Does the audio pitch change when I speed up a video?

No, not unnaturally. The atempo filter performs genuine time-stretching, adjusting tempo independently of pitch, so a voice sped up 1.5x sounds like someone talking faster rather than sounding artificially higher-pitched.

Why can't FFmpeg change speed beyond 2x in a single audio filter step?

The atempo filter is documented to only produce reliable results within a 0.5x–2.0x range per stage. For a 4x speed change, the tool chains two atempo=2.0 stages back to back (2 × 2 = 4), which is mathematically equivalent to a single 4x stretch but keeps each individual stage within its supported range.

What speeds can I choose?

Presets are available at 0.25x, 0.5x, 0.75x, 1x (original, disabled since there is nothing to change), 1.25x, 1.5x, 2x, 3x, and 4x.

Why would I slow a video down instead of speeding it up?

Slow motion is useful for analyzing sports technique, studying a dance routine frame by frame, or creating a dramatic effect in a highlight reel. Slowing audio-heavy content like a music lesson also gives more time to follow along with fast passages.

Does the video resolution or quality change?

No. Resolution, aspect ratio, and visual quality are unaffected by speed changes — the setpts filter only alters timing, and the video is re-encoded at a quality level equivalent to the original, not scaled down.

Can I change speed on a video that has no audio track?

Yes. If the source file has no audio, the tool simply applies the video-only setpts filter and produces a silent output at the new speed.

What input formats are supported?

MP4, MKV, AVI, MOV, and WebM are all accepted as input. Regardless of the source format, output is always a standard H.264/AAC MP4 for the broadest possible compatibility.

Will speeding up a long video make it finish processing faster?

No — processing time depends on decoding and re-encoding every frame of the source video, which takes roughly the same amount of computation whether the output plays back fast or slow. A 20-minute video takes about as long to process regardless of the target speed.

Can I create a slow-motion effect from normal 30fps footage, or do I need high frame rate source video?

You can slow down any footage, but the result will show the same number of frames stretched over more time, which can look choppier than true high-frame-rate slow motion filmed at 60fps or higher. For the smoothest slow-motion look, footage originally shot at a higher frame rate slows down more convincingly.

Is there a limit to how many times I can change a video's speed?

No usage limit on conversions — only a file size limit tied to your account tier, since processing happens entirely in your browser rather than on a server.

All ToolsChange Video Speed

Change Video Speed

Speed up or slow down any video — browser-based, no upload needed.

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Change Video Speed

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Drop your video file here

MP4, MKV, AVI, MOV, WebM — or click to browse

Select Speed

Your files never leave your device. All processing happens locally in your browser — nothing is uploaded to our servers.Files are never stored on our servers · No tracking of your file contentsPrivacy Policy

What is Change Video Speed?

Changing video playback speed sounds simple but involves two separate technical operations that have to stay coordinated. The video track is retimed using a presentation timestamp filter — every frame's scheduled display time is scaled by the inverse of the speed factor, so at 2x speed each frame is shown for half as long. Audio is a different problem entirely: you cannot just play samples back faster, because that would also raise the pitch, turning speech into the familiar "chipmunk" effect. Proper speed changes need a time-stretching algorithm that adjusts tempo independently of pitch.

This tool handles both halves correctly. The video stream is retimed using FFmpeg's setpts filter, and the audio stream is processed through the atempo filter, which performs genuine tempo-shifting rather than simple resampling — voices and music speed up or slow down without turning into a squeak or a drone. Because atempo's single-stage range is limited to between 0.5x and 2.0x, more extreme speed changes (3x or 4x) are achieved by chaining multiple atempo stages together, and the tool handles that chaining automatically so you can pick any speed from a quarter-speed crawl to four times normal without worrying about the underlying filter math.

