Speed up or slow down any video
Nothing is uploaded. Your video is re-encoded inside this page, so the file never leaves your computer. Encoding runs in real time, which means it takes about as long as the finished video — speeding a clip up is quicker than the original, slow motion takes longer.
Changing a video’s speed means re-timing every frame and then re-encoding the result. This page does both in your browser: the video plays at the speed you choose, and the browser’s own video encoder records what comes out. Because it is your browser doing the work, the file is never transmitted anywhere.
The trade-off is that the encode happens in real time, so it takes about as long as the finished video. Speeding a clip up is therefore quicker than watching the original — a four-minute video at 2× is done in about two minutes — while slow motion takes longer than the source, because there is simply more finished video to write.
Audio is carried across and, by default, keeps its original pitch, so a sped-up voice stays recognisably the same voice rather than turning into a chipmunk. If you want the classic pitched-up or pitched-down effect, switch that off. You can also drop the audio entirely, which is usually what you want for a background loop or a silent demo clip.
Common uses are trimming dead time out of a screen recording, making a timelapse from a long clip, slowing a fast movement down enough to see it, and fitting a video inside a platform’s length limit. For the related audio-only job there is the Pitch and Tempo Changer, and to turn a clip into an animated image see Video to GIF.
No. The video is opened by your browser from your own disk, played back inside this page, and re-encoded by the video encoder your browser already has. Nothing is transmitted. You can watch your browser’s network tab during a conversion and see that no upload request is made at all.
Because the browser’s recorder works from the clock rather than from a queue of frames. To write a video that plays at the right speed, the page has to play the source through once at the new speed and record what comes out. That means the wait matches the length of the finished result: a clip sped up to 2× takes half the original’s running time, and a clip slowed to half speed takes twice as long.
Not unless you ask it to. By default the original pitch is preserved, so a person speaking at 2× sounds fast but still sounds like themselves. Switching to "Let the pitch change" gives the old-fashioned tape-speed effect, higher when sped up and lower when slowed down. You can also remove the audio completely.
Anything your browser can play, which in practice means MP4 with H.264, WebM, and most MOV files. MKV and some older or unusual codecs will not open, because the page relies on the browser’s own decoder rather than shipping one of its own. The result is an MP4 in Chrome, Edge and Safari, and a WebM in Firefox, which cannot write MP4 — the page tells you which one you will get before you start.
Slightly, because the video is decoded and then re-encoded rather than copied. The page encodes at a bitrate scaled to the frame size so the loss stays small and is usually invisible for normal footage. Very fine detail and heavy grain are the first things to suffer, as with any re-encode.
No fixed limit, because nothing is uploaded — but the practical limit is time and memory. The finished video is held in memory until you download it, and the encode takes as long as that finished video, so a very long slow-motion render is demanding on both counts. The page tells you the expected length before you start and warns you when it is getting long.