Why platforms disagree on the right shape for video
Landscape 16:9 remains standard for traditional video viewing (YouTube, TVs, desktop playback), vertical 9:16 dominates mobile-first short-form platforms, and square 1:1 is a common middle ground for feed posts that need to look reasonable regardless of whether the viewer's screen is portrait or landscape. A single piece of content increasingly needs versions in two or three of these shapes to perform well across the full range of places it might be published.
This fragmentation isn't going away — different platforms optimized for different viewing contexts (holding a phone vertically while scrolling vs. watching on a horizontal screen), and each shape genuinely works better in its intended context, which is exactly why one universal aspect ratio hasn't won out.
Three real approaches to changing aspect ratio
Cropping cuts the frame down to fit the new shape, sacrificing whatever falls outside the new boundaries — this works well when the important content is centered and there's nothing critical near the edges you're cutting away. Adding padding (letterboxing or pillarboxing) keeps the entire original frame intact by adding bars to fill the new shape, preserving all the content but leaving visible empty space, often filled with a blurred or color-matched background rather than plain black or white for a more polished look. Stretching distorts the image to force it into a new shape without cropping or padding — this is rarely the right choice, since it visibly warps proportions and looks obviously wrong.
For most content, cropping (when the subject is well-centered) or padding with a matched background (when cropping would cut something important) are the two genuinely viable options — stretching should be treated as a last resort, not a default.
Planning for multiple aspect ratios from the start
If you know content will need to exist in multiple shapes, filming or framing with that in mind — keeping the most important subject matter centered, avoiding critical text or action right at the edges of a wide frame — makes every subsequent aspect ratio conversion cleaner. Retrofitting multi-format compatibility onto footage that was framed for a single specific shape is always more constrained than planning for it upfront.
One conversion rarely serves every platform equally well
A single 9:16 crop optimized for one vertical platform's specific safe zones (where UI elements like captions or buttons overlay the video) may not be ideally framed for a different vertical platform with different overlay positions — if a piece of content is genuinely important across multiple platforms, checking each platform's specific safe-zone recommendations before finalizing a crop is worth the extra step, rather than assuming one 9:16 version works identically everywhere.