Changing playback speed in a player only helps you; the person you send the file to still gets the original pace. To share a sped-up cooking time-lapse, a slowed-down golf swing or a long tutorial at a brisker tempo, the speed has to be written into the video itself.
This tool does exactly that. Choose a speed between 0.25× and 4×, decide whether to keep the sound, and press Convert. The new file runs for a different length, for example a 60-second clip at 2× becomes 30 seconds, and voices keep their normal pitch instead of turning into chipmunks or growls.
How speeding up and slowing down a video works
Every frame in a video has a timestamp that says when it should appear. Changing the speed rewrites those timestamps: at 2× each frame appears after half the usual interval, at 0.5× after twice the interval. The frame rate of the file stays the same, so when a clip is sped up some frames are dropped, and when it is slowed down frames are repeated. No in-between frames are invented, which means a normal 30 fps clip slowed to 0.25× looks steppy. Footage shot in a phone's slow-motion or high frame rate mode has far more frames to work with and slows down much more smoothly.
Sound is handled separately. Simply playing audio faster raises its pitch, the classic chipmunk effect. Here the tempo is changed with ffmpeg's time-stretching filter, which keeps the pitch where it was; speeds beyond its 0.5× to 2× range are reached by chaining it, so 4× is two steps of 2×. Choosing Remove under Sound leaves the result silent, which is often the better choice for strong slow motion.
What people change video speed for
Time-lapses from ordinary footage
A long recording of a sunset, a drawing or a build becomes watchable at 3× or 4×. Combine with Remove under Sound when the original audio is only background noise.
Slow motion for sport and technique
Golf swings, dance moves and tennis serves are easier to analyse at 0.5× or 0.25×, especially if the clip was filmed at 60 fps or more.
Brisker tutorials and lectures
Saving a talk at 1.25× or 1.5× keeps speech intelligible and natural in pitch while cutting the running time by a fifth or a third.
Speeds, sound options and output
Speed offers 0.25×, 0.5×, 0.75×, 1.25×, 1.5×, 2× (the default), 3× and 4×. Sound offers Keep, same pitch, the default, and Remove. The output length is the original length divided by the speed, so 0.75× makes a 40-second clip about 53 seconds long. The file name gets the speed added, such as -2x or -0.5x.
Because every frame gets a new time, the video is always re-encoded, in its original container: MP4, MOV and MKV as H.264 with AAC sound, WebM as VP8 with Vorbis, AVI as MPEG-4 Part 2 with MP3. The work runs in your browser with the site's WebAssembly build of ffmpeg, downloaded once (about 31 MB) on first use. It uses one processor thread, so slowing down a long clip, which makes the output longer, takes noticeably more time than speeding it up. Several files can be queued and are processed with the same settings.
Cara memakai alat ini
- Drop one or more MP4, MOV, WebM, MKV or AVI files on the box above, or click it to browse.
- Choose a Speed from 0.25× to 4×.
- Under Sound, choose Keep, same pitch or Remove.
- Press Convert and download each result, or all of them with Download all (.zip).
Limitations
- One speed for the whole clip. Ramps, such as slowing down only the key moment, need a video editor; cut the moment out with Trim Video first and change its speed on its own.
- Slow motion repeats frames rather than creating new ones, so it is only smooth for footage shot at a high frame rate.
- At the extremes, 0.25× and 4×, time-stretched speech and music can sound smeared or slightly echoey.
- Subtitles inside the file are not kept, and external subtitle files no longer line up after a speed change.