Change a video's speed
Choose an MP4 or MOV, pick a speed from 0.25× (four times slower) to 4× (four times faster) and download a new MP4. The sound is removed by default, because played faster or slower it changes pitch; you can keep it anyway if you want that effect.
Checking what your browser can do…
How it works
- •Choose or drop a video. The preview plays at the speed you pick.
- •Pick the speed, then choose what happens to the sound.
- •Press Change speed. Every frame gets a new time. When speeding up, frames are skipped so the result keeps the original frame rate; when slowing down, the existing frames are spread out. The picture is re-encoded as H.264.
- •If you keep the sound, it is decoded, stretched or squeezed to the new length, and re-encoded as AAC.
- •The file is read with mp4box.js and written with mp4-muxer, two open-source libraries served from this site (licences: /tools/vendor/NOTICE-media.txt). Decoding and encoding use your browser's own WebCodecs; nothing is sent anywhere.
What it does and what it cannot do
- •Reads MP4, MOV and M4V up to 1 GB with H.264 video (HEVC from phones only where your browser can decode it). WebM, MKV and AVI are not supported.
- •Needs a browser with WebCodecs and an H.264 encoder: recent Chrome or Edge on a computer, Safari 16.4 or later, or Firefox 130 or later. The page checks first and says so if yours cannot.
- •Kept sound changes pitch with the speed (higher when faster, deeper when slower). This tool has no pitch correction, so it says so and removes the sound unless you choose to keep it.
- •Slow motion does not invent frames: 0.5× of a 30 fps video plays at 15 fps and 0.25× at 7.5 fps, which looks jumpy. Footage shot at 120 or 240 fps slows down smoothly.
- •One speed for the whole video. Speed ramps and speeding up only part of a clip are not possible here.
- •The picture is re-encoded, so a little quality is lost. Metadata such as date and location is not copied.
Questions
- Is my video uploaded?
- No. Your browser re-times and saves the video itself; nothing is sent anywhere.
- Why is the sound removed?
- Played faster or slower, sound changes pitch: voices sound squeaky or deep. That is rarely wanted, so it is removed unless you choose "Keep the sound at the new speed".
- How do I make a time-lapse?
- Pick 4×. For a stronger effect, run the result through the page again: 4× twice is 16×.
- Why does slow motion look jumpy?
- The page only has the frames that were recorded. A 30 fps video at 0.25× shows 7.5 frames per second. For smooth slow motion, record at 120 or 240 fps on your phone first.
- Will the new video be smaller?
- A faster video is shorter, so usually yes. A slower one is longer and usually bigger.
- Can I change speed for only part of the video?
- Not here: one speed applies to the whole file. Trim the part out first, change its speed, then join the pieces with another tool.