Sorry to bump, but this issue still seems to exist with the iOS 27.1 simulators. I'm trying to update my Metal 4 based app to work with iPhone Duo, and while it compiles fine on my physical iPhone 16 Pro, no dice on the simulator. Getting similar errors as others have posted: "Cannot find type 'MTL4CommandQueue' in scope", "Cannot find type 'MTL4CommandBuffer' in scope" and other similar errors for other MTL4 types. Any update on this? I did submit feedback (FB24868746), but haven't heard anything yet. protocol MetalVisualizerRenderer: AnyObject { var device: MTLDevice { get } var commandQueue: any MTL4CommandQueue { get } var commandBuffer: any MTL4CommandBuffer { get } var sharedEvent: MTLSharedEvent { get } . . .

Sure, will do! Xcode actually already compiled and sent a feedback report, here is the ID: FB22816142.

I got a GPU trace. When running it in Xcode, the replayer crashes with a seg fault. Let me know if you want a copy of the trace, it's rather large so I can't attach it here.

Both approaches work! Thank you so much! I decided to go with the second option as it seems more robust than marking the import with @preconcurrency and just silencing concurrency warnings.

Ah I see, thanks for the explanation! I've already submitted a bug report via Feedback Assistant a few days ago (FB18933857), but have yet to hear anything back.

Please find attached my crash log. I believe this is the right one. VisualMan-2025-07-17-201213.txt

I accidentally selected this reply as an accepted answer, is it possible to undo this action?

I've made a small breakthrough, the code crashes because of the installTap call, but the bad news is that I'm unable to figure out why. Any ideas?

It's been fixed! All I had to do was mark the loadAudioSamples as @MainActor and wrap the processSamples call in a Task.

Actually, I figured it out! Turns our .m4a encodes to dual mono, so I changed the file format to .wav and I have stereo now!