1. A method of measuring blocking artefacts on the basis of video data encoded in accordance with a block-based encoding technique, the method comprising the steps of: computing a mono-dimensional inverse discrete transform of a first row of a first block of encoded video data, suitable for supplying a value of a first virtual border pixel; computing a mono-dimensional inverse discrete transform of a first row of a second block of encoded video data, the second block being adjacent to the first block, suitable for supplying a value of a second virtual border pixel; and computing a blocking artefact level on the basis of an absolute value of a difference between the values of the first and second virtual pixels.