Add the concept of a "WorkingBeatmap" and make player load beatmaps and audio from SongSelect.

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -0,0 +1,62 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using osu.Framework.Audio.Track;
+using osu.Game.Beatmaps.IO;
+
+namespace osu.Game.Beatmaps
+{
+    public class WorkingBeatmap : IDisposable
+    {
+        public readonly ArchiveReader Reader;
+        public readonly Beatmap Beatmap;
+
+        private AudioTrack track;
+        public AudioTrack Track
+        {
+            get
+            {
+                if (track == null)
+                {
+                    var trackData = Reader.ReadFile(Beatmap.Metadata.AudioFile);
+                    if (trackData != null)
+                        track = new AudioTrackBass(trackData);
+                }
+
+                return track;
+            }
+            set { track = value; }
+        }
+
+        public WorkingBeatmap(Beatmap beatmap, ArchiveReader reader = null)
+        {
+            Beatmap = beatmap;
+            Reader = reader;
+        }
+
+        private bool isDisposed;
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (!isDisposed)
+            {
+                track?.Dispose();
+                Reader?.Dispose();
+
+                isDisposed = true;
+            }
+        }
+
+        ~WorkingBeatmap()
+        {
+            Dispose(false);
+        }
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+    }
+}