A system and same method are provided for producing video signal timing to a display apparatus that has different input/output image/video format. In addition to an image scaler, the system comprises a clock adjuster including a first and a second clock generator. The first clock generator generates a first clock signal by which the input/source pixel data included in the input/source image frame are received. The second clock signal is generated and adjusted to have an average clock period such that the ratio of the input and output frame rates is substantially kept constant. Thus, the skew between the source/input images and the display/output images can be adjusted, and the output frame repeating and/or dropping can be avoided.