AK::StreamMgr::IAkIOHookBlocking|Deferred::Write() is needed by the default stream manager's implementation of AK::IAkStdStream::Write(). You need to implement it only if you use this service, or if you use AK::SoundEngine::StartOutputCapture() (because this feature uses AK::IAkStdStream::Write()). Otherwise, you don't need to implement this method because it is never called.