Change video speed
Speed up or slow down a clip with setpts and atempo.
Runs in this tab. The file stays here.
This runs in your browser. Nothing is uploaded. Longer clips take longer here than they would on a fast server — that is the trade-off for not sending the file.
About Change video speed
Speeds up or slows down a clip in the browser with setpts and atempo. Nothing is uploaded.
Speed is a number. 2 is twice as fast. 0.5 is half. Audio uses chained atempo filters because FFmpeg will not accept a single atempo outside 0.5–2. Video timestamps are scaled with setpts. The result is re-encoded, not a stream copy, so a long source still takes a while.
Change video speed runs FFmpeg compiled to WebAssembly in this tab. The first visit of a video or audio tool fetches about 30 MB from this origin; after that it can stay cached. Your file is not in that download and is not POSTed anywhere. GPL FFmpeg, single-thread, same origin, no COEP experiment. That is the same encoder as convert, trim, and compress — this page is just a different argument list, with the same honesty about what the core cannot mux.
You can open the network panel and watch. Encoding a long clip on a phone is slow because it is your CPU. That wait is the trade for not handing the file to a converter you found in a search ad. Reverse and boomerang cap duration so a two-hour file does not try to live backwards in RAM. If a codec inside a familiar extension is missing from this core, you get an error rather than a silent broken file. Subtitle generation and stem splitting are not here; I will not pretend they are. Missing is better than a watermarked demo.
How to use Change video speed
- 1Drop a clip.
- 2Set speed.
- 3Click Change speed, then download.
What it won't do
- Re-encodes the whole file.
- Speed is uniform, not keyframed.
Common questions
Will 4× speed keep the pitch?
atempo keeps pitch. It is not a vinyl slowdown. Extreme values still sound like a chipmunk-free fast talker, just denser.
Does change-speed upload the file?
No.
Why not a timeline editor?
Because this is a speed tool, not Premiere. Trim first if you only want a section sped up.
Related tools
Why this one doesn't upload your file
There is no server to upload to. This page is a static file, and the work happens in your browser using the same graphics and WebAssembly code that renders every other site you visit. Your file is read from disk into memory, processed, and handed back as a download. Once the page has loaded you can disconnect from the network entirely and it keeps working. The longer explanation