A test sequence (1) comprises multiple pictures (20, 22, 24, 26) comprising at least one respective intra pixel block (30, 32, 34, 36) at a respective dedicated pixel position in the pictures (20, 22, 24, 26). Such a position in a first picture (20) is different from the position of the intra block (32) in a second picture (22) of the sequence. The sequence (1) is transmitted to a user terminal (200) where it is employed for testing the quality of the data communication. By rendering the pictures (20, 22, 24, 26) packet losses are identifiable as missing pixel blocks (30, 332, 34, 36) in the media presentation (60).