Make a video faster or slower in seconds — picture untouched, nothing uploaded.
Your files never leave your browser — all processing is local.
Drop a video
MP4, MOV, WebM or MKV — read in the browser, never uploaded
Only the timestamps change: the picture is not re-encoded, so slow motion repeats the same frames for longer and no in-between frames are made. Keeping the pitch can sound slightly warbly at 2× and above, or on music. The speed applies to the whole file. The file is not uploaded.
Drop an MP4, MOV, WebM or MKV file, pick a speed — 0.25× to 4×, with 2× preselected — choose what should happen to the sound, and export. The preview plays at the chosen speed right away, so you can judge the pace before anything is written. This is the page for a lecture or meeting recording you want to get through at 1.5×, a screen recording that should feel snappier at 2×, a pet or sports clip that deserves 0.5× slow motion, or a long recording turned into a 4× fast-forward. The file never leaves your computer.
A video file is a list of compressed frames, each stamped with the moment it should appear. Changing the speed only needs those stamps rewritten: at 2× every frame shows for half as long, at 0.5× for twice as long. So this tool copies the compressed video packets exactly as they are and writes new timestamps — no decoding, no new compression, no quality loss, and no waiting for an encoder to chew through every frame. The output keeps the same container as the input: MP4 stays MP4, MOV stays MOV, WebM stays WebM and MKV stays MKV. The flip side is that no new frames are invented either, which matters for slow motion — see the limits below.
Sound cannot be sped up by rewriting timestamps alone, so the audio track is always decoded and re-encoded; you choose how. "Keep pitch" (the default) stretches the audio in time without changing its pitch, so voices at 1.5× still sound like the same people, just talking faster. "Shift pitch" plays the sound faster or slower the way a tape machine would, so it gets higher when sped up and deeper in slow motion — the classic chipmunk or slowed-down effect. "Remove audio" drops the sound entirely and is the fastest, since nothing has to be encoded. Keeping pitch is a time-stretch algorithm, and at 2× or more, or on music, it can add a slight warble; that is a property of the method rather than a bug. Only the main audio track is processed: if the file carries extra tracks such as a commentary or a second language, they are left out and the page says so.
Because frames are only shown for longer, slow motion does not create in-between frames: a 30 fps clip slowed to 0.25× shows 7.5 frames per second and looks like a flipbook. 0.5× on a 60 fps clip is smooth; 0.25× on a 30 fps clip is not. In the other direction, speeding up raises the frame rate, and this tool caps the output at 120 fps so that players and hardware decoders are not handed a stream they refuse. A 60 fps video can therefore go up to 2×, a 30 fps video up to 4×; buttons beyond the limit are disabled and the page states the limit for your file. The whole clip gets one speed — to speed up just one part, cut it out first with Video Trimmer and join the pieces afterwards with Merge Videos. The preview uses the playback-rate feature built into your browser, which is not the same code as the export, so judge the pace from it but not the exact sound.
Audio is encoded as AAC for MP4 and MOV and as Opus for WebM and MKV. If your browser cannot encode either, the two sound options are disabled and only "Remove audio" remains — the page detects this when you open the file. When an MP4 or MOV has to fall back to Opus, some players, such as older versions of Windows Photos or some Safari versions, may play the picture without sound; Opus is the native codec of WebM and MKV, so the fallback only matters for MP4 and MOV. On desktop Chrome, Edge or Opera the output streams straight into a file you choose, so a long video never sits in memory; other browsers build it in memory with a limit of about 1 GB. Video Info shows what the file says about itself, including its frame rate, if you want to know the limit before you start.
No. The compressed video packets are copied exactly as they are; only the time at which each frame is shown is rewritten, so resolution, bitrate and codec are unchanged. The sound is the one part that is re-encoded, at a bitrate matched to the original track.
The range is 0.25× to 4×, but the ceiling depends on the frame rate. Speeding up raises the frame rate, and the output is capped at 120 fps, so a 60 fps video can go to 2× and a 30 fps video to 4×. Buttons beyond the limit are disabled and the page states the limit for your file.
Because no in-between frames are created. A 30 fps clip at 0.25× has only 7.5 frames per second, and every one of them is visible. Stay at 0.5×, or start from footage shot at 60 or 120 fps, and it looks much smoother. Inventing frames would mean re-encoding the picture, which this page does not do.
Not with the default. "Keep pitch" only changes the duration and leaves the pitch where it was. Pick "Shift pitch" if you want the higher or deeper voice on purpose. Keeping pitch can add a slight warble at 2× or more, or on music; that is how time-stretching works.
No — the whole file gets one speed. Cut the section out with Video Trimmer, change its speed here, then join it back to the rest with Merge Videos. None of the three re-encodes the picture, so nothing is lost along the way.
No. Your browser reads the file from your disk and writes the result back to your disk; there is no server in between. On desktop Chrome, Edge or Opera the output streams into a file you choose, so there is no length limit; other browsers build it in memory and stop at about 1 GB.
Because your browser can encode neither AAC nor Opus, or cannot decode the audio in this file. The picture only needs new timestamps, but the sound must be re-encoded, and without an encoder it cannot be kept. Open the page in a different browser, or export a silent version.