Video recordings offer great opportunities for qualitative social science research; their epistemological status, however, has not been left unchallenged. The paper picks up on this methodological debate, sounding out the specific potential of this research medium. Yet instead of primarily participating in methodological debates, we particularly want to inquire into the underlying empirical notions, settings, actors, and sceneries, which inform methodological debates on video. Reviewing research on ‘professional vision’ in Science and Technology Studies we try to raise awareness of the constructive nature of the practices, which manufacture and transform visual traces into evidence. We then look at our own research practice and ask about epistemic topologies which enable video to become a research medium. We will thus try to identify the resources, practices, and things – epistemic mediators – that make other things (video recordings) act like epistemic objects, and, with the help of concepts by Hennion and Law, we look at these networks of mediators and their respective ways of mediation as ‘media assemblages’.