Pause audio while in a TAS for cassettes

Source/Audio/Audio.cs

@@ -1,5 +1,5 @@
+using Celeste64.TAS;
 using FMOD.Studio;
-using System.Diagnostics;
 using System.Reflection;
 using System.Runtime.InteropServices;
 
@@ -9,7 +9,7 @@ public static class Audio
 {
 	private class Module : Foster.Framework.Module
 	{
-		public override void Update() 
+		public override void Update()
 			=> Audio.Update();
 
 		public override void Shutdown()
@@ -21,6 +21,9 @@ public override void Shutdown()
 	private static readonly Dictionary<string, FMOD.GUID> events = [];
 	private static readonly Dictionary<string, FMOD.GUID> buses = [];
 
+    private static FMOD.ChannelGroup masterChannelGroup;
+    internal static FMOD.DSP dsp;
+
 	public static void Init()
 	{
 		// live upate allows FMOD UI to interact with sounds in-game in real time
@@ -50,9 +53,72 @@ public static void Init()
 		// Initialize FMOD
 		Check(system.initialize(1024, studioFlags, flags, IntPtr.Zero));
 
+        var desc = default(FMOD.DSP_DESCRIPTION);
+        desc.version = 0x00010000;
+        desc.numinputbuffers = 1;
+        desc.numoutputbuffers = 1;
+        desc.read = BlockCallback;
+
+        core.getMasterChannelGroup(out masterChannelGroup);
+        core.createDSP(ref desc, out dsp);
+        masterChannelGroup.addDSP(0, dsp);
+        dsp.setBypass(true);
+
 		App.Register<Module>();
 	}
 
+    // Theoretical perfect amount of samples per frame
+    private const int TargetRecordedSamples = 48000 / 60;
+    // Blocks the FMOD thread.
+    internal static bool blockEnabled = false;
+    // The accumulated overhead, since audio chunks contain more data than 1 frame.
+    private static int totalRecodedSamplesError = 0;
+    // Actual amount of samples which were blocked
+    private static int recordedSamples = 0;
+
+    private static unsafe FMOD.RESULT BlockCallback(ref FMOD.DSP_STATE dspState, IntPtr inBuffer, IntPtr outBuffer, uint samples, int inChannels, ref int outChannels) {
+        float* src = (float*) inBuffer;
+        float* dst = (float*) outBuffer;
+
+        if (inChannels == outChannels) {
+            NativeMemory.Copy(src, dst, (nuint) (inChannels * samples * Marshal.SizeOf<float>()));
+        } else if (inChannels > outChannels) {
+            // Cut the remaining channels off
+            for (int sample = 0; sample < samples; sample++) {
+                NativeMemory.Copy(src + sample * inChannels, dst + sample * outChannels, (nuint) (outChannels * Marshal.SizeOf<float>()));
+            }
+        } else {
+            // Repeat the last channel to fill the remaining ones
+            for (int sample = 0; sample < samples; sample++) {
+                NativeMemory.Copy(src + sample * inChannels, dst + sample * outChannels, (nuint) (inChannels * Marshal.SizeOf<float>()));
+                for (int channel = inChannels; channel < outChannels; channel++) {
+                    dst![sample * outChannels + channel] = src![sample * inChannels + inChannels - 1];
+                }
+            }
+        }
+
+        recordedSamples += (int) samples;
+
+        // Skip a frame to let the video catch up again
+        if (totalRecodedSamplesError >= TargetRecordedSamples) {
+            totalRecodedSamplesError -= TargetRecordedSamples;
+            recordedSamples = 0;
+            return FMOD.RESULT.OK;
+        }
+
+        if (recordedSamples >= TargetRecordedSamples)
+            blockEnabled = true;
+
+        // Block until the TAS allows resuming. (also blocks the main FMOD thread which is good, since it avoid artifacts)
+        while (blockEnabled && Manager.Running) { }
+
+        // Account for overshooting
+        totalRecodedSamplesError += recordedSamples - TargetRecordedSamples;
+        recordedSamples = 0;
+
+        return FMOD.RESULT.OK;
+    }
+
 	private static bool isResolverSet = false;
 
 	private static void LoadDynamicLibraries()
@@ -61,11 +127,11 @@ private static void LoadDynamicLibraries()
 			return;
 		isResolverSet = true;
 
-		var path 
-			=  Path.GetDirectoryName(AppContext.BaseDirectory) 
+		var path
+			=  Path.GetDirectoryName(AppContext.BaseDirectory)
 			?? Directory.GetCurrentDirectory();
 
-		NativeLibrary.SetDllImportResolver(typeof(FMOD.Studio.System).Assembly, 
+		NativeLibrary.SetDllImportResolver(typeof(FMOD.Studio.System).Assembly,
 			(name, assembly, dllImportSearchPath) =>
 			{
 				name = Path.GetFileNameWithoutExtension(name);
@@ -210,7 +276,7 @@ private static AudioHandle Create(in EventDescription desc)
 			Log.Warning($"Failed to create Audio Event Instance: {result}");
 			return new AudioHandle();
 		}
-		
+
 		return new AudioHandle(instance);
 	}
 
@@ -309,4 +375,4 @@ public static ulong ParameterIDToU64(PARAMETER_ID id)
 		return ((ulong)id.data1 << 32) | (id.data2);
 	}
 
-}
+}

Source/Game.cs

@@ -157,6 +157,9 @@ public override void Update()
             return;
         }
 
+        // Allow for next audio frame
+        Audio.blockEnabled = false;
+
         // update top scene
         if (scenes.TryPeek(out var scene))
         {

Source/TAS/Manager.cs

@@ -53,6 +53,8 @@ public static void EnableRun()
         Controller.RefreshInputs();
 
         TASLevelRecord.ID = string.Empty;
+
+        Audio.dsp.setBypass(false);
     }
 
     public static void DisableRun()
@@ -63,6 +65,8 @@ public static void DisableRun()
         NextState = State.Disabled;
         AttributeUtils.Invoke<DisableRunAttribute>();
         Controller.Stop();
+
+        Audio.dsp.setBypass(true);
     }
 
     public static void Update()