diff --git a/BizHawk.Client.Common/movie/tasproj/TasLagLog.cs b/BizHawk.Client.Common/movie/tasproj/TasLagLog.cs
index 4d7fea83b2..e6a4f7e9d9 100644
--- a/BizHawk.Client.Common/movie/tasproj/TasLagLog.cs
+++ b/BizHawk.Client.Common/movie/tasproj/TasLagLog.cs
@@ -1,37 +1,91 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 
 namespace BizHawk.Client.Common
 {
-	public class TasLagLog : List<bool>
+	public class TasLagLog
 	{
+		private readonly SortedList<int, bool> LagLog = new SortedList<int, bool>();
+
+		public bool? this[int frame]
+		{
+			get
+			{
+				if (LagLog.ContainsKey(frame))
+				{
+					return LagLog[frame];
+				}
+
+				return null;
+			}
+
+			set
+			{
+				if (!value.HasValue)
+				{
+					LagLog.Remove(frame);
+				}
+				else if (frame < 0)
+				{
+					return; // Nothing to do
+				}
+				else if (LagLog.ContainsKey(frame))
+				{
+					LagLog[frame] = value.Value;
+				}
+				else
+				{
+					LagLog.Add(frame, value.Value);
+				}
+			}
+		}
+
+		public bool HasLagEntry(int frame)
+		{
+			return LagLog.ContainsKey(frame);
+		}
+
+		public void Clear()
+		{
+			LagLog.Clear();
+		}
+
 		public void RemoveFrom(int frame)
 		{
-			if (frame > 0 && frame <= this.Count)
+			if (frame > 0 && frame <= LagLog.Count)
 			{
-				this.RemoveRange(frame - 1, this.Count - (frame - 1));
+				for (int i = LagLog.Count - 1; i > frame; i--) // Reverse order because removing from a sorted list re-indexes the items after the removed item
+				{
+					LagLog.RemoveAt(i);
+				}
 			}
 			else if (frame == 0)
 			{
 				this.Clear();
 			}
+
 		}
 
-		public bool? Lagged(int index)
+		public void Save(BinaryWriter bw)
 		{
-			// Hacky but effective, we haven't record the lag information for the current frame yet
-			if (index == Global.Emulator.Frame - 1)
+			bw.Write(LagLog.Count);
+			foreach (var kvp in LagLog)
 			{
-				return Global.Emulator.IsLagFrame;
-			}
-			
-			if (index < this.Count)
-			{
-				return this[index];
+				bw.Write(kvp.Key);
+				bw.Write(kvp.Value);
 			}
+		}
 
-			return null;
+		public void Load(BinaryReader br)
+		{
+			LagLog.Clear();
+			int length = br.ReadInt32();
+			for (int i = 0; i < length; i++)
+			{
+				LagLog.Add(br.ReadInt32(), br.ReadBoolean());
+			}
 		}
 	}
 }
diff --git a/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs b/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs
index cefecf5caf..3d5e591134 100644
--- a/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs
+++ b/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs
@@ -14,11 +14,8 @@ namespace BizHawk.Client.Common
 		{
 			base.RecordFrame(frame, source);
 
-			if (frame > 0)
-			{
-				LagLog.RemoveFrom(frame);
-				LagLog.Add(Global.Emulator.IsLagFrame);
-			}
+			LagLog.RemoveFrom(frame);
+			LagLog[frame] = Global.Emulator.IsLagFrame;
 
 			StateManager.Capture();
 		}
diff --git a/BizHawk.Client.Common/movie/tasproj/TasMovie.IO.cs b/BizHawk.Client.Common/movie/tasproj/TasMovie.IO.cs
index a4dcc21cd8..7f0536f130 100644
--- a/BizHawk.Client.Common/movie/tasproj/TasMovie.IO.cs
+++ b/BizHawk.Client.Common/movie/tasproj/TasMovie.IO.cs
@@ -40,7 +40,7 @@ namespace BizHawk.Client.Common
 					bs.PutLump(BinaryStateLump.Greenzone, (BinaryWriter bw) => StateManager.Save(bw));
 				}
 
-				bs.PutLump(BinaryStateLump.LagLog, (BinaryWriter bw) => bw.Write(LagLog.ToByteArray()));
+				bs.PutLump(BinaryStateLump.LagLog, (BinaryWriter bw) => LagLog.Save(bw));
 				bs.PutLump(BinaryStateLump.Markers, tw => tw.WriteLine(Markers.ToString()));
 
 				if (StartsFromSavestate)
@@ -163,10 +163,13 @@ namespace BizHawk.Client.Common
 				}
 
 				// TasMovie enhanced information
-				bl.GetLump(BinaryStateLump.LagLog, false, delegate(BinaryReader br, long length)
+				if (bl.HasLump(BinaryStateLump.LagLog))
 				{
-					LagLog.AddRange(br.ReadBytes((int)length).ToBools());
-				});
+					bl.GetLump(BinaryStateLump.LagLog, false, delegate(BinaryReader br, long length)
+					{
+						LagLog.Load(br);
+					});
+				}
 
 				bl.GetLump(BinaryStateLump.GreenzoneSettings, false, delegate(TextReader tr)
 				{
diff --git a/BizHawk.Client.Common/movie/tasproj/TasMovie.cs b/BizHawk.Client.Common/movie/tasproj/TasMovie.cs
index 28c0a621ab..b5518ea4fb 100644
--- a/BizHawk.Client.Common/movie/tasproj/TasMovie.cs
+++ b/BizHawk.Client.Common/movie/tasproj/TasMovie.cs
@@ -63,7 +63,7 @@ namespace BizHawk.Client.Common
 				{
 					State = StateManager[index],
 					LogEntry = GetInputLogEntry(index),
-					Lagged = LagLog.Lagged(index)
+					Lagged = LagLog[index]
 				};
 			}
 		}
@@ -287,16 +287,9 @@ namespace BizHawk.Client.Common
 
 		public override IController GetInputState(int frame)
 		{
-			if (Global.Emulator.Frame - 1 == frame)
-			{
-				if (frame == LagLog.Count) // I intentionally did not do >=, if it were >= we missed some entries somewhere, oops, maybe this shoudl be a dictionary<int, bool> with frame values?
-				{
-					LagLog.Add(Global.Emulator.IsLagFrame);
-				}
-			}
-
-			if (Global.Emulator.Frame == frame) // Take this opportunity to capture lag and state info if we do not have it
+			if (frame == Global.Emulator.Frame) // Take this opportunity to capture lag and state info if we do not have it
 			{
+				LagLog[Global.Emulator.Frame] = Global.Emulator.IsLagFrame;
 
 				if (!StateManager.HasState(frame))
 				{