system performance of picture - in - picture video display systems is dependent on critical timing relationships between the incoming signals and the clock signals used to sample and display both the large picture and small picture signals . video signals from various sources , e . g . vtr &# 39 ; s , tend to have jittering time bases which may cause the small image to appear jagged or tilted . this distortion in the small image may be reduced by effecting adaptive signal delays in the small picture signal responsive to the relative phase of the system clock signal with respect to the horizontal synchronizing pulses of the large and / or small picture signal . one phase measure is used to control an interpolator which combines successive samples of the small picture signal in proportions to develop sample values corresponding to samples that would have occurred had the small picture signal been sampled by a clock properly aligned to the small picture horizontal synchronizing pulses . a second phase measure is used to delay the clock signal used to display the small picture so that the clock pulses that define the edges of the small picture occurs with the same timing relative to the large picture horizontal synchronizing pulses form line - to - line .