add an IStatable extension method that will return a byte array that's safe to hold on to, but isn't optimized for speed, to be used in basic situations where we are making movies from savestate or getting a savestate length

src/BizHawk.Client.Common/movie/tasproj/TasStateManager.cs

@@ -47,7 +47,7 @@ namespace BizHawk.Client.Common
 
 			_decay = new StateManagerDecay(_movie, this);
 
-			_expectedStateSize = (ulong)Core.SaveStateBinary().Length;
+			_expectedStateSize = (ulong)Core.CloneSavestate().Length; // TODO: why do we store this in a ulong?
 			if (_expectedStateSize == 0)
 			{
 				throw new InvalidOperationException("Savestate size can not be zero!");

src/BizHawk.Client.EmuHawk/config/RewindConfig.cs

@@ -42,7 +42,7 @@ namespace BizHawk.Client.EmuHawk
 			RewindSpeedNumeric.Value = _config.Rewind.SpeedMultiplier;
 			DiskBufferCheckbox.Checked = _config.Rewind.OnDisk;
 			RewindIsThreadedCheckbox.Checked = _config.Rewind.IsThreaded;
-			_stateSize = _statableCore.SaveStateBinary().Length;
+			_stateSize = _statableCore.CloneSavestate().Length;
 			BufferSizeUpDown.Value = Math.Max(_config.Rewind.BufferSize, BufferSizeUpDown.Minimum);
 
 			_mediumStateSize = _config.Rewind.MediumStateSize;

src/BizHawk.Client.EmuHawk/movie/RecordMovie.cs

@@ -109,7 +109,7 @@ namespace BizHawk.Client.EmuHawk
 
 					if (_config.SaveStateType == SaveStateTypeE.Binary)
 					{
-						movieToRecord.BinarySavestate = (byte[])core.SaveStateBinary().Clone();
+						movieToRecord.BinarySavestate = core.CloneSavestate();
 					}
 					else
 					{

src/BizHawk.Client.EmuHawk/tools/TAStudio/GreenzoneSettings.cs

@@ -82,7 +82,7 @@ namespace BizHawk.Client.EmuHawk
 
 		private void MemStateGapDivider_ValueChanged(object sender, EventArgs e)
 		{
-			int val = (int)(Statable.SaveStateBinary().Length / MemStateGapDividerNumeric.Value / 1024);
+			int val = (int)(Statable.CloneSavestate().Length / MemStateGapDividerNumeric.Value / 1024);
 
 			if (val <= 1)
 				MemStateGapDividerNumeric.Maximum = MemStateGapDividerNumeric.Value;

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.MenuItems.cs

@@ -7,6 +7,7 @@ using System.Windows.Forms;
 using BizHawk.Client.Common;
 using BizHawk.Client.Common.MovieConversionExtensions;
 using BizHawk.Client.EmuHawk.ToolExtensions;
+using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.EmuHawk
 {
@@ -38,10 +39,8 @@ namespace BizHawk.Client.EmuHawk
 		{
 			if (AskSaveChanges())
 			{
-				int index = Emulator.Frame;
-
 				 var newProject = CurrentTasMovie.ConvertToSavestateAnchoredMovie(
-					index, (byte[])StatableEmulator.SaveStateBinary().Clone());
+					Emulator.Frame, StatableEmulator.CloneSavestate());
 
 				MainForm.PauseEmulator();
 				LoadFile(new FileInfo(newProject.Filename), true);
@@ -752,7 +751,7 @@ namespace BizHawk.Client.EmuHawk
 
 				if (CurrentTasMovie.TasStateManager.HasState(Emulator.Frame))
 				{
-					byte[] state = (byte[])StatableEmulator.SaveStateBinary().Clone();
+					byte[] state = StatableEmulator.CloneSavestate();
 					byte[] greenZone = CurrentTasMovie.TasStateManager[Emulator.Frame];
 
 					if (!state.SequenceEqual(greenZone))

src/BizHawk.Emulation.Common/Interfaces/Services/IStatable.cs

@@ -87,5 +87,20 @@ namespace BizHawk.Emulation.Common
 			using var br = new BinaryReader(ms);
 			core.LoadStateBinary(br);
 		}
+
+		/// <summary>
+		/// Creates a byte array copy of the core's current state
+		/// This creates a new buffer, and should not be used in performance sensitive situations
+		/// </summary>
+		public static byte[] CloneSavestate(this IStatable core)
+		{
+			using var ms = new MemoryStream();
+			using var bw = new BinaryWriter(ms);
+			core.SaveStateBinary(bw);
+			bw.Flush();
+			var stateBuffer = ms.ToArray();
+			bw.Close();
+			return stateBuffer;
+		}
 	}
 }