This paper proposes a new solution for simultaneous functional verification system of multiple Set-Top Boxes based on Black Box Testing (BBT). In our work, a methodology and system is proposed, with specially developed software and hardware modules. The proposed framework for simultaneous testing for Set-Top Boxes is implemented with device under test (DUT) preview window. The proposed methodology accelerates verification process and ensures reduction of time and costs, which is crucial in production, and also provides a possibility of testing the receivers during live video stream.