How to Change Video Speed in Your Browser
Add Your Video
Drag a video onto the drop zone or click Select Video to pick a file. The tool shows the name, size and duration once metadata loads. Browser-side processing is used when supported by the file, browser, and device.
Pick a Speed
Tap a preset button such as 0.5x, 1.5x, 2x or 4x, or type any positive value into the custom speed box for fine control. Leave Keep Audio checked to retain sound; uncheck it to mute the output, which is the cleanest option for extreme speeds.
Process and Download
Click Change Speed and wait while ffmpeg.wasm loads and re-encodes the video. When it finishes you can preview the result inline, then click Download Video to save it. The file keeps its original container and is named with the speed suffix, for example clip-2x.mp4.
How Speed Settings Affect Video and Audio
The tool changes timing with the FFmpeg setpts video filter and, when audio is kept, the atempo audio filter. The atempo filter only adjusts tempo cleanly within a 0.5x to 2x range, so behavior outside that window depends on whether you keep or mute the audio. Use this table to choose the right setting.
| Speed Setting | Video Effect | Audio With Keep Audio On | Best Use |
|---|---|---|---|
| 0.25x | Very slow motion | Outside atempo range, so leave audio off for a clean result | Detailed slow-motion review |
| 0.5x | Half speed | Tempo matched, pitch stays natural | Tutorials and language practice |
| 1x | Unchanged | Untouched | Re-encode without timing change |
| 1.5x | Faster playback | Tempo matched, voices stay natural | Lectures and long recordings |
| 2x | Double speed | Tempo matched at the upper atempo limit | Skimming long footage |
| 4x and 8x | Time-lapse style | Outside atempo range, so muting is recommended | Time-lapse and quick scrubbing |
Choosing the Right Settings
Keep Natural Sound
If you need intelligible speech or music, stay within 0.5x to 2x and leave Keep Audio checked. In this range the atempo filter matches the audio tempo to the new speed without the chipmunk or deep-voice effect.
Go Faster Than 2x
For 4x, 8x or higher, uncheck Keep Audio. Outside the 0.5x to 2x window the audio tempo is not corrected, so muting gives the cleanest silent time-lapse output.
Hit an Exact Speed
When a preset is not precise enough, type the value directly into the custom speed box. Any positive number works, so you can enter 1.25x, 1.8x or 3x to fine-tune the result.
Pick the Right Device
ffmpeg.wasm needs a modern browser with SharedArrayBuffer, so use desktop Chrome or Firefox for the most reliable processing. Keep source files modest in size since the whole job runs in browser memory.
Common Problems and Fixes
Audio sounds wrong at high or low speeds
The atempo filter only corrects audio between 0.5x and 2x. At speeds outside that range the audio is left unadjusted, so it can drift in pitch or sync. For 4x, 8x or 0.25x, uncheck Keep Audio to mute the output instead.
Processing failed or will not load
ffmpeg.wasm requires a browser that supports WebAssembly and SharedArrayBuffer. If you see a load or processing error, reload the page and try again in desktop Chrome or Firefox, and confirm your internet connection since the core files load on first use.
The page runs out of memory on large files
The entire video is read into browser memory and re-encoded, so very large files can exhaust available memory. Trim or compress the clip first, or work with shorter segments, then change the speed of each part.
Processing is slow
Because FFmpeg runs locally in WebAssembly rather than on a server, encoding time scales with video length, resolution and your hardware. Close other heavy tabs, use a desktop machine, and expect a short re-encode for longer or high-resolution clips.