A video signal mixing apparatus for mixing a playback composite video signal produced by playing a recording medium and a graphics composite video signal generated on the basis of video data read from a memory device, wherein a vertical synchronizing signal of the playback composite video signal is forcedly...http://www.google.com.hk/patents/US5434676?utm_source=gb-gplus-share專利 US5434676 - Apparatus for mixing video signals having different numbers of lines
