id: 170aefeb32

FFMpegCore/FFMPEG/Argument/Atoms/ConstantRateFactorArgument.cs

@@ -0,0 +1,41 @@
+using System;
+
+namespace FFMpegCore.FFMPEG.Argument
+{
+    /// <summary>
+    /// Constant Rate Factor (CRF) argument
+    /// </summary>
+    public class ConstantRateFactorArgument : Argument<int>
+    {
+        public ConstantRateFactorArgument(int crf) : base(crf)
+        {
+            if (crf < 0 || crf > 63)
+            {
+                throw new ArgumentException("Argument is outside range (0 - 63)", nameof(crf));
+            }
+        }
+
+        public override string GetStringValue()
+        {
+            return $"-crf {Value} ";
+        }
+    }
+    /// <summary>
+    /// Constant Rate Factor (CRF) argument
+    /// </summary>
+    public class Variable : Argument<int>
+    {
+        public ConstantRateFactorArgument(int crf) : base(crf)
+        {
+            if (crf < 0 || crf > 63)
+            {
+                throw new ArgumentException("Argument is outside range (0 - 63)", nameof(crf));
+            }
+        }
+
+        public override string GetStringValue()
+        {
+            return $"-crf {Value} ";
+        }
+    }
+}