Trim MP4 and MOV videos and join several clips in order into one MP4. Choose fast trimming without re-encoding or frame-accurate trimming that also joins different videos. Nothing is uploaded.
Your files are processed only in this browser. Nothing is uploaded or stored.mp4box.js (BSD-3-Clause) · mp4-muxer (MIT) · WebCodecs
Video tools vary a lot between devices and browsers.Good to know. Due to technical limits, a computer can handle about 1 GB in total (about 10–20 minutes of Full HD) and a phone about 300 MB (a few minutes). Output is MP4 only.
Mode ① (fast cut) can’t handle fragmented MP4s (like screen recordings) or non-MP4 files — use mode ② (accurate cut) for those. In mode ②, videos your browser can’t decode directly are captured while playing, so it takes about as long as the video itself.
Safari 16.4+ mostly works, but re-compressing audio may fail in some versions. Firefox may not be able to save in accurate mode — Chrome or Edge is recommended.
Reading video info…
This browser can’t play a preview of this video. You can still trim it by typing times.
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Trim
Length
Drag the handles or type times (e.g. 1:05.5 or 65.5). With a handle focused, ←→ moves 0.1 s, Shift+←→ 1 s, and comma / period one frame.
Drop video files or choose them with “Add videos”. With several files, they are joined in list order.
Select a clip and set the part to keep with the start and end handles, the one-frame buttons or by typing times. Reorder clips by dragging or with the ↑↓ buttons.
Choose a save mode: ① Fast trim copies without re-encoding but snaps to keyframes (may differ by 1–2 seconds); ② Accurate trim cuts at the exact frame and can join videos of different sizes.
Click “Save as MP4”, watch the progress, then preview and download the result.
No. Reading, trimming and joining all happen inside this browser. Your files are never sent or stored anywhere, and the result disappears when you close the tab, so be sure to download it.
What’s the difference between fast and accurate mode?
① Fast trim copies the original data without re-encoding, so it finishes in seconds with no quality loss. But video can only start playing from a keyframe, so cut points snap to the nearest keyframe and may differ by 1–2 seconds, and only clips with the same codec, resolution and frame rate can be joined. ② Accurate trim decodes and re-encodes to H.264 + AAC, cutting at the exact frame you choose, and joins videos of different sizes by fitting them to the first clip. It takes longer.
Why MP4 only? Why not WebM?
MP4 (H.264 + AAC) opens almost everywhere — phones, messengers, social apps and video editors — so we only save MP4. WebM sometimes won’t open on some phones or editors. Browsers that can only produce WebM (such as Firefox in accurate mode) aren’t supported for saving; Chrome or Edge is recommended.
How large a video can it handle?
Because the whole video is processed in browser memory, a computer can handle about 1 GB in total (about 10–20 minutes of Full HD) and a phone about 300 MB (a few minutes). Larger files are blocked. Split longer videos into parts.
Why not use ffmpeg.wasm?
ffmpeg.wasm comes with complex LGPL/GPL license obligations, needs a download of over 30 MB before it can start, and requires special server security headers (COOP/COEP) to run fast. Instead this tool uses the browser’s built-in WebCodecs plus the lightweight mp4box.js and mp4-muxer, so it opens instantly and stays light.