Frequently asked questions

Yes. Your video is processed entirely in your browser. No data is sent to any server at any point. The only network request is fetching the FFmpeg WASM binary on first use.

No. alter.video has no server storage. Your file exists only in your browser's memory while you are using the tool.

No. We have no visibility into what files you process. The editor runs entirely client-side.

Two ways: right-click anywhere on the timeline bar to get a context menu and choose Cut, Speed up, or Slow down — the edit is placed at that exact time. Or scrub the playhead to where you want the edit to start and click "+ Add edit" below the cards.

Click an edit card (or its coloured band on the timeline) to make it active. Two handles appear on the timeline — drag them to resize the range. You can also type exact values in the Start/End fields on the card.

Yes. Add as many edits as you need — cuts, speed changes, and slow-downs can all coexist. They are applied together in a single FFmpeg pass when you click "Apply All Edits".

There is no hard limit enforced by alter.video, but your browser needs enough RAM to hold the file in memory. Most modern devices handle files up to a few GB comfortably.

Yes — use the video player controls to scrub through. Clicking on the timeline seeks the player to that position so you can preview where your edits will land.

It removes the portion of the video between your start and end time. The segments before and after are joined together seamlessly.

The selected segment is played at a higher speed (1.5×, 2×, 4×, 8×, or custom). Audio pitch is adjusted automatically. Everything outside the selection plays at normal speed.

The selected segment is played at a slower speed (0.75×, 0.5×, 0.25×, or custom). Audio is stretched to match. Everything outside the selection plays at normal speed.

Any value above 1.1× for speed-up, and the equivalent inverse for slow-down. Very extreme factors (e.g. 16×) are supported by chaining FFmpeg atempo filters internally. Values above 1.1 are required to produce a meaningful change.

Slightly. All operations require re-encoding with H.264 (libx264 ultrafast preset), which is high quality but not mathematically lossless. For most content the difference is imperceptible.

MP4, MKV, WebM, and MOV. MP4 is the most universally compatible format and is selected by default.

The first time you use alter.video, the browser downloads the ~30MB FFmpeg WebAssembly binary. After that it is cached by your browser and subsequent edits start immediately.

No. alter.video automatically detects if FFmpeg cannot find an audio stream and retries the edit without audio processing. You will still get a valid output video.