100% browser-based · no uploads · free

alter.video

Cut, speed up, or slow down any section of your video.
Your file never leaves your device.

Drop your video here

or click to browse — MP4, MKV, MOV, WebM, AVI and more

Powered by FFmpeg WebAssembly — runs entirely in your browser

How it works

Three steps. No account. No waiting.

01

Drop your video

Drag and drop any video file — MP4, MKV, MOV, WebM, AVI. It loads instantly in your browser.

02

Add edits on the timeline

Right-click anywhere on the timeline to add a Cut, Speed up, or Slow down edit at that exact point. Or move the playhead and click "+ Add edit". Stack as many edits as you like.

03

Download the result

FFmpeg applies your edit entirely in your browser. Download the modified video when it finishes.

Three operations

Pick any section of your video and apply one of three edits.

Cut

Delete a section

Select a start and end time, then remove that segment entirely. The video before and after the selection are seamlessly joined together.

Useful for cutting out mistakes, silences, or unwanted parts.

Fast

Speed up a section

Choose a segment and apply a speed multiplier (1.5×, 2×, 4×, or custom). The selected portion plays faster while the rest stays at normal speed.

Great for time-lapses or skipping through slow sections.

Slow

Slow down a section

Apply a slow-motion effect to any segment of your video. Choose 0.75×, 0.5×, 0.25×, or a custom factor.

Perfect for highlighting a moment or creating a dramatic effect.

Why alter.video

Everything runs in your browser. Your file never touches a server.

Zero privacy risk

Your video is never sent to any server. FFmpeg runs entirely in your browser via WebAssembly.

No account needed

Open the page, edit, download. No sign-up, no email, no billing.

All major formats

Output to MP4, MKV, WebM, or MOV. Input accepts virtually any video format.

Precise selection

Drag timeline handles or type exact second values for frame-accurate edits.

Truly free

No watermarks, no file size limits (within your device's RAM), no paid tiers.

Powered by FFmpeg

The world's most trusted video processing tool — compiled to WebAssembly and running locally.

Common questions

Quick answers to the most asked questions.

Is my video safe?

Yes. Your video is processed entirely in your browser. No data is sent to any server at any point.

Can I apply multiple edits?

Yes — add as many edits as you like (cuts, speed changes, slow-downs) and apply them all in a single pass. Right-click the timeline to quickly add an edit at any point.

Why does the first edit take longer to start?

The first time, the browser downloads ~30MB of the FFmpeg WebAssembly binary. It is cached afterwards, so subsequent runs start instantly.

Will the quality drop?

Slightly. Speed and slow-down operations require re-encoding with H.264 (libx264 ultrafast), which is high quality but not lossless. Delete operations also re-encode for the same reason.

View all FAQs