Change video speed

What changes when you change the speed

A video is a series of frames, each with a time stamp. Speeding it up moves every frame earlier, so the same frames play in less time; slowing it down spreads them out. The picture itself is not redrawn, only retimed and then encoded again. At 2x a 10 minute video lasts 5 minutes; at 0.5x it lasts 20.

• Faster suits tutorials, screen recordings and long walk throughs, where viewers want the information without the waiting. 1.5x keeps speech easy to follow; 2x is still understandable for most people.
• Slower suits sports, dance and anything with fast movement worth studying. 0.5x and 0.25x stretch a moment out.
• Time lapse style: 3x or 4x turns a long, slow scene, such as clouds or a busy street, into a quick summary.

Frames when speeding up

Playing a 30 frames per second video at 4x would mean 120 frames per second, more than screens and players can show. So when speeding up, the tool drops frames that would come less than a sixtieth of a second apart, keeping at most 60 frames per second. Motion stays smooth and the file does not carry frames nobody would see. When slowing down, every frame is kept and shown for longer, so slow motion from a normal camera looks a little steppy; true smooth slow motion needs footage shot at a high frame rate.

Keeping voices natural

Played faster, sound normally rises in pitch, the chipmunk effect; played slower, it drops, like a slow tape. Keep the original pitch, on by default, stretches or squeezes the sound in time without changing its pitch, using WSOLA, a method that cuts the sound into short overlapping pieces and fits them together where their waves match. Voices sound like the same person speaking faster or slower. Switch it off if you want the effect.

Sound is re-timed in memory, which allows files up to 45 minutes of audio. For longer videos, trim them first with trim video, or choose Remove the audio if the sound does not matter.

Size of the result

The video is encoded again with your device's encoder, so the result is a fresh file whose size follows its new length: shorter when sped up, longer when slowed down. To bring it under a size limit afterwards, use compress video.

If something goes wrong

• It says the audio is longer than 45 minutes. Trim the video, or remove the audio.
• Slow motion looks jerky. The video was not shot at a high frame rate, so there are no extra frames to show. Use a gentler slow down such as 0.75x.
• It says the video cannot be re-timed in the chosen container. Choose MP4 as the output.
• The browser says it cannot do this. The tool needs WebCodecs, which Chrome, Edge, Safari 16.4 or newer and Firefox 130 or newer provide.