A method of transmitting video signals comprising: storing a plurality of reference frames in a buffer coding input video frames and transmitting them to a decoder, said coding being performed by, for at least some of the frames, choosing one or more of the stored reference frames and coding at least part of the input video frames using inter-frame differential coding relative thereto; and locally decoding the coded input video frames to generate locally decoded frames for storage as said reference frames; wherein the method includes receiving error messages and in response thereto suppressing the use of relatively younger reference frames as predictor and to choose only relatively older frames for prediction; wherein said reference frames are stored in a buffer having a storage capacity less than the round trip time to the decoder divided by the frame period; and wherein said method includes the step of selecting a reference frame to be deleted from the buffer to make place for a newly-decoded frame; characterised in that said selection being made in accordance with a time window having a duration of a plurality of frame periods and timed such that the youngest buffered frame in the window is older than the current frame by a time interval of at least the round trip time divided by the frame period, according to the following rules: (a) if there is only one buffered frame falling within the defined time window, that frame shall not be deleted; and (b) a frame shall not be deleted if the time difference between the next oldest frame in the buffer and the next youngest frame in the buffer exceeds the duration of the time window. storing a plurality of reference frames in a buffer coding input video frames and transmitting them to a decoder, said coding being performed by, for at least some of the frames, choosing one or more of the stored reference frames and coding at least part of the input video frames using inter-frame differential coding relative thereto; and locally decoding the coded input video frames to generate locally decoded frames for storage as said reference frames; wherein the method includes receiving error messages and in response thereto suppressing the use of relatively younger reference frames as predictor and to choose only relatively older frames for prediction; wherein said reference frames are stored in a buffer having a storage capacity less than the round trip time to the decoder divided by the frame period; and wherein said method includes the step of selecting a reference frame to be deleted from the buffer to make place for a newly-decoded frame; characterised in that said selection being made in accordance with a time window having a duration of a plurality of frame periods and timed such that the youngest buffered frame in the window is older than the current frame by a time interval of at least the round trip time divided by the frame period, according to the following rules: (a) if there is only one buffered frame falling within the defined time window, that frame shall not be deleted; and (b) a frame shall not be deleted if the time difference between the next oldest frame in the buffer and the next youngest frame in the buffer exceeds the duration of the time window. (a) if there is only one buffered frame falling within the defined time window, that frame shall not be deleted; and (b) a frame shall not be deleted if the time difference between the next oldest frame in the buffer and the next youngest frame in the buffer exceeds the duration of the time window.