Ijharul Islam
To slow down a video, open it in a tool with a speed setting, choose a speed below 1× such as 0.5× or 0.25×, and save a new copy. Whether it looks smooth depends on how it was recorded: slowing a 30 fps clip to half speed shows each frame twice and looks choppy, while a 60 fps clip at half speed still plays 30 new frames a second. Record at 60 fps for half speed and 120 fps or more for quarter speed.
More on this topic: Video editing how-tos, every guide in one place.
Below: how to slow a video in your browser, on a phone and with FFmpeg, a frame-rate table for smooth slow motion, and fixes for footage you can't re-record.
The short answer
In your browser, QuickVeed's free Video Speed Changer slows a video to 0.75×, 0.5× or 0.25× and saves a new file. On Android, Google Photos offers ½× and ¼×; on iPhone, slow-motion clips have a speed control in Photos. With FFmpeg: ffmpeg -i in.mp4 -filter:v "setpts=2*PTS" -filter:a "atempo=0.5" out.mp4 for half speed. For smooth results, the recorded frame rate × the speed should be at least 24-30 fps.
Key takeaways
- New length = original length ÷ speed: 10 seconds at 0.5× lasts 20 seconds; at 0.25×, 40.
- Smooth slow motion needs recorded fps × speed ≥ your playback rate (24-30 fps).
- 60 fps → 0.5×, 120 fps → 0.25×, 240 fps → about 0.125×.
- Slowing 24 or 30 fps footage repeats frames; frame blending or optical flow can smooth it, with artefacts.
- Slowed speech sounds odd; slow only action shots or mute and add music.
How do you slow down a video for free?
You slow down a video for free with QuickVeed's video speed changer, which is free, runs in your browser and never uploads your file:
- Open the tool and drop an MP4 or WebM file, up to 500 MB.
- Pick 0.75×, 0.5× or 0.25×.
- Press play to preview. Keep voice pitch is on by default, so voices don't drop to a growl; untick it for a deep slow-motion effect.
- Check the new length the tool shows, then click Save at this speed. The result can be up to 20 minutes long.
The browser plays the video at the new speed and records it, so saving takes as long as the slowed video: a 30-second clip at 0.5× takes a minute. Output is up to 30 fps, which suits slow motion from 60 or 120 fps footage. The file is MP4 where your browser can record MP4 and WebM otherwise. Need only one moment in slow motion? Cut it out first with the free video trimmer, slow it, then join the pieces with the free video merger.
What frame rate do you need for smooth slow motion?
For smooth slow motion, you need to record at a frame rate high enough that, after slowing, there are still at least 24 to 30 different frames each second. The rule: recorded fps × speed = frames per second you'll see.
| Recorded at | 0.5× | 0.25× | 0.125× |
|---|---|---|---|
| 24 fps | 12 fps (choppy) | 6 fps (very choppy) | 3 fps |
| 30 fps | 15 fps (choppy) | 7.5 fps | 3.75 fps |
| 60 fps | 30 fps (smooth) | 15 fps (choppy) | 7.5 fps |
| 120 fps | 60 fps (smooth) | 30 fps (smooth) | 15 fps |
| 240 fps | 120 fps | 60 fps (smooth) | 30 fps (smooth) |
Many phones have a slow-motion mode that records at 120 or 240 fps; check your camera's settings for the exact options. For 24 fps films, the same logic applies: 48 fps footage plays smoothly at half speed on a 24 fps timeline. 24 vs 30 vs 60 fps covers choosing a frame rate in general.
How long will the slowed video be?
The slowed video's length is the original length divided by the speed. Here's a quick table:
| Original | 0.75× | 0.5× | 0.25× |
|---|---|---|---|
| 5 seconds | 6.7 s | 10 s | 20 s |
| 10 seconds | 13.3 s | 20 s | 40 s |
| 30 seconds | 40 s | 1 min | 2 min |
| 1 minute | 1 min 20 s | 2 min | 4 min |
Watch platform limits: a 50-second clip at 0.25× becomes 3 min 20 s, past the 3-minute limit for Shorts. For several clips, the free video duration calculator adds up lengths. Going the other way is in how to speed up a video, and how long a video is at 1.25×, 1.5× or 2× has watch-time tables.
How do you slow down a video on iPhone or Android?
