What does changing a video's speed do?
Video is a sequence of frames, each with a timestamp. Speeding up by 2× halves every timestamp, so each frame is shown for half as long and the whole video lasts half the time. Slowing down to 0.5× doubles them. No frames are added or removed; they're just shown faster or slower.
Sound is harder. Simply playing audio faster raises its pitch, the 'chipmunk' effect, and slowing it lowers it. This tool uses time-stretching instead, which changes the tempo while keeping the pitch, so voices stay natural at 1.5× and music stays in key at 0.75×.
Which speed should I pick?
Different speeds suit different kinds of video:
- 1.5× and 2×: the sweet spot for lectures, tutorials, meetings and talking-head videos. Speech stays easy to follow and you save a third to a half of the time.
- 3× and 4×: for time-lapse-style sequences such as cooking, crafts, drawing, cleaning, travel or setting up, where the process matters more than each moment.
- 0.75×: a gentle slow-down for following dance moves, sports technique or fast instructions.
- 0.5× and 0.25×: slow motion for dramatic moments, such as splashes, jumps and sports highlights.
Getting smooth slow motion
Slow motion looks smooth only if there are enough frames to spread out. A 30 fps video at 0.5× plays at an effective 15 fps, which looks slightly choppy, and at 0.25× it's 7.5 fps, clearly stuttering. A 60 fps video at 0.5× still plays at 30 fps, which looks smooth.
For real slow motion, record at a high frame rate. iPhones and most Android phones offer 120 or 240 fps slow-motion modes, and many can record ordinary video at 60 fps (on iPhone, Settings → Camera → Record Video). Slowing those down keeps motion fluid.
How long the result is
The new length is the original length divided by the speed. A 60-second video lasts 30 seconds at 2×, 15 seconds at 4× and 4 minutes at 0.25×. Speeding up is a handy way to fit a longer clip under a platform's time limit, for example squeezing a 90-second clip into a 60-second Story.
File size follows length roughly: faster videos are smaller and slow-motion videos are bigger.
Quality, sound and privacy
The video is re-encoded to H.264 MP4 at high quality (CRF 23) and the audio to AAC at 192 kbps. Videos without sound simply come out silent. At extreme settings like 4× or 0.25× the time-stretched sound becomes noticeably processed, which is unavoidable; for those, many people mute the result and add music instead.
Everything runs inside your browser. The video isn't uploaded, nothing is stored, and no watermark is added.
Speed in the app vs speed in the file
TikTok, Instagram and CapCut let you change speed while editing inside the app, but that only applies to what you post there. If the sped-up or slowed-down clip needs to go somewhere else, such as a different platform, a presentation or a message, you need the speed baked into the file, which is what this tool produces.
For very long processes, think about time-lapse at recording time. The Time-lapse mode on iPhones and most Android phones captures frames at intervals while you film, so an hour becomes about 20–40 seconds of smooth video. Speeding up a normal recording by 4× is better for processes of a few minutes, where you still want to see the details.