Free tools

Change video speed

Slow the pour, speed up the prep. The two speed changes that make a process video watchable.

Drop your video here, or click to choose
Slow motion or sped up · voices keep their pitch · nothing is uploaded

Everything happens inside your browser, using your own computer’s memory. Your file is never uploaded, never stored, and nothing is sent to us — so there is no limit on how often you use this.

How changing speed works

At a glance

Opens
Any video your browser can read — MP4, MOV, WebM, MKV
Saves
MP4 — H.264 video, AAC audio
Speeds
0.5×, 0.75×, 1.25×, 1.5× and 2×
Voices
Keep their natural pitch at every speed
Silent clips
Work too — only the picture is changed
Quality
Re-encoded once at CRF 23

How it works

Every frame in a video carries a timestamp saying when to show it. Changing speed rewrites those timestamps: at 2× each frame is shown after half the time, so a ten-second clip lasts five. The frames themselves are the same.

Sound is harder. Playing it faster the simple way squeezes the sound waves, which raises the pitch — the cartoon-voice effect. Here the sound is shortened in small overlapping slices instead, so it finishes sooner but every wave keeps its size, and a voice sounds like the same person talking quickly.

Faster picture, same voiceChanging speed rewrites each frame's timestamp, so at 2× a 10 second clip lasts 5 seconds. The sound is shortened with atempo, which keeps the waves the same size so the voice keeps its pitch. Simply playing sound faster squeezes the waves and raises the pitch.Picture: timestamps rewritten10 s5 s at 2×Sound: shortened, pitch keptoriginalatempo 2×same wave = same pitchjust fastersqueezed = higher pitchSlow motion from a 30 fps clip repeats frames;for smooth slow motion, film at 60 or 120 fps.
The picture's timestamps are rewritten; the sound is shortened without changing pitch.

Step by step

  1. Drop the videoIt opens in this tab. Nothing uploads. The first time, the browser downloads the 32 MB video engine and keeps it.
  2. Pick the speedThe line under the buttons shows how long the result will be.
  3. Change speedEvery frame is rebuilt. Keep the tab open while it works.
  4. DownloadThe file name says the speed. It stays in this browser until you press Delete.

Which setting for which job

If you are…Choose
Prep, setup or a walk across the room1.5× — still reads as real
A long process you want to feel like a time-lapse2×
A talking clip that drags a little1.25× — voices still sound natural
The payoff: the pour, the cut, the reveal0.5× — best from a clip filmed at 60 or 120 fps
A clip filmed at normal speed that you want smooth in slow motionRefilm at 60 or 120 fps if you can — see below

Under the hood

The technical detail, for anyone who wants to know exactly what happens to their file. Each line first says it plainly.

setpts

Rewriting when each frame is shown.

The picture filter setpts=PTS/speed divides every presentation timestamp by the speed. At 2× the timestamps are halved; at 0.5× they are doubled.

atempo

Faster or slower sound, same pitch.

ffmpeg's atempo filter time-stretches audio by overlapping and adding short slices of the waveform where they line up best, so the duration changes but the frequencies — the pitch — do not. It covers 0.5× to 2× in one pass.

Frame rate

Why slow motion needs a fast camera.

The output keeps your clip's frame rate. Slowing a 30 fps clip to 0.5× leaves 15 new pictures a second, so frames are shown twice and motion steps. Filmed at 60 or 120 fps, there are enough real frames for smooth slow motion.

Clips with no sound

Handled, not an error.

The tool checks whether the clip has a sound track before it starts. If it has none, only the picture is changed — asking atempo to work on missing sound would otherwise stop the job.

libx264 at CRF 23

Rebuilt so every player can play it.

Changing timing means re-encoding: H.264 with the veryfast preset at constant-quality CRF 23, 8-bit 4:2:0 colour, sound as AAC at 128 kbps, index at the front.

If something goes wrong

What you seeWhyWhat to do
Slow motion looks jerkyThe clip was filmed at 30 fps, so slowing it repeats frames.Film the moment in the phone's Slo-mo mode or at 60/120 fps, then slow it here.
The voice sounds a little smeared at 2×Time-stretching keeps pitch by overlapping slices of sound; at the extremes that can blur quick consonants.Use 1.5× for speech, and keep 2× for moments without talking.
It takes a long timeEvery frame is re-encoded on one CPU thread.Trim to the part you want to speed up first — shorter clips finish sooner.

Privacy: your file stays on your computer

The clip is re-timed in your browser, on your computer. The original never leaves your device.

What your browser downloads
The page — and, the first time you use a video tool, the video engine: about 32 MB, then kept in your browser's cache.
What it sends to us
Nothing. There is no upload step, no copy on our servers and no account. The work happens in your computer's memory.
How we know
Our automated tests run every tool while recording every network request the page makes. A single upload fails the test.
Where the result lives
In this browser only, until you press Delete. A finished file is still here if you close the tab and come back; a job still running stops when the tab closes.
Where your file goesRuzz's servers send the page and the video engine to your browser once. Your file is processed in your browser's memory on your own computer and is never sent back to the server.ruzz.app serverssend the page, keep nothingpage + engineonce · 32 MByour filenever sentYour browser tabffmpeg in WebAssembly · your CPU · your memoryYour fileread from diskprocessFinished filesaved by youKept in this browser until you press DeleteNo account · no quota · no watermark
Only the page and the engine come down. Your file never goes up.

Questions

Will the sound speed up too?

Yes, at the same rate, and without the chipmunk effect: the pitch stays natural.

What if my video has no sound?

That is fine — only the picture is changed.

Why is my slow motion choppy?

A normal 30 fps clip does not have enough frames for smooth slow motion. Film at 60 or 120 fps, or in the phone's Slo-mo mode, and slow that.

Can I speed up only part of a clip?

Not in one step. Trim out the part, change its speed, then put the pieces back together with Join clips.

Is my video uploaded?

No. The change happens in your browser, using your computer's memory.

A tool makes a file fit. It does not make people watch to the end — that is the hook, the order of the shots, the captions and the music. See how Ruzz does it.

Other free tools

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Crop to 9:16

Turn a landscape or square video into a vertical short for Reels, TikTok and Shorts.

Trim video

Cut the dead air off the start and end, or keep just the 30 seconds that matter.

Extract audio

Pull the sound out of a video as MP3, WAV or AAC.

Grab a cover frame

Pick any moment and save it as a vertical cover image.

Join clips

Filmed it in three takes? Put them end to end in one video — different shapes and silent clips are fine.

Video to GIF

Turn a moment into a GIF with real colours, not the grainy web palette.

Compress image

Shrink and resize a photo to JPG, WebP or PNG. Instant.

Remove sound

Take the audio off a video in seconds, picture untouched — then add a trending sound in the app.

Resize video

Exactly 1080×1920, 1080×1350, 1080×1080 or 1920×1080 — the size each platform asks for.