On a phone, use the gallery app's speed control or a slow-motion recording:
- iPhone: record in Slo-mo mode. In Photos, edit the clip and drag the slow-motion markers to choose which part plays slowly. Apple's help also describes a Speed control in Photos for videos recorded at more than 30 fps, in iOS 18 and later.
- Android: Google's help for editing videos in Google Photos lists speed options including ¼× and ½× to slow down; save a copy afterwards. Options can vary by phone and app version. Many Android camera apps also have a Slow motion mode.
- Any phone: open the free video speed changer in your mobile browser.
How do you slow down a video with FFmpeg?
FFmpeg slows the picture with the setpts filter and the sound with atempo. setpts multiplies timestamps by 1 ÷ speed (2 for half speed); atempo takes the speed itself and keeps the pitch.
| Job | Command |
|---|---|
| Half speed with sound | ffmpeg -i in.mp4 -filter:v "setpts=2*PTS" -filter:a "atempo=0.5" out.mp4 |
| Quarter speed with sound | ffmpeg -i in.mp4 -filter:v "setpts=4*PTS" -filter:a "atempo=0.5,atempo=0.5" out.mp4 |
| 120 fps clip to smooth 30 fps slow motion (no sound) | ffmpeg -i in.mp4 -filter:v "setpts=4*PTS" -r 30 -an out.mp4 |
| Smooth a 30 fps clip with motion interpolation | ffmpeg -i in.mp4 -filter:v "setpts=2*PTS,minterpolate=fps=30:mi_mode=mci" -an out.mp4 |
Chaining two atempo filters is the safe way to go below 0.5×, since older FFmpeg builds limit a single atempo to between 0.5 and 2. minterpolate is slow and can warp edges and backgrounds; check the result.
How do you fix choppy slow motion?
You fix choppy slow motion by giving the editor more frames, either real ones (record at a higher fps) or made-up ones (interpolation):
| Method | How it works | Looks like |
|---|---|---|
| Frame sampling (default) | Repeats frames | Stutter |
| Frame blending | Mixes neighbouring frames | Smooth but ghosted |
| Optical flow / motion interpolation | Generates in-between frames | Smoothest; can warp fast or complex motion |
| Re-record at 60-240 fps | Real frames | Best |
Most editors (DaVinci Resolve, Premiere Pro, Final Cut Pro, CapCut) offer frame blending and optical flow in the clip's speed or retime settings. Interpolation struggles with hands, crossing objects and busy backgrounds, so for anything important, reshoot at a higher frame rate. Also check the shutter: slow motion recorded with a slow shutter has motion blur baked in, which looks soft when slowed.
What sounds good under slow motion?
Slowed speech rarely sounds good: even with pitch kept, words stretch unnaturally. For action shots, mute the original audio and add music or a sound effect. Remove the sound with the free video muter, or keep the original at normal speed for the real-time part of a clip and slow only the visual moment. Want a still from the exact frame of impact? The free frame extractor saves any frame as an image.
Going the other way? How to speed up a video or make it fast forward covers 2× to 8×.
Frequently asked questions
How do I slow down a video for free?
Use QuickVeed's free Video Speed Changer in your browser (0.75×, 0.5× or 0.25×), Google Photos on Android, or FFmpeg's setpts and atempo filters.
Why is my slow motion choppy?
The clip was recorded at too low a frame rate for the speed. 30 fps at 0.5× shows only 15 new frames a second; record at 60 fps or more.
What fps is best for slow motion?
60 fps for half speed, 120 fps for quarter speed and 240 fps for an eighth, played back at 24-30 fps.
Can I slow down a video without changing the pitch?
Yes. Keep the voice pitch option on in the speed changer, or use FFmpeg's atempo filter, which keeps pitch.
How long is a 10-second video at 0.5× speed?
20 seconds. At 0.25× it's 40 seconds.
Can I make normal video into smooth slow motion?
Partly, with optical flow or motion interpolation, but it can warp fast motion. Recording at a higher frame rate gives better results.
Try it with your own video
Add captions to your clips in 11 styles and 32 languages, then post them anywhere. Upload a clip, pick a caption style, and judge the result for yourself. QuickVeed plans start at $18/month, and new accounts get a 14-day trial with 250 credits, no card needed. Sign up or see pricing.
Sources
Competitor details in this post were checked against these public pages in October 2026. Products and prices change, so confirm with each vendor before you decide.
