What does changing video speed do?

Changing the speed of a video makes it play faster or slower as a new file, instead of only in your player. Speeding up turns a long recording into a quick time-lapse or a tutorial into something easier to skim. Slowing down shows details in fast movement, like a sports move or a pet jumping. The length of the video changes with the speed: at 2× a one-minute clip lasts 30 seconds, at 0.5× it lasts two minutes.

Tool description

This tool changes the speed of a video in your browser, from 0.1× (ten times slower) to 16× (sixteen times faster). Choose a video, set the speed with the slider or type it, and download the new video as an MP4. The original and new lengths are shown as you change the speed. Nothing is uploaded: the video is processed on your device with FFmpeg compiled to WebAssembly.

Features

  • Any speed from 0.1× to 16× in steps of 0.05, or type an exact value
  • The sound is sped up or slowed down with it, keeping its normal pitch
  • Turn off Keep audio to make a silent video
  • The preview plays at the chosen speed, so you can check it before saving
  • Shows the original and new length before you start
  • Saves as MP4 with H.264 video and AAC audio, which plays almost everywhere
  • Shows the output file size and a preview before you download

How it works

FFmpeg changes the timestamp of every frame, so at 2× each frame is shown for half as long, and encodes the video again. The audio goes through FFmpeg's atempo filter, which stretches or squeezes the sound without making voices sound higher or lower. For speeds beyond 2× or below 0.5×, several atempo filters are chained together.

Tips

  • Slowing a video down doesn't add frames, so slow motion looks smoothest from videos recorded at a high frame rate, such as 60 or 120 frames per second.
  • Voices are hard to follow above about 2×. For a time-lapse, turn off Keep audio.
  • To play a video faster only while you watch, use your player's playback speed instead. This tool is for saving a new file.
  • The first run downloads FFmpeg, about 30 MB. Later runs on the same page start right away.