Pairing questions within Different Blocks

I am conducting an experiment where participants watch a video "A", answer some questions, then watch a second video "B" and answer additional questions. I am able to randomize the videos so they only see one "A" video and one "B" video, but certain videos need to be paired so that the same respondent sees the same condition for both videos. How do I pair the videos to ensure that participants see video ["A1" and "B1"] or ["A2" and "B2"] etc. as opposed to "A1" and "B3" for example?