At the transmitter a coder includes a motion vector generator providing vectors (MV) describing the movement of individual blocks of pixels. The video signal is 4:1 compressed in bandwidth by pre-filters and a sub-sampling unit to produce a signal (SSH) from which a high-definition image can be re-constructed in the coder and in the decoder. The sampling lattice is shifted in accordance with the motion vectors (MV) which are digitally transmitted along with the compressed bandwidth analogue signal, to enable the samples to be correctly located in the reconstructed image. Poorly correlated moving areas are handled by pure spatial filtering (pre-filter and sub-sampling unit) with reconstruction by spatial interpolation. The two reconstructed signals (RVH and RVL) at the coder are compared in a mode selector with the input video and a switch is set to transmit whichever of the compressed signals (SSH, SSL) gives the best match. A mode signal is also transmitted and, at the receiver decoder this operates a switch to select (RVH') or (RVL') correspondingly for feeding to the display. In a modified embodiment the sub-sampling unit does not employ a moving lattice but all samples for a four field sequence are taken from one field of each sequence.