Aspect ratio converting circuits store a digital signal at a first clock rate into a memory, wherein the digital signal represents a picture having a first aspect ratio. In the first mode, the digital signal is retrieved from the memory during one horizontal period on the basis of the first clock rate....http://www.google.de/patents/US5856849?utm_source=gb-gplus-sharePatent US5856849 - Digital processing of video signals for performing aspect ratio conversion
