Same issue for me on all browsers I have tested.

HOWEVER, I am seeing the same "throwing -10878" show up when simply attaching a mixer to the audio engine: audioEngine = AVAudioEngine() mixer = AVAudioMixerNode() audioEngine.attach(mixer) // <-- throwing -10878 occurs here

With your sample code, you can just change the connect line to the one in this stackoverflow answer: https://stackoverflow.com/questions/69414839/in-ios-15-throwing-10878-occurs-many-times-when-connecting-avaudioplayernode

We are seeing the same throwing -10878 with AVFoundation: https://developer.apple.com/forums/thread/692264