A vertical interview is more than the middle crop of a landscape image. The narrow frame changes how much environment, gesture and distance between people remains visible. Decide before filming whether vertical is the primary version or an additional format alongside a wider edition.
See the actual composition
Use an appropriate framing guide on the camera monitor where available, or check the intended crop by another reliable method. Sit in the interviewee's position and test typical movement. A tight chest-up frame may work when still but lose the hands as soon as an explanation becomes more animated.
If a landscape version is also required, seek a composition that supports both. Not every subject permits this. Two people seated far apart often cannot be transferred sensibly from one wide shot into a narrow frame. Separate shots may provide a clearer solution.
Consider eyeline and background
Leave useful space in the direction of the gaze without pushing the person against the narrow edge. Inspect what appears above and below the face. A conspicuous lamp overhead may dominate a vertical composition more strongly than a landscape one. The background should support the subject rather than continually draw attention away.
Plan room for captions and identification, but do not reserve large empty areas without purpose. Design the full image together with the eventual text. A short test export reveals whether the chin, hands, clothing and captions compete or the person has become unnecessarily small.
Test movement and reframing
If the person demonstrates an object, test its whole path into the image. An item comfortably beside the face in landscape may be cropped in vertical. Rather than asking someone to remain unnaturally still, adjust distance and position so the intended action remains possible.
Automatic reframing can provide a starting point in post-production. Inspect every important moment, however. The tool may follow a face while losing an explanatory hand or product. Small manual corrections are preferable to a crop that chases every movement nervously.
Check the vertical edition independently from the landscape version with captions enabled. The two may use different shot sizes and occasionally different supporting images. What matters is that the same statement remains understandable and no information disappears merely because the delivered frame is narrower.