Change Video Speed Online

Speed up or slow down a clip

Changing playback speed is useful for many small editing tasks. You can speed up a screen recording to keep a tutorial moving, slow down a sports clip to study motion, shorten a product demo or create a slightly faster social version of a longer take. This tool creates a new MP4 at the chosen speed factor instead of relying on a player setting, so the downloaded file keeps the timing change wherever it is opened.

The work happens in your browser. The source video is loaded into ffmpeg.wasm only after you press the button, processed with video and audio timing filters and downloaded directly. Your file is not sent to a server, which is important for work recordings, private clips, unreleased demos and any media that should stay on your own device.

How the speed factor works

A value below 1 slows the video down. For example, 0.5x makes the result twice as long. A value above 1 speeds it up, so 2x makes the result roughly half as long. The video timing uses ffmpeg's setpts filter, while the audio uses atempo to match the new duration. The supported range is 0.5x to 2x because that range is reliable for a single audio tempo filter.

Quality and review tips

Timing changes require re-encoding, so processing time depends on duration, resolution and your device. The first run may pause while the WebAssembly engine downloads, but later runs in the same tab can reuse it. Check the downloaded file for sync and smoothness before sharing it. If a clip has no audio track, the tool can still produce a video-only speed change when the audio pass is not applicable.

Worked example and limits

Suppose you have a 10-minute screen recording and choose 1.5x. The video timestamps are divided by 1.5, so the result lasts about 6 minutes 40 seconds, and the audio is sped up by the same factor. Choose 0.5x on a 30-second clip and you get a 60-second slow-motion version. Nothing is interpolated: slowing down stretches existing frames, so fast motion can look choppy rather than smooth.

Because atempo changes tempo without lowering or raising pitch in the usual way a record speed change would, speech at 1.5x remains understandable, though it can sound slightly processed at the extremes. The output is H.264 video at CRF 23 with AAC audio at 160 kbps, packaged as MP4 with the index at the start so it can begin playing quickly on the web. For speeds beyond 2x or below 0.5x, run the tool twice on its own output.