Three ratios cover almost everything. Wide landscape is what you want for anything watched on a computer or a television, for embedding on your website, and for longer content where the viewer settles in. Vertical, filling a phone screen held upright, is now the dominant format for short social video and is what the recommendation systems on those platforms favour, which affects reach rather than merely presentation. Square sits between them and survives being placed almost anywhere without looking wrong, which makes it a reasonable default when you genuinely do not know the destination.
The practical technique that saves the most rework is filming wide while framing for the crop. Shoot in landscape but compose your subject in the centre with room above and below, so a vertical version can be pulled from the same footage without losing anything important. Many cameras and phones will show guides for this. It costs nothing at the time and it converts one shoot into material for several places.
Where this matters most is text on screen. Captions, titles, and anything written positioned near the edge of a frame will disappear when the video is cropped for another platform, and it disappears silently. Keep anything essential well inside the centre of the frame, and check the cropped version before publishing rather than trusting that it survived.
If you only ever film one way, choose based on where your audience actually is rather than on what feels more professional. For a business whose customers discover things on phones, vertical will reach more people than a beautifully composed landscape video that the platform shows in a small box. The reach difference on short social video is large enough that it outweighs most other considerations.
One habit prevents most of the rework, which is deciding where a video will be published before you press record rather than afterward. That single decision determines the framing, the length, and whether captions need to survive a crop, and making it in advance costs nothing while making it later means either accepting a bad crop or filming again. Businesses that produce video consistently almost always have this settled before the camera comes out, and businesses that find video exhausting usually do not.