Add first draft of keyframe extraction for Matroska

src/Jellyfin.MediaEncoding.Keyframes/Matroska/Models/SeekHead.cs

@@ -0,0 +1,36 @@
+namespace Jellyfin.MediaEncoding.Keyframes.Matroska.Models
+{
+    /// <summary>
+    /// The matroska SeekHead segment. All positions are relative to the Segment container.
+    /// </summary>
+    internal class SeekHead
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SeekHead"/> class.
+        /// </summary>
+        /// <param name="infoPosition">The relative file position of the info segment.</param>
+        /// <param name="tracksPosition">The relative file position of the tracks segment.</param>
+        /// <param name="cuesPosition">The relative file position of the cues segment.</param>
+        public SeekHead(long infoPosition, long tracksPosition, long cuesPosition)
+        {
+            InfoPosition = infoPosition;
+            TracksPosition = tracksPosition;
+            CuesPosition = cuesPosition;
+        }
+
+        /// <summary>
+        /// Gets relative file position of the info segment.
+        /// </summary>
+        public long InfoPosition { get; }
+
+        /// <summary>
+        /// Gets the relative file position of the tracks segment.
+        /// </summary>
+        public long TracksPosition { get; }
+
+        /// <summary>
+        /// Gets the relative file position of the cues segment.
+        /// </summary>
+        public long CuesPosition { get; }
+    }
+}