An .mp4 demonstrating a de Broglie wave associated with a particle moving with velocity \(v\) is in phase with a clock with frequency \(\nu_{0} = \frac{mc^2}{h}\) in the proper frame of the particle and also in phase with a clock with frequency \(\nu=\frac{\nu_{0}}{\sqrt{1-\beta^2}},\ v=c\beta\) in the observer's rest frame.