You change a video's speed by adding the clip to a browser-based retimer, dragging the slider between 0.25x and 4x or tapping a preset, choosing how the audio is handled, and exporting an MP4. The encoding runs on your own machine with FFmpeg, so the video is never uploaded anywhere.
Speeds below 0.5x and above 2x are built by chaining audio tempo steps, so voices keep their normal pitch instead of turning into a chipmunk effect. The two limits worth knowing up front are the range itself, which stops at 0.25x and 4x, and the fact that slowing a clip repeats existing frames rather than inventing new ones. A 30 second clip at 2x becomes 15 seconds, and the tool shows that new length before you export. Nothing is installed, no account is created, and there is no daily cap on how many clips you retime.
Changing a video's speed sounds like a one minute job until you try it. Desktop editors bury it in a timeline menu, phone apps often watermark the export, and web converters want the file uploaded to their servers before they will touch it. A browser-based retimer skips all three: open a page, pick a multiplier, download the result.
Video Speed Changer
Retime any clip from 0.25x to 4x, keep the audio pitch or mute it, and export an MP4. The video stays on your device.
Slow motion and speed up, in the browser
The Video Speed Changer accepts MP4, WebM, MKV, MOV and AVI files and rewrites their timing. The slider runs from 0.25x to 4x in steps of 0.25, with presets at 0.5x, 1x, 1.5x, 2x and 4x for the common cases. Video is retimed with FFmpeg's setpts filter, which rewrites the presentation timestamp of every frame, and the audio is handled separately depending on the mode you pick.
The tool reports the estimated output length as you move the slider, so 2x on a 30 second clip shows 15 seconds before you commit to anything. At 1x the export button stays disabled, because nothing would change and a pointless re-encode would only cost time and a little quality. The export always produces H.264 video with AAC audio in an MP4 container, written so it can start playing before the whole file has arrived.
All of the work happens inside the browser tab. FFmpeg is compiled to WebAssembly and runs on your machine, so the clip is read from your disk, encoded locally and handed back as a download. There is no upload step, no account and no cap on how many files you process. The first run does fetch the engine, roughly 30 MB of code, and it is cached afterwards so the tool keeps working offline.
| Aihangsoft Video Speed Changer | Upload-based speed converter | |
|---|---|---|
| Where the video goes | Stays in the browser tab | Sent to their servers |
| Account | Not needed | Often required past a small file size |
| Watermark | None | Common on free tiers |
| Runs offline | Yes, after the first load | No |
| Speed control | 0.25x to 4x in steps of 0.25 | Usually a handful of presets |
How to change the speed of a video
The whole flow is four steps, and only the last one takes measurable time.
- Add your video. Drop the clip onto the page or click to browse. It is read from your disk into the tab, and the engine loads on first use. Clips under 500 MB and a few minutes long are the comfortable range.
- Pick the new speed. Drag the slider to any value between 0.25x and 4x, or tap one of the presets. The estimated output length updates immediately so you can see how much shorter or longer the result will be.
- Choose how the audio is handled. Keep pitch is the default and stretches the soundtrack so it matches the new video length without changing the pitch. Mute audio drops the soundtrack and gives you a silent clip.
- Export and download. Press Change speed, wait for the progress bar, then download the MP4. The result panel shows the new duration and the file size before you save it.
Expect the export to take longer than the editing itself. Changing speed means the video is re-encoded frame by frame, so processing time depends on the clip length, its resolution and your CPU, not on a server somewhere. Short clips finish in seconds and longer 1080p files can take minutes.
Video Trimmer
Need only one section at a different speed? Cut the clip first, then retime the piece you kept.
What Keep pitch actually does
Speed and pitch are tied together in normal playback, which is why a tape played too fast sounds like a chipmunk. Keep pitch breaks that link. The tool runs FFmpeg's atempo filter over the soundtrack, and atempo is a time stretch: it changes how long the sound lasts without changing its frequency. A voice at 2x is still recognisably that voice, and a song keeps its key.
There is a catch in how atempo works. A single atempo step only accepts a factor between 0.5 and 2.0, so anything outside that window has to be split into several steps and applied in series. The tool does that automatically: 4x becomes atempo=2.0,atempo=2.0, 0.25x becomes atempo=0.5,atempo=0.5, and a moderate 1.5x needs just the one step. The result is the same pitch-shifted-free sound at every setting on the slider.
| Audio option | What it does | When to pick it |
|---|---|---|
| Keep pitch (default) | Time stretches the soundtrack with atempo so it matches the new length without changing pitch | Talking head clips, interviews, music, anything with speech |
| Mute audio | Removes the audio track entirely and exports a silent video | Clips you will add music to later, or footage where the sound is unusable |
Keeping the pitch is not the same as keeping the quality. Time stretching works by repeating and shortening tiny slices of sound, and the more you stretch, the more that process is audible, so music at 4x can sound slightly smeared or metallic even though the notes are correct. It also cannot recover detail that was never in the source: stretching a thin, low bitrate track leaves a stretched thin track.
What 0.25x to 4x cannot do
These are the cases where the tool is the wrong answer, and they are worth knowing before you start rather than after.
- The range stops at 0.25x and 4x. There is no 10x, 50x or 100x. Extreme time lapse, where hours of footage compress into seconds, needs an editor that can drop the frame rate far below the source, not a speed slider.
- Slow motion repeats frames, it does not invent them. The retiming changes timestamps with setpts, so it has no way to create pictures that were never captured. A 0.25x clip simply holds each existing frame for longer, which reads as steppier and less fluid than footage genuinely shot at a high frame rate. If you want smooth slow motion, the capture frame rate matters more than any setting here.
- Speeding up discards frames. At 4x the clip covers four seconds of source footage in every second of playback, so the motion is sampled far less often and looks choppier than the original. The further past 2x you go, the more visible it becomes.
- Every export is a re-encode. There is no fast lossless mode, because the timing of the frames genuinely changes. That means an output quality and time cost on every run, even though the settings are chosen conservatively.
- One speed for the whole clip. You cannot mark a section and slow only that. Mixed-speed results need the clip cut into pieces first, then retimed separately and joined back together.
- Long or heavy files are hard on the machine. The first run pulls about 30 MB of engine code, and browser memory puts a practical ceiling on how large a video you can process in a tab.
When to trim first
Because the speed applies to the entire clip, the natural workflow for a partly slowed video is to cut it into the parts you want, retime the relevant one, and put the pieces back together.
- Cut the section you need. Use the Video Trimmer to isolate the moment, so the retimer only ever sees the part that needs a different speed.
- Retime that piece. Set the speed here, keep or mute the audio, and export. A shorter clip also encodes much faster.
- Reassemble if needed. Put the untouched parts and the retimed part back in order with a merger. Nothing has left your device at any point in this chain.
There is a second reason to trim first even when you want the whole clip at one speed: the export time scales with the length of the video, so removing footage you were going to cut anyway is free time saved. The same logic applies to resolution, since a large 4K source costs more to encode than a 1080p one, and dropping it before retiming is cheaper than doing it afterwards.