AnyTool
Your files never leave your device. All processing happens locally in your browser.

How do I change a video's aspect ratio for social without uploading it?

Open AnyTool's Video Aspect Ratio tool, drop in a clip, and pick 16:9, 9:16, 1:1, 4:5, 4:3 (or a custom ratio). Choose Fit to letterbox with blurred or solid-color bars, Fill to crop, or Stretch — a live preview shows the reframe before you export an MP4. Everything runs in your browser with a self-hosted ffmpeg engine: no upload, no CDN, no watermark.

  • Presets 16:9, 9:16, 1:1, 4:5, 4:3, or custom
  • Fit (blurred/solid bars), Fill (crop) or Stretch with live preview
  • Self-hosted ffmpeg engine — no CDN, no upload
  • 100% in your browser — no signup, no watermark

What is

Aspect ratio change

Changing a video's aspect ratio reframes it to a different width-to-height shape (such as 16:9 landscape or 9:16 vertical) by letterboxing with bars (Fit), cropping to fill (Fill) or stretching the image. It is the core step in reframing footage for different social platforms. Client-side reframing runs the encoder in the browser, so the file is never uploaded.

Video Tools

Related terms

16:99:16letterboxcropffmpeg

How to Change a Video's Aspect Ratio

Reframe a clip to a new aspect ratio in your browser.

30 secWeb browser
  1. 1

    Add a video

    Drop in a clip — it stays on your device.

  2. 2

    Pick a ratio and mode

    Choose 16:9, 9:16, 1:1, 4:5, 4:3 or custom, then Fit, Fill or Stretch.

  3. 3

    Export

    Preview the reframe and download the MP4 — nothing is uploaded.

Result: A reframed MP4 video

Frequently Asked Questions

Pick the 9:16 preset and choose Fill to crop or Fit to add bars.

Fill crops the sides for a full-frame vertical video, while Fit keeps the whole frame with blurred or solid bars; a live preview shows the result before export.

Fit adds bars to keep the whole frame, Fill crops to fill the new shape, and Stretch distorts the image to fit.

Fit bars can be blurred or a solid color; Fill loses the cropped edges; Stretch keeps everything but changes proportions.

No — the reframe runs entirely in your browser with a self-hosted engine.

The clip never leaves your device and there is no size cap, signup or watermark.

Detailed Explanation

Methodology

How the Video Aspect Ratio Changer Works

AnyTool changes a video's aspect ratio entirely in the browser using a self-hosted single-threaded ffmpeg.wasm engine — the core (ffmpeg-core.js + the 32 MB wasm) is bundled from npm and served as a same-origin asset, so nothing is fetched from a CDN. Three modes drive the ffmpeg filter graph: Fit scales the clip to fit the target frame and pads the remainder — either a blurred scaled copy of the video (a split feeds a gblur, which is then composited under the clip with overlay) or a solid color via pad=color; Fill scales up and crops the overflow with the crop filter; Stretch simply scales to the exact target. Every output dimension is snapped to an even number (H.264 requires it) and re-encoded as H.264 video with AAC audio in an MP4. Single-threaded is deliberate: the multi-threaded core needs SharedArrayBuffer + cross-origin isolation (COOP/COEP), which would block cross-origin ad iframes, so it is avoided.

  • Runs client-side — the video is never uploaded
  • Self-hosted ffmpeg core (bundled) — no CDN
  • Fit (pad), Fill (scale + crop), or Stretch modes
  • Padding is a blurred scaled copy (split + gblur + overlay) or a solid color (pad=color)
  • Even-dimension snap for H.264; H.264 + AAC MP4 output
  • Single-threaded (keeps ads working); no backend, no cap
Privacy & Security

Privacy vs Upload-based Tools

Most online aspect-ratio changers upload your file to a server and cap the free tier or add a watermark. AnyTool reframes locally with a bundled engine, so the video never leaves your browser, there is no size limit, no watermark and no signup, and it works offline after the first load.

Aspect ratio change: AnyTool vs typical tools
CapabilityAnyToolTypical tools
Data handlingIn your browserOften uploaded
Engine sourceSelf-hosted (no CDN)CDN / server
Fill modesFit / Fill / StretchOften one
PaddingBlurred copy or solid colorSolid bars only
Watermark / capNoneCommon
CostFree, no signupFree/limited

AnyTool is a privacy-first client-side aspect-ratio changer — reframing runs locally and nothing is uploaded.