Change Video Speed Online
Speed up a time-lapse, slow down a replay, or adjust any clip in your browser. Fast mode changes timing without re-encoding, keeping picture quality identical. Re-encode mode creates a compatible H.264 MP4, with pitch-corrected audio in both modes.
Changing speed sounds simple until your clip has speech, music, or sync-sensitive audio. If you only make the video play faster, your voice can sound squeaky. If you only touch the video track, audio and video can drift apart.
That is why GrepCut treats timing and audio together. When you change the speed of the clip, the audio duration changes too, and pitch correction helps speech stay natural instead of turning into a chipmunk effect.
You can use this when your tutorial has long pauses, your screen recording needs tighter pacing, your reaction shot needs slow motion, or your process clip needs a quick time-lapse feel.
In Fast mode, GrepCut does not rebuild the picture frame by frame. It copies the compressed video stream and changes the timing so the same frames play slower or faster.
That keeps visual quality identical to the source video stream because the video data is copied instead of decoded and encoded again. The export can also finish much faster than a full render, especially when your device can avoid heavy video encoding work.
The audio still has to be rebuilt because its duration changes with the speed you choose. GrepCut time-stretches the audio and keeps pitch corrected automatically.
A file extension does not tell the whole story. Your file might be MP4, MOV, WebM, MKV, or M4V, but the codec inside can still decide whether a device, browser, social uploader, or editor accepts it.
Re-encode mode fully renders the result to H.264 MP4. It takes longer because every frame is encoded again, but it gives you an output that is easier to open, send, and upload across everyday apps.
Use Re-encode when compatibility matters more than preserving the exact source video stream. Use Fast mode when you want speed and copied-video quality.
Can you change video speed without uploading the file?
Yes. GrepCut processes your video locally in your browser, so your file stays on your device instead of being uploaded to a server.
Will changing speed lower your video quality?
In Fast mode, the video stream is copied and only the timing changes, so the visual quality stays identical to the source video stream. In Re-encode mode, the video is compressed again to create a more compatible H.264 MP4.
Why is Fast mode quicker than a normal video export?
Fast mode skips the slowest part of a full render. It does not decode and re-encode every video frame. It copies the original compressed video stream and adjusts when those frames play.
Will your audio sound higher or lower after the speed change?
GrepCut corrects pitch automatically while changing audio duration. That helps speech stay natural instead of squeaky when sped up or too deep when slowed down.
Should you pick Fast mode or Re-encode mode?
Pick **Fast mode** when you want the quickest export and no extra visual compression. Pick **Re-encode mode** when a device, social uploader, or editor rejects your file, or when you need a broadly compatible MP4.
Can you speed up only one part of the video?
This tool changes the speed of the whole clip. If you need to speed up one section, slow another section down, or create a ramp, open the file in [GrepCut Studio](/) and edit it on the timeline.
What video formats can you use?
You can add MP4, MOV, WebM, MKV, M4V, and other common video files. The downloaded result is an MP4.
Can changing speed make your file smaller?
Not reliably. In Fast mode, the file size usually stays close to the source because the video data is copied. If you need a smaller export or a more compatible file, use Re-encode mode.