How to speed up a video

Choose the video above. The file card shows its length and frame rate.
Pick a speed: 1.25×, 1.5×, 2×, 3× or 4× to speed up; 0.75×, 0.5× or 0.25× to slow down.
If the video has sound, choose under "Sound": "Speed it up too, keep voice pitch" or "Remove the sound".
Press "Change the speed". With sound kept, the first run loads an audio encoder into the browser (about 30 MB), then the picture is re-encoded.
Download the MP4. The file name ends in the speed, for example "-2x".

What the new length will be

The arithmetic is simple: new length = old length ÷ speed.

1.25×: a 10-minute video becomes 8 minutes
1.5×: 10 minutes becomes 6 min 40 s
2×: 10 minutes becomes 5 minutes
4×: 10 minutes becomes 2 min 30 s
0.5×: a 20-second clip becomes 40 seconds
0.25×: a 20-second clip becomes 1 min 20 s

What happens to the picture

Speeding up squeezes the same frames into less time, which raises the frame rate. The tool caps the output at 60 frames per second and thins out frames above that.

A 30 fps video at 2× becomes 60 fps: every frame is kept, each shown for half as long.
A 30 fps video at 4×, or a 60 fps video at 2×, would need 120 fps, so every second frame is dropped to stay at 60. At that speed nobody sees the difference.

Slowing down works the other way: each frame stays on screen longer. No in-between frames are invented, so a 30 fps clip at 0.5× shows 15 different images per second and motion looks steppier than the original. Slow motion looks best when the source was recorded at a high frame rate: a 60 fps clip at 0.5× still shows 30 different images per second, which looks smooth. If your phone has a slow-motion or high-frame-rate mode, record in it when you know you'll slow the clip down.

The picture is re-encoded to MP4 (H.264 where the browser can encode it), which needs a browser with video encoding on the device: current Chrome or Edge, Safari 16.4 or later, or Firefox 130 or later on a computer.

What happens to the sound

Speed it up too, keep voice pitch: the sound is time-stretched to match, so speech is faster but not higher. This uses ffmpeg compiled to WebAssembly in your browser.
Remove the sound: the result is silent, which suits time-lapses and clips you'll put music under.

Time-stretching is a compromise. Speech stays easy to follow at 1.25× and 1.5× and is still understandable at 2×. At 3× and 4× it becomes hard to follow, and music sounds rushed. When slowing down, stretched sound can turn smeared or echoey, especially at 0.25×. For anything beyond 2× or below 0.5×, removing the sound and adding music afterwards with add audio to video usually sounds better.

Examples

Cooking or craft time-lapse

A 12-minute overhead recording at 4× with the sound removed gives a 3-minute clip; add a music track afterwards.

Software walkthrough

A 9-minute screen recording at 1.5× with the voice kept becomes 6 minutes, and the narration still sounds like the presenter, just brisker.

Sports moment

A 60 fps phone clip of a jump, first trimmed to the 4 seconds that matter, then slowed to 0.5×, gives 8 smooth seconds.

Lecture recap

A recorded class at 2× for a quick review copy; speech is fast but intelligible.

Subtitles after a speed change

Changing the speed changes every timestamp: at 2×, a line at 1:00 now belongs at 0:30. An SRT made for the original will drift further out of step the longer the video runs. Every time needs dividing by the speed, which a subtitle editor with two-point (stretch) sync can do: set the correct times for the first and last lines and it scales everything between. The guide to syncing subtitles with video explains that approach. For sped-up videos with clear speech, it can be simpler to make fresh subtitles from the new file with the subtitle generator at 1 credit per minute (minimum 5 credits per file); a 6-minute result costs 6 credits (0.6¢).

Speed is not frame rate

Changing the speed changes the length. Changing the frame rate keeps the length and only alters how many frames per second are stored. If you need a 60 fps video at 30 fps for an editor or a smaller file, change the video frame rate instead.

Limits

One speed for the whole video. For a speed ramp or a single slowed section, trim the section out first, change its speed, and join the parts in an editor.
No motion interpolation, so slow motion from 24 or 30 fps footage will look stepped.
Processing time depends on your device, the resolution and the length; keep the tab open until the download appears.
The video is processed on your device; nothing is uploaded.

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Frequently asked questions

Will my voice sound like a chipmunk at 2×?

No, if you keep the sound with the pitch-kept option: speech gets faster but stays at its normal pitch. Very high speeds still become hard to follow.

Why does my slowed-down clip look choppy?

No new frames are created, so each original frame is held longer. Footage recorded at 60 fps or more slows down much more smoothly than 24 or 30 fps.

What is the fastest speed available?

4×. At high speeds the output is capped at 60 frames per second, so some frames are dropped, which isn't visible in practice.

Can I speed up only part of a video?

Not in one pass. Trim the part out, change its speed, then join the pieces in a video editor.

Why does the first run with sound take longer to start?

Keeping the sound loads an audio encoder of about 30 MB into the browser the first time. Choosing to remove the sound skips it.

Do I need new subtitles after changing the speed?

The old timings no longer fit, because every time is divided by the speed. Stretch them with two-point sync in a subtitle editor or generate new subtitles from the new video.

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