In general, this is fundamentally a legal question rather than an academic one. Most copyright systems only cover material which has been fixed, “printed” or published, so an off-the-cuff talk will likely create a different set of issues from a pre-written recording, especially one which followed the text of the submitted paper closely and thus showed most evidence of “copying” between the two, but you’d need to talk to a copyright lawyer to sort out the nuances.
From the journal’s side it will all depend to a great extent on the licensing system they use (or that you choose to use). If you assign them copyright and they demand true exclusivity, then there could be some theoretical problems Whether any journal would actually attempt to enforce their rights would depend on whether there was any actual chance of money on the case, as well as if there is a business model left to protect.
Edit: For those querying how copyright could be relevant, consider the case where the video is essentially an ”audiobook” of the paper, while the image shows the figures. A pure change of medium isn’t always transformative enough to avoid a potential liability.