Apparatus for processing a video signal

A composite video signal each line of which comprises a line synchronising pulse, a front and a back porch and a vision portion, the synchronising pulse of which may contain a burst of pulsed additional information is applied to an input terminal (1) which is connected to the input of a first signal path (T1, T2) whose output is connected to a current source (I1) and to an output terminal (8). A second signal path (T3, T4) has its input connected to a reference voltage input (5) and its output connected to the current source (I1) and the output terminal (8). A switching circuit (T5, T6) alternately enables the first and second signal paths (T1, T2; T3, T4) under the control of a switching signal at a connection (10) such that the output terminal (8) produces a composite video signal in which the synchronising pulse at the input terminal is replaced by a pulse or level. The replacement does not contain the burst of pulsed additional information when present in the applied signal.