How It Works

When you choose a speed multiplier, the tool builds a video filter of setpts=(1/speed)*PTS, which rescales every frame's presentation timestamp so the whole video plays back at the new rate. For audio, it builds an atempo filter chain: speeds within 0.5–2.0x use a single atempo stage, while faster speeds are split into successive atempo=2.0 stages (each doubling tempo) followed by a final fractional stage, since FFmpeg's atempo filter cannot exceed a 2x change in one pass. Both filters run together in a single FFmpeg pass, and the result is re-encoded as H.264 video with AAC audio into a new MP4 file — all inside your browser.

How to Use

1
Upload your video
Drop an MP4, MKV, AVI, MOV, or WebM file onto the upload area, or click to browse. The file loads directly into your browser.
2
Let FFmpeg load
On your first use, the ~30 MB FFmpeg WebAssembly engine downloads once and is cached for future conversions on this site.
3
Pick a speed preset
Choose from 0.25×, 0.5×, 0.75×, 1.25×, 1.5×, 2×, 3×, or 4×. The 1× (original) option is disabled since there is nothing to change.
4
Click Apply Speed Change
FFmpeg applies the setpts video filter and a matching atempo audio filter chain so picture and sound both shift to the new speed together.
5
Wait for processing
Because this re-encodes both video and audio, processing time scales with the source video's length and resolution rather than finishing instantly.
6
Download the result
Save the speed-adjusted MP4 to your device once the progress bar reaches 100%. Your original file is left untouched.

Who Uses This Tool

🎓

Compressing Long Lectures

Speed up a recorded 90-minute lecture to 1.5x or 2x so you can review it in a fraction of the time while the pitch-corrected audio stays intelligible.

🐌

Dramatic Slow Motion

Slow down a sports clip, a dance move, or an action sequence to 0.25x or 0.5x for a dramatic reveal in a highlights reel or creative edit.

🔬

Frame-by-Frame Analysis

Coaches and researchers slow down recorded motion — a golf swing, a lab experiment, a physical therapy exercise — to study details invisible at normal speed.

🎬

Fake Timelapse from Real-Time Footage

Speed up long, static recordings (a sunset, a construction project, a cooking process) 4x to compress hours of footage into a punchy, watchable clip.

♿

Accessible Instructional Content

Slow a fast-paced tutorial to 0.75x for viewers who need more processing time to follow spoken instructions or on-screen demonstrations.

🎵

Learning a Musical Passage

Slow down a recorded music performance to practice a technically difficult passage at a manageable tempo without the pitch dropping into an unrecognizable register.

Why Choose This Tool

True Time-Stretching, Not Pitch-Shifted Playback

The atempo filter changes tempo independently of pitch, so sped-up speech and music sound natural instead of turning into a squeaky "chipmunk" effect.

Handles Extreme Speeds Correctly

Speeds beyond atempo's 2x single-stage limit are automatically split into chained stages, so 3x and 4x speed changes still sound clean rather than distorted.

Nine Speed Presets

From 0.25x crawl to 4x fast-forward, with several intermediate steps in between for fine control over pacing.

100% Private Processing

FFmpeg WebAssembly re-encodes the entire video locally in your browser — nothing is uploaded to any server.

Broad Format Support

Accepts MP4, MKV, AVI, MOV, and WebM as input, and always outputs a universally compatible H.264/AAC MP4.

Free — No Watermark

No watermark added to output. Use free for standard file sizes — sign up free to raise your limit to 80 MB, or upgrade to Pro for 250 MB.

Also Try

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Key Benefits

Nine speed presets from 0.25x up to 4x
Audio uses real time-stretching, not simple pitch-shifted playback
Multi-stage atempo chaining handles extreme speeds correctly
Works with MP4, MKV, AVI, MOV, and WebM source files
Browser-based — your video is never uploaded
Output is a standard H.264/AAC MP4 for universal compatibility
No account needed for typical file sizes
100% free with no watermark

Frequently Asked Questions

Also Known As

change video speed online freespeed up video browser no uploadslow down video online free toolvideo speed changer ffmpeg browsermake video faster online freeslow motion video converter online2x speed video without losing audio syncvideo playback speed changer no software

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