remove Storyboard from Beatmap, add it to WorkingBeatmap

osu.Game/Beatmaps/Beatmap.cs

@@ -41,11 +41,6 @@ namespace osu.Game.Beatmaps
         /// </summary>
         public double TotalBreakTime => Breaks.Sum(b => b.Duration);
 
-        /// <summary>
-        /// The Beatmap's Storyboard.
-        /// </summary>
-        public Storyboard Storyboard = new Storyboard();
-
         /// <summary>
         /// Constructs a new beatmap.
         /// </summary>
@@ -57,7 +52,6 @@ namespace osu.Game.Beatmaps
             Breaks = original?.Breaks ?? Breaks;
             ComboColors = original?.ComboColors ?? ComboColors;
             HitObjects = original?.HitObjects ?? HitObjects;
-            Storyboard = original?.Storyboard ?? Storyboard;
 
             if (original == null && Metadata == null)
             {

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -35,6 +35,7 @@ namespace osu.Game.Beatmaps
             background = new AsyncLazy<Texture>(populateBackground);
             track = new AsyncLazy<Track>(populateTrack);
             waveform = new AsyncLazy<Waveform>(populateWaveform);
+            storyboard = new AsyncLazy<Storyboard>(populateStoryboard);
         }
 
         protected abstract Beatmap GetBeatmap();
@@ -86,6 +87,13 @@ namespace osu.Game.Beatmaps
 
         private Waveform populateWaveform() => GetWaveform();
 
+        public bool StoryboardLoaded => storyboard.IsValueCreated;
+        public Storyboard Storyboard => storyboard.Value.Result;
+        public async Task<Storyboard> GetStoryboardAsync() => await storyboard.Value;
+        private readonly AsyncLazy<Storyboard> storyboard;
+
+        private Storyboard populateStoryboard() => GetStoryboard();
+
         public void TransferTo(WorkingBeatmap other)
         {
             if (track.IsValueCreated && Track != null && BeatmapInfo.AudioEquals(other.BeatmapInfo))
@@ -99,6 +107,7 @@ namespace osu.Game.Beatmaps
         {
             if (BackgroundLoaded) Background?.Dispose();
             if (WaveformLoaded) Waveform?.Dispose();
+            if (StoryboardLoaded) Storyboard?.Dispose();
         }
 
         public void DisposeTrack()

osu.Game/Storyboards/Storyboard.cs

@@ -5,10 +5,11 @@ using osu.Game.Beatmaps;
 using osu.Game.Storyboards.Drawables;
 using System.Collections.Generic;
 using System.Linq;
+using System;
 
 namespace osu.Game.Storyboards
 {
-    public class Storyboard
+    public class Storyboard : IDisposable
     {
         private readonly Dictionary<string, StoryboardLayer> layers = new Dictionary<string, StoryboardLayer>();
         public IEnumerable<StoryboardLayer> Layers => layers.Values;
@@ -59,5 +60,29 @@ namespace osu.Game.Storyboards
             }
             return drawable;
         }
+
+        #region Disposal
+
+        ~Storyboard()
+        {
+            Dispose(false);
+        }
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        private bool isDisposed;
+
+        protected virtual void Dispose(bool isDisposing)
+        {
+            if (isDisposed)
+                return;
+            isDisposed = true;
+        }
+
+        #endregion
     }
 }