This is a two parter for an old thread. First the image – this is can be accomplished by offsetting the image frame to frame and cropping. Then the audio can be synched as described above. You’ll lose some definition in the image, but you could shoot at 1080 and edit to 720 or even sd for the final cut.
I run into this when shooting SDI to ssd and AVCHD to sd with the same camera then going to split screen. lining up the shots using an overlay opacity of 50% works fairly well.