Add FFMetadataBuilder for easily constructing metadata text

FFMpegCore/FFMetadataInputArgument.cs

@@ -0,0 +1,63 @@
+using System.Text;
+
+namespace FFMpegCore;
+
+public class FFMetadataBuilder
+{
+    private Dictionary<string, string> Tags { get; } = new();
+    private List<FFMetadataChapter> Chapters { get; } = [];
+
+    public static FFMetadataBuilder Empty()
+    {
+        return new FFMetadataBuilder();
+    }
+
+    public FFMetadataBuilder WithTag(string key, string value)
+    {
+        Tags.Add(key, value);
+        return this;
+    }
+
+    public FFMetadataBuilder WithChapter(string title, long durationMs)
+    {
+        Chapters.Add(new FFMetadataChapter(title, durationMs));
+        return this;
+    }
+
+    public FFMetadataBuilder WithChapter(string title, double durationSeconds)
+    {
+        Chapters.Add(new FFMetadataChapter(title, Convert.ToInt64(durationSeconds * 1000)));
+        return this;
+    }
+
+    public string GetMetadataFileContent()
+    {
+        var sb = new StringBuilder();
+        sb.AppendLine(";FFMETADATA1");
+
+        foreach (var tag in Tags)
+        {
+            sb.AppendLine($"{tag.Key}={tag.Value}");
+        }
+
+        long totalDurationMs = 0;
+        foreach (var chapter in Chapters)
+        {
+            sb.AppendLine("[CHAPTER]");
+            sb.AppendLine("TIMEBASE=1/1000");
+            sb.AppendLine($"START={totalDurationMs}");
+            sb.AppendLine($"END={totalDurationMs + chapter.DurationMs}");
+            sb.AppendLine($"title={chapter.Title}");
+            totalDurationMs += chapter.DurationMs;
+        }
+
+        return sb.ToString();
+    }
+
+
+    private class FFMetadataChapter(string title, long durationMs)
+    {
+        public string Title { get; } = title;
+        public long DurationMs { get; } = durationMs;
+    }
+}