Aspect ratio is the shape of your video frame: how wide it is compared to how tall. Get it right and your clip fills the screen on the platform you are posting to. Get it wrong and you end up with black bars, awkward crops, or a subject pushed out of frame. This guide explains what 9:16, 1:1, and 16:9 mean, when to use each, and how to switch between them in Supercut by typing a prompt, with nothing uploaded.
Aspect ratio is written as width:height. A 16:9 frame is 16 units wide for every 9 units tall, so it is a wide rectangle. A 9:16 frame flips that to a tall rectangle, and 1:1 is a perfect square. The numbers are a ratio, not a resolution: 1920x1080 and 1280x720 are both 16:9 because the proportions match. When your video's shape does not match the space a platform gives it, the player either adds bars to pad the gap or crops the edges to fill it. Choosing the right ratio up front keeps the frame full and your subject where you want it.
Use 9:16 (vertical, tall) for full-screen mobile feeds. TikTok, Instagram Reels, and YouTube Shorts are all built around it. It fills a phone held upright and gives you the most screen space where most people watch. Use 16:9 (wide, landscape) for YouTube, desktop viewing, presentations, and most TVs. It suits interviews, tutorials, gameplay, and anything filmed on a normal camera held sideways. Use 1:1 (square) as the safe middle ground for in-feed posts on Instagram and Facebook and for embeds where you do not control the orientation. A square takes more vertical space in a scrolling feed than a wide clip without committing to a full vertical crop.
There are two ways to change a frame's shape, and they do different things. Cropping (also called reframing) cuts away part of the picture so the subject fits the new ratio, for example taking a wide 16:9 clip and reframing it to 9:16 for Reels. You keep full-screen impact but lose the edges, so the subject can drift out of frame if the camera moves. Resizing fits the whole picture inside the new frame and pads the rest, adding bars on the sides (pillarbox) or top and bottom (letterbox). The rule of thumb: crop or reframe when you want the subject to fill the screen, and resize with padding when you need to keep everything in shot. Supercut can do both, and its smart reframe uses on-device face tracking to keep the subject centered as they move.
In Supercut you do not scrub a timeline or drag crop handles. You drop a clip into the editor and type what you want in plain English. An AI plans the edit, then a deterministic engine maps your request to the exact frame operation. Everything decodes, reframes, and exports in your browser through WebAssembly, so your footage is never uploaded. The only thing sent over the network is your text prompt, so the tool knows the target shape. Supercut also ships platform export presets for TikTok, Reels, Shorts, Twitter, and Discord, so you can ask for a format by name instead of remembering the numbers.
Open the Supercut editor and drag in your video. It loads straight into your browser. Nothing uploads, and you can try your first export without an account.
Describe the target shape in plain English, like "reframe this to 9:16 for TikTok," "crop to a 1:1 square," or "resize to 16:9 with padding." For moving subjects, ask for smart reframe so on-device face tracking keeps them centered.
The reframe runs on your device and shows you the output. Check that the subject sits where you want and nothing important got cut off. If it is too tight, ask to adjust the crop or switch to a resize with padding.
Export the reframed clip and download it. The whole edit happened in your browser, so your footage never left your machine. Your first export is free to try. A paid plan unlocks unlimited watermark-free exports, from 4.99/mo billed yearly, 9.99/mo monthly, or 199 one-time lifetime.
Crop and reframe any video to 9:16 for TikTok, Reels and Shorts. Subject-tracking keeps the action in frame, all in your browser, no upload.
Change video resolution and dimensions in your browser. Downscale for smaller files or match platform sizes, your footage never uploads.
Edit videos for TikTok in your browser. Auto 9:16 reframe, captions, and export, your footage never uploads to TikTok or anyone else first.
Reframe, caption, and batch-process client clips in your browser. No uploading client footage to a third party, and no watermark on paid exports.
Reframe to 9:16, add viral captions, trim hooks, and export TikTok-ready clips in your browser. No upload before you post.
They are the same ratio flipped. 16:9 is wide (landscape), used for YouTube and desktop. 9:16 is tall (vertical), used for TikTok, Reels, and Shorts. Switching between them means cropping away part of the picture or padding it to fit the new shape.
9:16 vertical. It fills a phone held upright and gives you the full screen on the feeds where most people watch. Supercut has presets for each platform, so you can ask to reframe for TikTok, Reels, or Shorts by name.
Changing the shape does not degrade the picture by itself. You only lose the edges that get cropped away when you crop. You choose the export settings, so you stay in control of the final resolution and file size.
No. Supercut decodes, reframes, and exports entirely in your browser using WebAssembly. Your footage never leaves your device. Only the text of your prompt is sent so the AI knows which ratio you want.
Use smart reframe, which tracks faces on-device and keeps the subject centered as they move. Filming with headroom and a centered subject also gives the crop more room to work with.