Abstract: A method and an apparatus for sampling a reference signal so as to generate an error signal indicative of a phase error between an actual sampling phase and a desired sampling phase. The desired sampling phase is displaceable from an optimum sampling phase, so as to facilitate the sampling of an NTSC color burst signal or to effect hue control during sampling of the modulated chroma sub-carrier. The reference signal is sampled at the frequency of said signal and a plurality of said samples are accumulated. After said samples have been accumulated, said accumulation is multiplied by the sine or by the cosine of the phase displacement angle between the optimum sampling phase and the derived sampling phase.

Abstract: A mixer for combining digital video signals allows four real-time signals to be combined. At each layer, a digital key signal may be generated from the input video signal using chroma or luminance keying. In addition, the video signal may be combined with drop shadows, a border and a fill to produce first-stage composite video and composite key signals. A composite key signal is produced by supplying two key signals to a comparator and a selector via respective switchable invertors. The comparator produces a selection signal which is supplied to the selector via a switchable invertor. The selector switches an input signal to produce an output signal which is supplied to an output port via a switchable converter.