A system and method for evaluating a video signal comprising a plurality of video frames. In the plurality video frames, the number of pixels changed from one frame to the next are analysed and each frame is identified as being a repeat if a set proportion of the pixels present in the current frame match those present in the previous frame. The resultant pattern of repeat frames in the video signal is recorded. The resultant pattern is then scanned to determine whether or not a given repeat frame is part of a temporally repetitive pattern and those repeat frames not determined to be part of the temporally repetitive pattern are identified. As result of the above, video quality assessment is able to treat these two types of temporal artefact separately so as to distinguish between the almost invisible regular frame loss and the visually disturbing irregular frame loss.