ScreenCaptureKit System Audio Capture Crashes with EXC_BAD_ACCESS

Bug Report: ScreenCaptureKit System Audio Capture Crashes with EXC_BAD_ACCESS

Summary

When using ScreenCaptureKit to capture system audio for extended periods, the application crashes with EXC_BAD_ACCESS in Swift's error handling runtime. The crash occurs in swift_getErrorValue when trying to process an error from the SCStream delegate method didStopWithError. This appears to be a framework-level issue in ScreenCaptureKit or its underlying ReplayKit implementation.

Environment

• macOS Sonoma 14.6.1
• Swift 5.8
• ScreenCaptureKit framework

Detailed Description

Our application captures system audio using ScreenCaptureKit's audio capture capabilities. After successfully capturing for several minutes (typically after 3-4 segments of 60-second recordings), the application crashes with an EXC_BAD_ACCESS error. The crash happens when the Swift runtime attempts to process an error in the SCStreamDelegate.stream(_:didStopWithError:) method.

The crash consistently occurs in swift_getErrorValue when attempting to access the class of what appears to be a null object. This suggests that the error being passed from the system framework to our delegate method is malformed or contains invalid memory.

Steps to Reproduce

1. Create an SCStream with audio capture enabled
2. Add audio output to the stream
3. Start capture and write audio data to disk
4. Allow the capture to run for several minutes (3-5 minutes typically triggers the issue)
5. The app will crash with EXC_BAD_ACCESS in swift_getErrorValue

Code Sample

    
    func stream(_ stream: SCStream, didStopWithError error: Error) {
        print("Stream stopped with error: \(error)") // Crash occurs before this line executes
    }
    
    func stream(_ stream: SCStream, didOutputSampleBuffer sampleBuffer: CMSampleBuffer, of type: SCStreamOutputType) {
        guard type == .audio, sampleBuffer.isValid else { return }
        // Process audio data...
    }

Expected Behavior

The error should be properly propagated to the delegate method, allowing for graceful error handling and recovery.

Actual Behavior

The application crashes with EXC_BAD_ACCESS when the Swift runtime attempts to process the error in swift_getErrorValue.

Crash Log Details

Thread #35, queue = 'com.apple.NSXPCConnection.m-user.com.apple.replayd', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  frame #0: 0x0000000194c3088c libswiftCore.dylib`swift::_swift_getClass(void const*) + 8
  frame #1: 0x0000000194c30104 libswiftCore.dylib`swift_getErrorValue + 40
  frame #2: 0x00000001057fba30 shadow`NewScreenCaptureService.stream(stream=0x0000600002de6700, error=Swift.Error @ 0x000000016b7b5e30) at NEW+ScreenCaptureService.swift:365:15
  frame #3: 0x00000001057fc050 shadow`@objc NewScreenCaptureService.stream(_:didStopWithError:) at <compiler-generated>:0
  frame #4: 0x0000000219ec5ca0 ScreenCaptureKit`-[SCStreamManager stream:didStopWithError:] + 456
  frame #5: 0x00000001ca68a5cc ReplayKit`-[RPScreenRecorder stream:didStopWithError:] + 84
  frame #6: 0x00000001ca696ff8 ReplayKit`-[RPDaemonProxy stream:didStopWithError:] + 224

Printing description of stream._streamQueue:
error: ObjectiveC.id:4294967281:18: note: 'id' has been explicitly marked unavailable here
public typealias id = AnyObject
                 ^
error: /var/folders/v4/3xg1hmp93gjd8_xlzmryf_wm0000gn/T/expr23-dfa421..cpp:1:65: 'id' is unavailable in Swift: 'id' is not available in Swift; use 'Any'
Swift._DebuggerSupport.stringForPrintObject(Swift.UnsafePointer<id>(bitPattern: 0x104ae08c0)!.pointee)
                                                                ^~
ObjectiveC.id:2:18: note: 'id' has been explicitly marked unavailable here
public typealias id = AnyObject
                 ^
warning: /var/folders/v4/3xg1hmp93gjd8_xlzmryf_wm0000gn/T/expr23-dfa421..cpp:5:7: initialization of variable '$__lldb_error_result' was never used; consider replacing with assignment to '_' or removing it
  var $__lldb_error_result = __lldb_tmp_error
  ~~~~^~~~~~~~~~~~~~~~~~~~
  _

Before the crash, we observed this error message in the console:

[ERROR] *****SCStream*****RemoteAudioQueueOperationHandlerWithError:1015 Error received from the remote queue -16665

Additional Context

• The issue occurs consistently after approximately 3-4 successful audio segment recordings of 60 seconds each
• Commenting out custom segment rotation logic does not prevent the crash
• The crash involves XPC communication with Apple's ReplayKit daemon
• The error appears to be corrupted or malformed when crossing the XPC boundary

Workarounds Attempted

1. Added proper thread safety for all published properties using DispatchQueue.main.async
2. Implemented more robust error handling in the delegate methods

None of these approaches prevented the crash since it occurs at the Swift runtime level before our code executes.

Impact

This issue prevents reliable long-duration audio capture using ScreenCaptureKit.

This bug significantly limits the usefulness of ScreenCaptureKit for any application requiring continuous system audio capture for more than a few minutes.

Perhaps this issue might be related to a macOS bug where the system dialog indicates that the screen is being shared, even though nothing is actually being shared. Moreover, when attempting to stop sharing, nothing happens.