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Pitch-preserving · WebCodecs hardware encode · No watermark

Change Video Speed

Speed up or slow down a video (0.25× to 4×) without pitch shift — pitch-preserving audio via atempo filter.

100% freeNo file size limitNo watermarkNo sign-up
  1. 1Pick file
  2. 2Configure
  3. 3Download
Pitch-preserving audio: voices stay natural at any speed (no chipmunk at 2×, no demon voice at 0.5×). On Chrome / Safari 17+ the re-encode uses your device's hardware H.264 encoder — typically real-time or faster.
  • Files never leave your browser — processed entirely on your device
  • No upload, no queue, no waiting for a worker to free up
  • No file-size cap from us — limit is your device's RAM

About Change Video Speed

AntiUpload's Change Video Speed tool re-times a video to any of five speed multipliers — 0.25× (4× slower), 0.5× (half speed), 1.5× (50% faster), 2× (double speed), or 4× (quad speed). The headline feature is pitch-preserving audio: speeding up or slowing down a video naively changes the audio's pitch (the chipmunk effect at fast speeds, the demon voice at slow speeds). We use FFmpeg's `atempo` filter, which uses Phase Vocoder time-stretching to preserve the original pitch regardless of playback speed. The result is a 2× lecture that still sounds like the original speaker, just talking faster — not Alvin & the Chipmunks.

Behind the scenes: the video stream gets its presentation timestamps rewritten via `setpts=PTS/<speed>` so frames pack closer in time (for fast playback) or spread out (for slow playback). The audio gets chained through `atempo` — the filter's range is [0.5, 2.0] per pass, so 4× and 0.25× chain two atempo filters in sequence (`atempo=2.0,atempo=2.0` for 4×, `atempo=0.5,atempo=0.5` for 0.25×). The `-shortest` flag truncates the output to whichever stream ends first; without it, setpts and atempo end at slightly different timestamps producing an audible silent-freeze tail at 2× and 4× speeds.

Hardware H.264 encoding via WebCodecs (when available — Chromium and Safari 17+) makes the re-encode fast. The shipped FFmpeg WASM is `--disable-asm` which is what makes libx264 5-20× slower than native; routing through the device's hardware encoder via WebCodecs sidesteps that entirely. On Firefox (which lacks WebCodecs H.264 encoder as of 2025), the tool falls back to software libx264 with `-preset ultrafast` and `-pix_fmt yuv420p` for compatibility — slower but produces identical output quality.

How it works

  1. Drop your videoAccepts MP4, MOV, WebM, MKV, AVI, M4V, FLV. Output is always MP4 (broadest compatibility after re-encode). No size limit from us.
  2. Pick a speed multiplier0.25× and 0.5× slow the video down (great for tutorials, language learning, deep video analysis). 1.5× and 2× speed it up (lectures, podcasts, content review). 4× compresses an hour of footage into 15 minutes of viewing.
  3. Click Change speedPitch-preserving audio rewires automatically — no manual atempo configuration needed. On WebCodecs browsers (Chrome / Safari 17+) the re-encode runs in seconds via hardware H.264. Firefox falls back to software encode.
  4. Download the time-shifted fileOutput is MP4 with the new playback speed baked in (it always plays at the new speed, regardless of player). Audio stays at the original pitch.

When to use Change Video Speed

Watching a 2-hour lecture / podcast at 2× without losing comprehension
Most video players have a 2× speed setting, but the speed-up is per-session — you can't share the sped-up version. Bake the 2× speed into the file and share that. The recipient sees the lecture at 2× without changing their player settings.
Slow-motion analysis of fast events
Sports replays, science experiments, dance technique review. 0.25× speed lets you see motion frame-by-frame at normal playback rates without scrubbing.
Tutorial pacing — slow the hard parts, speed the easy parts
Cut your tutorial into segments with our Video Trimmer, speed up the parts that show repetitive setup, slow down the parts that demonstrate the key technique. Combine with Video Joiner for a paced final.
Language learning at 0.5× speed
Slow native-speaker content to half speed without the pitch shift — pronunciation stays accurate while you have more time to parse each word. Used by language-immersion programs.
Time-lapse condensation of a long process
Multi-hour recordings of construction / cooking / nature can be 4×-sped to make them watchable. 4× compresses an hour into 15 minutes without the awkward time-lapse aesthetic of skipped frames.

Frequently asked questions

How to slow down a video without changing the audio pitch?
Use our Change Video Speed tool with the 0.5× or 0.25× setting. Audio pitch is preserved via FFmpeg's `atempo` filter (Phase Vocoder time-stretching). The voice sounds normal, just slower. Most other free video-speed tools change pitch along with speed — ours doesn't, by default.
Why does the audio sound slightly weird at 4× speed?
At 4× speed `atempo` is chained twice (atempo=2.0,atempo=2.0) because each pass is limited to a 2× ratio. The chained passes introduce mild artifacting on heavily processed audio (music, dense dialogue). For voice content the result is fine; for music the effect is more noticeable. 2× is the largest speed without chaining and has the cleanest audio.
Can I speed up a video to play normally but compressed?
That's not what speed-change does. Speed-change re-times the playback — a 1-hour 2× sped video is a 30-minute file that always plays at 2× the original timing. For "same playback timing but smaller file," use our Video Compressor or Video Converter.
Why is the conversion slower in Firefox than Chrome?
Chrome and Safari 17+ have hardware H.264 encoding via the WebCodecs API. We route through that automatically when available — 5-20× faster than software encoding. Firefox lacks a WebCodecs H.264 encoder, so we fall back to software libx264 in WebAssembly which is slower. The output quality is identical, just the time differs.
How to speed up an MP4 for free without watermark?
Drop the MP4 into our Change Video Speed tool, pick 1.5× / 2× / 4×, click Change speed. No watermark on the output. Compare to Kapwing (paywalls speed change above 1×), Veed ($25/mo to remove their watermark), and Clideo (watermarks free tier).
Does this work on long videos (1 hour, 2 hours)?
Yes, though the re-encode time scales with output length. A 2-hour video at 2× speed produces a 1-hour output — re-encoding 1 hour of HD video. On WebCodecs hardware that's ~2-5 minutes. On software libx264 it's 15-60 minutes. Close other tabs to free up CPU.
Can I pick a custom speed like 1.7× or 3.2×?
Not currently — only the preset multipliers (0.25 / 0.5 / 1.5 / 2 / 4) are exposed. These match the atempo filter's clean ratio points; custom speeds would need additional UI work to validate against the [0.5, 2.0] per-pass constraint. A custom-speed input is on the roadmap.

Related tools

Video TrimmerCut a clip out of a video — fast stream-copy by default, with optional frame-accurate re-encode and fade-in / fade-outCompress VideoShrink a video without obvious quality loss — CRF presets from "Best" to "Smallest", optional resolution downscaleAuto-Cut SilenceRemove dead air from podcasts and videos — silencedetect finds the quiet parts, the rest concats together. Adjustable threshold and paddingVideo JoinerCombine two or more videos into one — every input gets normalised to a common resolution and frame rate, then concatenated end-to-end