Clear ring buffer when no audio is being output.

Author: Devin Roth

BlackHole.xcodeproj/xcshareddata/xcschemes/BlackHole.xcscheme

@@ -0,0 +1,67 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1310"
+   version = "1.3">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "2D7477A81578168D00412279"
+               BuildableName = "BlackHole.driver"
+               BlueprintName = "BlackHole"
+               ReferencedContainer = "container:BlackHole.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES">
+      <Testables>
+      </Testables>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "2D7477A81578168D00412279"
+            BuildableName = "BlackHole.driver"
+            BlueprintName = "BlackHole"
+            ReferencedContainer = "container:BlackHole.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

BlackHole/BlackHole.c

@@ -3779,13 +3779,25 @@ static OSStatus	BlackHole_DoIOOperation(AudioServerPlugInDriverRef inDriver, Aud
         secondPartFrameSize = inIOBufferFrameSize - firstPartFrameSize;
     }
 
+    // Keep track of last outputSampleTime and the cleared buffer status.
+    static Float64 lastOutputSampleTime = 0;
+    static Boolean isBufferClear = true;
+    
     // From BlackHole to Application
     if(inOperationID == kAudioServerPlugInIOOperationReadInput)
     {
-        // If mute is one let's just fill the buffer with zeros
-        if (gMute_Master_Value || gMute_Master_Value)
+        // If mute is one let's just fill the buffer with zeros or if there's no apps outputing audio
+        if (gMute_Master_Value || lastOutputSampleTime - inIOBufferFrameSize < inIOCycleInfo->mInputTime.mSampleTime)
         {
-            memset(ioMainBuffer, 0, inIOBufferFrameSize * kNumber_Of_Channels * sizeof(Float32));
+            // Clear the ioMainBuffer
+            vDSP_vclr(ioMainBuffer, 1, inIOBufferFrameSize * kNumber_Of_Channels);
+            
+            // Clear the ring buffer.
+            if (!isBufferClear)
+            {
+                vDSP_vclr(gRingBuffer, 1, kRing_Buffer_Frame_Size * kNumber_Of_Channels);
+                isBufferClear = true;
+            }
         }
         else
         {
@@ -3803,6 +3815,9 @@ static OSStatus	BlackHole_DoIOOperation(AudioServerPlugInDriverRef inDriver, Aud
     // From Application to BlackHole
     if(inOperationID == kAudioServerPlugInIOOperationWriteMix)
     {
+        // Save the last output time.
+        lastOutputSampleTime= inIOCycleInfo->mOutputTime.mSampleTime;
+        isBufferClear = false;
 
         memcpy(((void*)gRingBuffer) + ringBufferFrameLocationStart * kNumber_Of_Channels * sizeof(Float32), ioMainBuffer, firstPartFrameSize * kNumber_Of_Channels * sizeof(Float32));
         memcpy(gRingBuffer, ioMainBuffer + firstPartFrameSize * kNumber_Of_Channels * sizeof(Float32), secondPartFrameSize * kNumber_Of_Channels * sizeof(Float32));