v1.0
Suromeru — Free AI slow motion video maker
An AI draws the frames that were never there, between the ones your camera captured. That is what makes the motion fluid instead of stuttering the way stretched frames do. The audio can slow down with it. No upload, no install, everything happens in your browser.
Drop a video file
or click to choose · MP4 / MOV (H.264 · HEVC)
Nothing is uploaded · all processing happens in your browser · free, as many as you like
Updates
Fixed iPhone HDR (HLG) footage coming out with a brightness change every 4th frame.
Suromeru v1.0 released: a slow motion maker that draws the in-between frames with AI, entirely in your browser.
Found a bug? Please tell us via the contact form.
How to use
Choose a video
Drag and drop the clip you want to slow down (MP4 or MOV), or click to pick one. iPhone HEVC and HDR footage loads as is.
Pick how slow
2x, 4x or 8x. The higher the number, the slower the result, and the shorter the piece of source it can use (the result is at most 10 seconds).
Line up the moment
Use the slider to choose the instant you want slowed down. "Play this range" shows you exactly what will be used. Audio can be tape style, same pitch, or muted.
Make it and download
Press "Make slow motion" and the AI fills in the frames. You can watch the result right here before downloading it as MP4.
Frequently asked questions
Is it really free?
Yes, completely free, with no sign-up, and you can export as many clips as you like.
Is my video uploaded to a server?
No. Everything, including the AI, runs inside your browser. Your video never leaves your computer.
How is this different from normal slow motion?
Ordinary slow motion in an editor just holds each existing frame on screen for longer, which looks choppy. Frame blending fades between neighbouring frames, which makes moving objects look doubled. Suromeru estimates how everything moved between two frames and paints the in-between moment as a genuinely new image, so the result has more frames than the original and actually looks smooth.
Why only 10 seconds?
Every generated frame costs real computation on your machine. Allowing long clips would mean waits nobody would sit through. Capping the result at 10 seconds keeps most exports between a few dozen seconds and a few minutes, and the moment you want in slow motion is usually only a second or two anyway.
Why does 8x only allow 1.25 seconds of source?
Because the result is capped at 10 seconds: 10 ÷ 8 = 1.25. For the same reason 4x allows 2.5 seconds and 2x allows 5. You can place that window anywhere in the clip with the slider.
What happens to the sound?
You get three choices. "Tape style" drops the pitch along with the speed, exactly like slowing a tape down: one octave at 2x. "Same pitch" stretches the sound in time without lowering it, which keeps speech intelligible. "None" exports silence.
I get an error and it won't work
Suromeru needs WebGPU, a fairly new browser feature. Use desktop Chrome or Edge, or Safari 26 or later. Older browsers and some restricted environments will not work. The AI also needs a fair amount of memory, so closing other tabs can help.
Which formats are supported?
MP4 and MOV (ISOBMFF) containing H.264 or HEVC video. Phone recordings, screen captures and gameplay clips are almost always one of these. Exports are H.264 in MP4.
Can I use 4K footage?
You can load it, but the export is scaled down to at most Full HD (1920×1080), and the frame rate is capped at 30 fps. Working at 4K in a browser would make the wait impractical.
Fast movement comes out distorted
The AI infers the in-between from the two surrounding frames, so it struggles when motion is very large or when something is hidden behind a foreground object and then revealed. Lowering the speed (8x to 4x) or choosing a calmer moment usually fixes it.
Does it work on a phone?
It works in any browser with WebGPU: Safari 26 or later on iPhone, and a current Chrome on Android. The AI is slower on a phone than on a PC, so start with 2x and a short range.
It takes a long time
Processing time is almost entirely decided by your graphics hardware. A gaming graphics card finishes a 10 second export in under a minute; a laptop's integrated graphics can take several minutes. Lowering the speed, closing other tabs and apps, and plugging in the charger all help.
What to know about making slow motion for free, with no sign-up, in your browser
Stretched frames versus generated frames
Video is recorded at something like 30 frames per second. Slow it down four times by conventional means and each frame simply stays on screen four times as long, which reads as stuttering. Frame blending cross-fades neighbouring frames to hide it, but that just makes moving objects look transparent and doubled. Frame interpolation, which is what Suromeru does, estimates how far and in which direction everything moved between two frames and paints the intermediate moment as a new image. The result genuinely contains more frames than the original.
What works well, and what does not
Interpolation is happiest when motion is coherent and nothing appears or disappears: jumps, splashes, a pet turning its head, a golf swing. It struggles when a foreground object sweeps across and suddenly reveals background behind it, or when hundreds of leaves move independently in wind, because there is no single believable in-between for the AI to find. When a shot misbehaves, dropping from 8x to 4x or shifting the window by half a second often changes the result completely.
Two ways to slow audio down
One way is what happens when you slow a tape or a record: the pitch falls in proportion to the speed, exactly one octave at 2x and two octaves at 4x. It sounds dramatic and pairs naturally with slow motion. The other way chops the sound into short grains and re-lays them so the length changes but the pitch does not, which is what you want when speech has to stay intelligible. The larger the stretch, the more that second method takes on its characteristic smeared texture.
Everything stays on your machine
Suromeru downloads its AI model (about 10 MB) once, then talks directly to your computer's graphics hardware. Nothing is sent to a server, so family footage and client material are as safe as any local file. The trade-off is that speed depends entirely on your hardware: a gaming graphics card finishes in tens of seconds, while a laptop's integrated graphics may take several minutes.
How this differs from other slow motion services
Most slow motion services upload your video to a server, and come bundled with sign-ups, watermarked output and a push towards a paid plan. Suromeru differs in four ways: (1) nothing is ever sent, it all runs in the browser; (2) no account and no install; (3) no watermark and completely free; (4) instead of stretching frames, the AI draws new ones. The 10 second limit is what makes "finish it on your own machine" possible, and it is plenty for the decisive moment you want to slow down.