Slow down a video
Turn a clip into slow motion to study a swing, a dance move or a trick, without uploading it.
- Nothing is uploaded
- Works offline after first visit
- Open source
- No watermark · limit is your device’s memory; phones hold less
Slow a video down to 0.75×, 0.5× or 0.25× in your browser for slow motion. It is free, needs no account and adds no watermark, and your files are not uploaded: everything runs in your browser on your device. The size limit is your device’s memory, and phones hold less; give the page a short while after one visit to save itself for offline use, and then it works offline.
Done
Open the network tab. Your files never appear in it.
Add files and run the tool to see every request this tab makes.
Your files are processed on this device and never sent to a server. Reload the page to clear everything from memory.
Slowing a video down is how you learn a dance routine, check a golf swing, or enjoy a jump that was over in a second. Pick 0.75× for a subtle slowdown, 0.5× for half speed, or 0.25× for real slow motion.
Each frame is shown for longer and the video is encoded again in your browser. Videos filmed at 60 fps or more (most phones offer it) stay smooth when slowed; 30 fps footage looks steppier at 0.25×. The sound is slowed too, at the same pitch, or can be removed.
Nothing is uploaded, there is no watermark, and the page keeps working offline after one visit and a short wait.
How smooth the slow motion looks depends on the frames the camera recorded, because this page does not invent new ones; each frame is simply held on screen for longer. A 60 fps clip slowed to 0.5× plays at an effective 30 frames a second, which looks like ordinary video. At 0.25× it drops to 15, and you start to see each step. A 30 fps clip gives 15 frames a second at 0.5× and under 8 at 0.25×. If you know you will want a moment in slow motion, film it at 60 fps or higher.
For checking a golf swing, a tennis serve or a skateboard trick, cut the clip down to the two or three seconds around the moment with Trim video first, then slow that part to 0.25×. A 3 second swing becomes 12 seconds, long enough to pause on each position in any player. To learn a dance routine, 0.75× or 0.5× is usually enough, and because the music is stretched at the same pitch you can still count the beat. The slowed file is saved as an MP4 with the speed added to its name, such as -0_5x.
How it works
- Drop one or more videos.
- Choose how much slower (0.5× is selected).
- Press Change speed and save the MP4s.
In your browser, not on a server
Mediabunny (MPL-2.0) decodes the video in your tab and gives every frame a new time; when speeding up, frames beyond 60 a second are dropped. The sound track is decoded by your browser and stretched with WSOLA, a method that overlaps short slices of sound so the pitch stays the same. Both are encoded again by your browser (WebCodecs) into an MP4, H.264 and AAC where available.
Compared with upload-based tools: Online speed changers upload the video to process it, cap free files, and often add a watermark or turn voices into chipmunks. Here the video stays on your device and the sound keeps its pitch.
Verify it yourself. Give the page a short while after one visit to save itself for offline use, then turn off Wi-Fi or switch to airplane mode and run the tool again. Or open your browser's developer tools (F12, or Cmd-Option-I on a Mac), pick the Network tab, and watch it while you convert. The panel above does the same count for you.
Questions
Can I slow down only part of the video?
This slows the whole video. Trim video first to keep just the moment you want, then slow that clip down.
How long will my clip be after slowing it down?
Longer by the inverse of the speed: 0.75× makes it a third longer, 0.5× doubles it and 0.25× makes it four times as long. A 10 second clip becomes about 13 seconds, 20 seconds or 40 seconds. Each result lists its new length before you save it, so you can check it fits wherever you are posting it.
What does the sound sound like in slow motion?
The sound is stretched to the new length without dropping in pitch, so voices do not turn into a deep growl. At 0.75× and 0.5× speech stays understandable, just drawn out. At 0.25× it can sound smeared and echoey, because each short slice of sound has to fill four times the time. For sports clips, tick Remove the sound or add music afterwards.
Will the slowed-down video be a bigger file?
Usually, yes. The video is encoded again at a high quality setting and now runs for longer, so the file grows roughly in step with the new length: a 0.5× copy is often close to twice the size of the original. If it ends up too large to send, run it through Compress video afterwards.
Is the file uploaded anywhere?
No. There is no server in this process. The page is a static file and the work is done by code running inside your browser tab. Give the page a short while after one visit to save itself for offline use; then you can turn off Wi-Fi and it still works.
More video and audio tools
Change video speed
Make a video faster or slower, with sound that stays at the right pitch. Done on this device, never uploaded.
Compress video
Make a video a fraction of the size, or fit it under a limit like 10 MB for Discord or 25 MB for email. It is compressed on this device and never uploaded.
Video to MP4
Turn MOV, MKV and WebM files into MP4s that play everywhere. Converted on this device, never uploaded.
Trim video
Cut a clip out of a longer video without uploading it. Most cuts take seconds and keep the original quality.
Other conversions
Guides
- How to slow down or speed up a videoThis changes the saved file itself, not just how a player plays it back. Here is what actually works, including keeping the audio in tune.
- How to reverse a videoRewind effects are popular, but most phones have no reverse button. Here is where it exists, and a way to do it without installing an app.