The short answer
Open the video in the speed tool below. Under Speed choose 0.25×, 0.5× or 0.75× to slow it down, or 1.25×, 1.5×, 2×, 3× or 4× to speed it up. Under Sound choose Keep, natural pitch, Keep, pitch changes or Remove. The preview plays at the chosen speed, and the line under the options shows the new length and whether the picture is copied or encoded again. Press Change speed, check the result and download it.
The result keeps the format of the original: an MP4 stays MP4, a WebM stays WebM. MP4, MOV, WebM and MKV files are supported, and nothing is uploaded, because the whole job runs on your device.
Try it here: Video Speed Changer
Open the full tool pageWhich speed to choose
The new length is simply the old length divided by the speed. A 3 minute video at 2× lasts 1 minute 30 seconds; at 0.5× it lasts 6 minutes. The table gives typical uses for each speed.
If you need to fit a clip into a length limit, divide the current length by the limit and take the next speed up. A 90 second clip for a 60 second limit needs 1.5×; a 2 minute clip for a 60 second limit needs 2×.
| Speed | New length of a 60 s clip | Typical use |
|---|---|---|
| 0.25× | 4 min | A single moment: a splash, a jump, a ball being hit |
| 0.5× | 2 min | Classic slow motion for sports and dance |
| 0.75× | 80 s | Following fast talkers or quick hand movements |
| 1.25× | 48 s | Tightening a lecture or a talking head video |
| 1.5× | 40 s | Screen recordings, tutorials, fitting a time limit |
| 2× | 30 s | Cooking, walkthroughs, long demonstrations |
| 3× and 4× | 20 s and 15 s | Time lapse of painting, building, cleaning |
Why the picture usually keeps its quality
Every frame in a video file has a time stamp that says when it should appear. Changing the speed only needs new time stamps: the frames themselves are copied as they are. That is why the tool is quick even for long videos and why each frame looks exactly like the original. In tests, a 30 fps video at 2× became a 60 fps video with every frame kept and no re-encoding.
The limit is about 60 frames per second in the result. A 30 fps video at 4× would need 120 frames per second, which most screens and players cannot show anyway. In that case the tool drops the extra frames and encodes the picture again at 30 fps, so the file stays smooth and plays everywhere. The note under the options tells you before you save: The picture is copied without re-encoding, or that extra frames are dropped and the picture is encoded again. The finished result is marked No quality loss or Re-encoded.
What happens to the sound
When sound is played faster, its pitch rises; played slower, it drops. That is the familiar chipmunk voice at 2× and the deep, slurred voice in slow motion. The Sound option gives you three choices.
Keep, natural pitch cuts the sound into very short pieces and puts them back together at the new speed, choosing each piece so the waves line up. In our tests a 440 Hz tone stayed at 440 Hz at every speed from 0.25× to 4×, so speech stays clear and music stays in its key. At the extremes a slight echo or roughness can be heard, which is normal for this method. Keep, pitch changes works like a tape or a record: at 0.25× the same 440 Hz tone became 110 Hz, two octaves lower. Remove leaves the video silent.
- Talks, lessons, tutorials: Keep, natural pitch
- Funny effect, retro tape feel: Keep, pitch changes
- Time lapse and slow motion clips: Remove, then add music if you like
- Background noise you do not want: Remove
Getting smooth slow motion
Slowing down spreads the same frames over a longer time. A 30 fps video at 0.5× plays at 15 frames per second, and at 0.25× at only 7.5, which looks like a series of photos. The tool does not invent frames in between, so the smoothness depends on the original recording.
If you plan to slow a scene down, record it at 60 fps or in your phone's slow motion mode, which often records at 120 or 240 fps. A 120 fps clip at 0.25× still plays at 30 frames per second and looks completely smooth. For videos you already have, 0.5× or 0.75× usually looks better than 0.25×.
Changing speed with built in apps
iMovie on iPhone, iPad and Mac has a speed control for each clip, and Clipchamp on Windows can speed clips up or slow them down. Phones that record slow motion also let you choose which part of a slow motion clip plays slowly in the gallery app. These editors usually save by encoding the whole video again.
The browser tool is useful when you only want to change the speed of a whole file, want to keep the picture untouched, or work with WebM and MKV files that some editors do not open. To change the speed of just one part, cut that part out first with a video trimmer and then change its speed.
Common problems and fixes
- Your browser cannot create this format: Firefox cannot encode AAC sound, which MP4 and MOV need. Use Chrome, Edge or Safari, or choose Remove for the sound.
- Slow motion looks jerky: the original has too few frames per second. Use a gentler speed such as 0.5× or record at a higher frame rate.
- The sound has a slight echo at 0.25× or 4×: this is the limit of pitch keeping at extreme speeds. Try a speed closer to 1×, or Remove the sound and add music.
- The video is too long to process in the browser: cut it into shorter parts first, change their speed, then join them.
- The file cannot be read: some codecs, such as HEVC from iPhones, are not decoded by every browser. Try Chrome, Edge or Safari, or convert the video to MP4 first.