Guide
How to speed up or slow down a video
To change a video's speed, every frame's timestamp is scaled, so 2× plays twice as fast and 0.5× half as fast. To keep voices natural, the audio needs a time-stretch that changes tempo without changing pitch. Smooth slow motion requires footage recorded at a high frame rate; slowing normal 30 fps footage makes motion choppy.
Use change video speed to go from 0.25× to 4× with pitch-preserved audio, in your browser. For audio files, use change audio speed.
How to change video speed with Videozify
- Open Change video speed and drop in your clip.
- Pick a speed: 1.25× or 1.5× to tighten a tutorial, 2×–4× for a timelapse, 0.5× for slow motion.
- Press Change speed and wait for the progress bar.
- Preview the result. For even faster timelapses, run it again (4× twice is 16×).
- Download the MP4.
Why audio sounds like a chipmunk
Simply playing audio faster raises its pitch, like a record at the wrong speed. A time-stretch algorithm, such as FFmpeg's atempo, changes the tempo while keeping the pitch, so a 1.5× tutorial still sounds like the same person, just faster. Extreme speeds (above 2×) start to sound artificial, and timelapses usually drop or replace the audio anyway.
Slow motion and frame rate
Slow motion looks smooth only when there are enough frames. A clip recorded at 120 fps and played at 30 fps is 4× slow motion with every frame unique. Slowing a 30 fps clip to 0.25× shows each frame four times, which stutters. Phones have dedicated slow-motion modes (120 or 240 fps) for exactly this reason.
Frame interpolation (motion smoothing) can invent in-between frames, but it creates warping artefacts on fast motion and needs specialised software.
- 0.5×: fine from 60 fps footage
- 0.25×: needs 120 fps footage
- 0.125×: needs 240 fps footage
Speeding up: timelapse and hyperlapse
For a process that takes hours, such as a sunset, a drawing or a build, a phone's built-in Time-lapse mode records frames at intervals and produces a much smaller file than recording normally and speeding it up later. For footage you already have, 4× to 16× speed works well. Speeding up also shrinks the file, because there are fewer seconds of video.
Native options
iPhone: slow-motion videos recorded in the Camera app can be edited in Photos. Tap Edit and drag the vertical lines in the timeline to choose which part plays slowly. iMovie for iOS can change the speed of any clip.
Android: Google Photos doesn't change speed for normal clips, but many gallery apps (Samsung, Xiaomi) and the camera's slow-motion editor do.
Windows: Clipchamp has a speed control for clips on the timeline. Mac: iMovie and QuickTime Player can't set arbitrary speeds directly; iMovie's speedometer button can.
Making tutorials easier to watch
Screen recordings often include typing, loading and waiting. Speeding those sections to 2–4× while keeping explanations at normal speed makes a tutorial far more watchable. Split the video at the slow parts, speed those up, then merge everything back together.
Speed and music
When you speed up a clip that has background music, the music gets faster too. Even with pitch preserved, music at 1.5× sounds unnatural. For montages, it's usually better to mute the clip after changing speed and add music at normal speed in an editor, or choose music with a tempo that matches the new pace.
Variable frame rate recordings
Screen recordings and some phone videos use a variable frame rate, so the time between frames changes. Speed changes still work, but very high speeds can look uneven when the original was recorded at a low, inconsistent rate. Converting to a constant 30 fps while changing speed, which Videozify does, gives smoother results.
Combining speed with other edits
The order of edits matters. Trim first, so you don't process footage you'll throw away. Change speed next. Add captions after the speed change, so they're timed to the final video; captions created before a speed change will be out of sync. Compress last if the file needs to fit a size limit.
Popular speed effects
- Timelapse: 4×–16× for sunsets, drawing and cooking
- Fast tutorial: 1.25×–1.5× for screen recordings
- Dramatic slow motion: 0.5× from 60 fps footage
- Super slow motion: 0.25× from 120 fps footage
- Speed ramp: split, change speed on one section, merge
File size and quality after a speed change
Speeding up a video shortens it, so the file usually gets smaller in proportion: a 2× video is about half the size at the same quality. Slowing down lengthens it and increases the size. The video is re-encoded once at high quality, and audio is time-stretched with pitch preserved, so voices stay natural. For best results, change speed from the original recording rather than from an already-compressed copy, since each re-encode costs a little detail.
Speed changes on Chromebook and Linux
ChromeOS's built-in Gallery app can't change speed, but Videozify works in Chrome. On Linux, Shotcut and Kdenlive include speed controls with pitch correction, and ffmpeg can combine the setpts and atempo filters on the command line. Browser-based processing avoids installing anything and keeps the video on your device.
How it works under the hood
Videozify uses FFmpeg compiled to WebAssembly. The setpts filter rescales each frame's timestamp to change playback speed, and the atempo filter stretches audio without changing pitch, chained for speeds beyond its 0.5–2× range. Everything runs in your browser tab, so the video is never uploaded, which suits personal and work footage alike.
Social video speed tips
Slightly faster playback, 1.1× to 1.2×, can make vlogs and talking-head clips feel more energetic without viewers noticing. For dramatic moments, 0.5× slow motion from 60 fps footage is the most common choice.
Frequently asked questions
Will speeding up a video change the voice pitch?
- Not with Videozify; pitch is preserved.
Why is my slow motion choppy?
- The source doesn't have enough frames. Record at 60–240 fps for slow motion.
What's the maximum speed?
- 4× per pass. Repeat for faster speeds.
Does a sped-up video get smaller?
- Yes. It's shorter, so it uses fewer bytes.
Is my video uploaded?
- No. Processing runs in your browser.
Can I speed up just part of a video?
- Split the part out, change its speed, then merge it back.
Will a sped-up video lose quality?
- It's re-encoded once at high quality, so the picture looks the same; only the playback speed changes.
Can I make a slow-motion GIF?
- Yes. Slow the clip down first, then convert the result with Video to GIF.
Can I make a timelapse from a normal video?
- Yes. Speed it up 4× or more; repeat for higher speeds.
Does speed change affect captions?
- Yes. Generate captions after changing speed.
Can I speed up a video on my phone?
- Yes. Videozify works in mobile Chrome and Safari for short clips.
What's the slowest speed?
- 0.25×, a quarter of normal speed.
Can I reverse and speed up together?
- Yes. Reverse the clip first, then change its speed.
Is there a watermark?
- No. Videozify never adds a watermark.
Does speed change work on MKV or MOV?
- Yes. Common video formats are supported, and the output is MP4.
Can I slow down audio only?
- Use the change audio speed tool for audio files.