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

How do I resize or scale a video in my browser without uploading it?

Open AnyTool's Video Resize, drop in a clip, and pick a resolution preset (4K, 1440p, 1080p, 720p, 480p or 360p), a percentage scale, or a custom Width×Height with aspect-lock, plus a fit/fill/stretch mode. It re-encodes to a real H.264 MP4 (or VP8 WebM) with even dimensions using a self-hosted ffmpeg engine right in your browser. The video is never uploaded, the engine core is bundled (no CDN), and there is no watermark or size cap.

  • Presets (4K/1440p/1080p/720p/480p/360p), % scale or custom W×H with aspect-lock
  • Fit, fill or stretch modes; even-dimension H.264 MP4 or VP8 WebM output
  • Self-hosted ffmpeg engine — no CDN, no upload
  • 100% in your browser — no signup, no watermark, no cap

What is

Video resizing

Video resizing changes a clip's pixel resolution — scaling it up or, more commonly, down to a smaller frame — and re-encodes the result. Resizing can target a preset resolution, a percentage of the original, or a custom width and height (optionally aspect-locked), with fit/fill/stretch controlling how the source maps into the new frame. Client-side resizing runs the encoder in the browser, so the file is never uploaded.

Video Tools

Related terms

resolutionaspect ratioH.264downscaleffmpeg

How to Resize a Video

Scale a video to a new resolution in your browser.

30 secWeb browser
  1. 1

    Add a video

    Drop in an MP4, WebM, MOV, MKV or AVI — it stays on your device.

  2. 2

    Choose a size

    Pick a resolution preset, a percentage, or a custom Width×Height with a fit mode.

  3. 3

    Export

    Resize and download an MP4 or WebM — nothing is uploaded.

Result: A resized video file

Frequently Asked Questions

No — it is rescaled and re-encoded entirely in your browser with a self-hosted engine.

The file never leaves your device and there is no size cap, signup or watermark, unlike most online resizers.

Both — use a preset or percentage to keep the ratio, or enter a custom Width×Height with aspect-lock on or off.

Fit, fill and stretch modes control how the frame is handled, and dimensions are rounded to even numbers so H.264 always encodes.

Yes — it produces a real H.264 MP4, or a VP8 WebM if you prefer.

That is an edge over in-browser rivals that are WebM-only or offer no resolution presets.

Detailed Explanation

Methodology

How the Video Resizer Works

AnyTool resizes video 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. You choose a target size by resolution preset, percentage, or a custom W×H with an optional aspect lock, and pick a fit mode: fit letterboxes with scale + pad, fill (cover) uses scale + crop, and stretch scales directly. Dimensions are snapped to even integers so yuv420p encoding stays valid. The clip is written to ffmpeg's virtual filesystem (MEMFS), processed with the scale filter, and read back as a blob — a real H.264 MP4 (-pix_fmt yuv420p, +faststart, AAC audio) or a VP8 WebM. Single-threaded is deliberate: the multi-threaded core needs SharedArrayBuffer + cross-origin isolation (COOP/COEP), which would block cross-origin ad iframes.

  • Runs client-side — the video is never uploaded
  • Self-hosted ffmpeg core (bundled) — no CDN
  • Presets, percentage, or custom W×H with aspect lock
  • Fit (scale+pad), fill (scale+crop), or stretch
  • Even-dimension snap for valid yuv420p
  • Real H.264 MP4 (+faststart, AAC) or VP8 WebM output
Privacy & Security

Privacy & Output vs Upload-based Resizers

Most online resizers upload your file and many in-browser rivals can only emit WebM via the MediaRecorder API. AnyTool resizes locally and encodes a real, broadly-compatible H.264 MP4 (or VP8 WebM if you prefer), so the video never leaves your browser, there is no size cap or watermark, and it works offline after the first load.

Video resizing: AnyTool vs typical tools
CapabilityAnyToolTypical tools
Data handlingIn your browserOften uploaded
Output formatReal H.264 MP4 / WebMWebM-only in-browser
Fit modesFit / fill / stretchVaries
Watermark / capNoneCommon
CostFree, no signupFree/limited

AnyTool is a privacy-first client-side resizer — scaling runs locally and nothing is uploaded.