Thanks for the question about best practices for adding a video and the file that should be edited. There is a no best practice for adding a video as the themes are created to be responsive without a video file being taken into accout. Adding the video may require editing the code that is part of the theme, we do not have any recommended code for the change,
Apologies for the delay in this answer. For some reason, you were not re-directed to the new BoldGrid Support page when you asked your question. Questions that were not supposed to go this older system are being addressed. So, again, our sincere apologies for the confusion.
There are no updates to the video issue as per my reply. Custom coding would be required for additional functionality like having a row/section with a video background. Responsive design means that the design would need to be able to handle a change in screen size and adding a video background would cause issues that could affect the responsiveness.