Add pad video filter

FFMpegCore.Test/ArgumentBuilderTest.cs

@@ -495,5 +495,45 @@ public void Builder_BuildString_Audible_AAXC_Decryption()
 
             Assert.AreEqual("-audible_key 123 -audible_iv 456 -i \"input.aaxc\" -map_metadata 0 -id3v2_version 3 -vn -c:a copy \"output.m4b\" -y", str);
         }
+
+        [TestMethod]
+        public void Builder_BuildString_PadFilter()
+        {
+            var str = FFMpegArguments
+                .FromFileInput("input.mp4")
+                .OutputToFile("output.mp4", false, opt => opt
+                    .WithVideoFilters(filterOptions => filterOptions
+                        .Pad(PadOptions
+                            .Create("max(iw,ih)", "ow")
+                            .WithParameter("x", "(ow-iw)/2")
+                            .WithParameter("y", "(oh-ih)/2")
+                            .WithParameter("color", "violet")
+                            .WithParameter("eval", "frame"))))
+                .Arguments;
+
+            Assert.AreEqual(
+                "-i \"input.mp4\" -vf \"pad=width=max(iw\\,ih):height=ow:x=(ow-iw)/2:y=(oh-ih)/2:color=violet:eval=frame\" \"output.mp4\"",
+                str);
+        }
+
+        [TestMethod]
+        public void Builder_BuildString_PadFilter_Alt()
+        {
+            var str = FFMpegArguments
+                .FromFileInput("input.mp4")
+                .OutputToFile("output.mp4", false, opt => opt
+                    .WithVideoFilters(filterOptions => filterOptions
+                        .Pad(PadOptions
+                            .Create("4/3")
+                            .WithParameter("x", "(ow-iw)/2")
+                            .WithParameter("y", "(oh-ih)/2")
+                            .WithParameter("color", "violet")
+                            .WithParameter("eval", "frame"))))
+                .Arguments;
+
+            Assert.AreEqual(
+                "-i \"input.mp4\" -vf \"pad=aspect=4/3:x=(ow-iw)/2:y=(oh-ih)/2:color=violet:eval=frame\" \"output.mp4\"",
+                str);
+        }
     }
 }

FFMpegCore/FFMpeg/Arguments/PadArgument.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using FFMpegCore.Extend;
+
+namespace FFMpegCore.Arguments
+{
+    public class PadArgument : IVideoFilterArgument
+    {
+        private readonly PadOptions _options;
+
+        public PadArgument(PadOptions options)
+        {
+            _options = options;
+        }
+
+        public string Key => "pad";
+        public string Value => _options.TextInternal;
+
+    }
+
+    public class PadOptions
+    {
+        public readonly Dictionary<string, string> Parameters = new Dictionary<string, string>();
+
+        internal string TextInternal => string.Join(":", Parameters.Select(parameter => parameter.FormatArgumentPair(true)));
+
+        public static PadOptions Create(string? width, string? height)
+        {
+            return new PadOptions(width, height);
+        }
+
+        public static PadOptions Create(string aspectRatio)
+        {
+            return new PadOptions(aspectRatio);
+        }
+
+        public PadOptions WithParameter(string key, string value)
+        {
+            Parameters.Add(key, value);
+            return this;
+        }
+
+        private PadOptions(string? width, string? height)
+        {
+            if (width == null && height == null)
+            {
+                throw new Exception("At least one of the parameters must be not null");
+            }
+            if (width != null)
+            {
+                Parameters.Add("width", width);
+            }
+            if (height != null)
+            {
+                Parameters.Add("height", height);
+            }
+        }
+
+        private PadOptions(string aspectRatio)
+        {
+            Parameters.Add("aspect", aspectRatio);
+        }
+    }
+}

FFMpegCore/FFMpeg/Arguments/VideoFiltersArgument.cs

@@ -53,6 +53,7 @@ public class VideoFilterOptions
         public VideoFilterOptions HardBurnSubtitle(SubtitleHardBurnOptions subtitleHardBurnOptions) => WithArgument(new SubtitleHardBurnArgument(subtitleHardBurnOptions));
         public VideoFilterOptions BlackDetect(double minimumDuration = 2.0, double pictureBlackRatioThreshold = 0.98, double pixelBlackThreshold = 0.1) => WithArgument(new BlackDetectArgument(minimumDuration, pictureBlackRatioThreshold, pixelBlackThreshold));
         public VideoFilterOptions BlackFrame(int amount = 98, int threshold = 32) => WithArgument(new BlackFrameArgument(amount, threshold));
+        public VideoFilterOptions Pad(PadOptions padOptions) => WithArgument(new PadArgument(padOptions));
 
         private VideoFilterOptions WithArgument(IVideoFilterArgument argument)
         {