# Video Trimmer > Trim MP4, MOV, WebM or MKV in your browser — no upload, no re-encoding. Packets are copied as-is, so quality stays identical and a cut takes seconds. - URL: https://bytescope.dev/en/video-trim/ - Locale: en · Also: [ja](https://bytescope.dev/ja/video-trim.md) · [zh-Hant](https://bytescope.dev/zh-Hant/video-trim.md) - Runs: Your files never leave your browser — all processing is local. - Requires: Any modern browser can trim. Saving straight into a file you choose needs Chrome, Edge or Opera on desktop (File System Access API). Other browsers build the output in memory and stop around 1 GB. - Updated: 2026-09-08 ## What it does Drop an MP4, MOV, WebM or MKV file and it opens right away, even when it is several gigabytes: the trimmer reads it by random access instead of loading the whole file first, and nothing leaves your computer. You get a preview player and a timeline with every keyframe marked as a tick. Set the range by dragging the two handles, by pressing "Set in" / "Set out" at the current playback position, or by typing a timecode. The arrow keys step one frame at a time, and Shift + arrow jumps to the previous or next keyframe. ### Why the start moves a little earlier A compressed video only stores complete pictures at keyframes; every frame in between describes what changed since the frame before it. Because this tool copies packets instead of re-encoding them, a cut can only begin at a keyframe — starting anywhere else would leave the first frames with nothing to build on. So before you export, the trimmer tells you the actual start, for example "0.8 s earlier than you picked". If you would rather lose a moment than keep one, a single click snaps the start to the next keyframe instead. ### How this differs from video editing software An editor decodes every frame and encodes it again on export. That is what makes it slow, what costs a little quality every time, and what makes you choose export settings. Here nothing is decoded: the output is the same container and the same codec, and the frames are bit-for-bit the frames you started with, so the cut finishes at roughly the speed your disk can read the file. The trade-off is real, though. There is no frame-accurate cut, no multi-segment editing, no joining, and no cropping, resizing or compressing — all of those need re-encoding, and this page deliberately never does it. Rotation is not here either: if the video only plays sideways, Rotate Video fixes the orientation flag with the same copy, while actually turning the picture still needs re-encoding. The one extra you do get is a checkbox to drop the audio track. The result comes out in the same container it went in (MP4 to MP4, MOV to MOV, WebM to WebM, MKV to MKV). On desktop Chromium the trimmer streams straight into a file you choose, so a large video never has to sit in memory; other browsers build the output in memory, with a limit of about 1 GB. The output is a fresh container that carries only the video and audio packets — it does not copy the source's descriptive tags such as title, date or GPS location, which is worth knowing before you share a clip. When it is done, the same clip is one click away from MP4 to GIF, Extract Audio and Video Info. ## Limits Does not re-encode, cut to an exact frame, remove a middle section, join clips, rotate, crop, resize or compress. The start snaps to a keyframe. ## FAQ ### Does trimming reduce the video quality? No. The trimmer never decodes or re-encodes anything — it copies the compressed packets between your in and out points into a new file. The frames in the result are identical to the frames in the original, and the bitrate, resolution and codec are unchanged. ### How large a file can I trim? Reading has no practical limit, because the file is accessed piece by piece rather than loaded whole. Writing depends on the browser: desktop Chromium (Chrome, Edge) streams the output directly into a file you choose, so the whole video never has to be held in memory. Other browsers hold the result in memory and the tool stops at an estimated output of about 1 GB — shorten the range or switch to desktop Chromium for larger cuts. ### Can I trim iPhone videos? Yes. iPhone MOV files open like any other container, and copying packets does not care which codec is inside. If your computer cannot decode HEVC, the preview may stay black, but the cut still works and the result plays anywhere the original played. Files from cameras and phones vary a lot, so if a specific clip misbehaves, Video Info will show what is inside it. ### Why is the preview black? Your browser cannot decode that codec — HEVC/H.265 on a computer without an HEVC decoder is the usual case. Trimming does not need to decode anything, so you can still cut the file: the keyframe ticks on the timeline are read from the file structure and remain accurate, and you can set the range by timecode. The output will play wherever the original does. ### Why does my clip start earlier than the point I chose? Because a copied cut has to begin on a keyframe, and the closest keyframe before your chosen point may be up to a few seconds back, depending on how the video was encoded. The trimmer shows the actual start before you export. If you would rather start slightly late than slightly early, use the button that snaps to the next keyframe instead. ### Is my video uploaded? No. Everything happens in your browser: the file is read from your disk and the trimmed file is written back to your disk. There is no server involved, which is also why there is no waiting and no size cap on what you can open. ### Can I cut out the middle, join clips, or crop the picture? Not here. This page does one thing — a single range, copied without re-encoding. Removing a middle section, joining several clips, cropping, changing resolution or compressing all require re-encoding, which would make the tool slower and change quality. A video that plays sideways is the one exception: Rotate Video rewrites the orientation flag with the same copy, no re-encoding; actually turning the picture still needs an editor. For an animated snippet, hand the trimmed clip to MP4 to GIF; for anything heavier, a desktop editor is the right tool.