1 files changed, 87 insertions, 0 deletions
diff --git a/src/Jellyfin.MediaEncoding.Keyframes/Matroska/MatroskaKeyframeExtractor.cs b/src/Jellyfin.MediaEncoding.Keyframes/Matroska/MatroskaKeyframeExtractor.cs
new file mode 100644
index 000000000..501b2bb17
--- /dev/null
+++ b/src/Jellyfin.MediaEncoding.Keyframes/Matroska/MatroskaKeyframeExtractor.cs
@@ -0,0 +1,87 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Jellyfin.MediaEncoding.Keyframes.Matroska.Extensions;
+using Jellyfin.MediaEncoding.Keyframes.Matroska.Models;
+using NEbml.Core;
+
+namespace Jellyfin.MediaEncoding.Keyframes.Matroska;
+
+/// <summary>
+/// The keyframe extractor for the matroska container.
+/// </summary>
+public static class MatroskaKeyframeExtractor
+{
+    /// <summary>
+    /// Extracts the keyframes in ticks (scaled using the container timestamp scale) from the matroska container.
+    /// </summary>
+    /// <param name="filePath">The file path.</param>
+    /// <returns>An instance of <see cref="KeyframeData"/>.</returns>
+    public static KeyframeData GetKeyframeData(string filePath)
+    {
+        using var stream = File.OpenRead(filePath);
+        using var reader = new EbmlReader(stream);
+
+        var seekHead = reader.ReadSeekHead();
+        // External lib does not support seeking backwards (yet)
+        Info info;
+        ulong videoTrackNumber;
+        if (seekHead.InfoPosition < seekHead.TracksPosition)
+        {
+            info = reader.ReadInfo(seekHead.InfoPosition);
+            videoTrackNumber = reader.FindFirstTrackNumberByType(seekHead.TracksPosition, MatroskaConstants.TrackTypeVideo);
+        }
+        else
+        {
+            videoTrackNumber = reader.FindFirstTrackNumberByType(seekHead.TracksPosition, MatroskaConstants.TrackTypeVideo);
+            info = reader.ReadInfo(seekHead.InfoPosition);
+        }
+
+        var keyframes = new List<long>();
+        reader.ReadAt(seekHead.CuesPosition);
+        reader.EnterContainer();
+
+        while (reader.FindElement(MatroskaConstants.CuePoint))
+        {
+            reader.EnterContainer();
+            ulong? trackNumber = null;
+            // Mandatory element
+            reader.FindElement(MatroskaConstants.CueTime);
+            var cueTime = reader.ReadUInt();
+
+            // Mandatory element
+            reader.FindElement(MatroskaConstants.CueTrackPositions);
+            reader.EnterContainer();
+            if (reader.FindElement(MatroskaConstants.CuePointTrackNumber))
+            {
+                trackNumber = reader.ReadUInt();
+            }
+
+            reader.LeaveContainer();
+
+            if (trackNumber == videoTrackNumber)
+            {
+                keyframes.Add(ScaleToTicks(cueTime, info.TimestampScale));
+            }
+
+            reader.LeaveContainer();
+        }
+
+        reader.LeaveContainer();
+
+        var result = new KeyframeData(ScaleToTicks(info.Duration ?? 0, info.TimestampScale), keyframes);
+        return result;
+    }
+
+    private static long ScaleToTicks(ulong unscaledValue, long timestampScale)
+    {
+        // TimestampScale is in nanoseconds, scale it to get the value in ticks, 1 tick == 100 ns
+        return (long)unscaledValue * timestampScale / 100;
+    }
+
+    private static long ScaleToTicks(double unscaledValue, long timestampScale)
+    {
+        // TimestampScale is in nanoseconds, scale it to get the value in ticks, 1 tick == 100 ns
+        return Convert.ToInt64(unscaledValue * timestampScale / 100);
+    }
+}