Posible problem cvQueryFrame (Bug #2635)
May be a problem when execute the method cvQueryFrame in a diferente thread then the main thread under macOs (Snow leopard 10.6.8).
The problem occur when Execute the method that call cvQueryFrame using the Apple method perforSelectorInBackground (that detach a new thread that execute the method passing as argument). The use should be like these:
[obj performSelectorInBackground:@selector(method) withObject:nil]. In the Method will call cvQueryFrame but ill try to debbug and Always get a null frame if execute using performSelectorInBackground to execute my method in a diferent thread