Trim Video

What this tool does

Drop a video, set a start and an end, and save just that section. The tool opens the file on your device and reads its frame table — the display time of every frame, taken from the index without decoding anything — so the two handles move by frames, not by guesswork: the ← → keys step one frame, Shift steps ten, and a time such as 1:23.5 can be typed straight into the box. The stage shows the frame under whichever handle you moved last, and Play runs through the selected section silently so you can check it.

There are two ways to cut, and the difference matters. Fast mode copies the compressed video as it is: no re-encoding, no quality change, and a 2 GB recording is done in seconds. The price is that the start can only land on a keyframe — the small ticks on the timeline — so the start handle snaps to the nearest one before it. Exact mode re-encodes the section and cuts on the precise frame you chose, at the cost of a minute or so per few minutes of video. The output keeps the input's container: MP4 stays MP4, MOV stays MOV, WebM stays WebM.

How to use it

Drag the left handle to where the clip should begin and the right one to where it should end. Whichever handle you touched last is the active one: the ‹ › buttons, the arrow keys and the timecode box all act on it, and the Start / End switch lets you pick the other without dragging. The line next to the switch shows the two times and the length of the selection. Press Play to preview the section; it plays without sound, since only the picture is decoded.

Then pick Fast or Exact and press Trim. In fast mode the note under the buttons tells you how far apart the keyframes are in this file — typically 1 to 5 seconds for phone footage, up to 10 seconds for screen recordings — which is the most the start can move back. If the file's codec cannot be decoded by your browser, the stage stays blank and exact mode is unavailable, but fast trimming still works, because copying does not need a decoder. The result appears with a thumbnail, its length and its size, ready to download or to hand to Video to Image, Remove Audio or Video to MP3.

Things worth knowing before you cut

Why the start snaps in fast mode: compressed video stores a full picture only at keyframes and describes every frame in between as a difference from its neighbours. A decoder can start playing only at a full picture, so a copy that began between keyframes would show garbage or black until the next one. Snapping the start backwards keeps every frame you asked for; the end has no such limit and lands within one frame of your choice. Some editors and phones write a keyframe every 10 seconds or more; if the snap is too coarse for you, exact mode is the answer. Exact mode re-encodes with your browser's hardware encoder — H.264 into MP4 and MOV, VP9 into WebM — and the audio is copied unchanged in both modes. Variable-frame-rate recordings (screen captures, some phone clips) show a frame count that reflects the real frames, not a nominal rate; the timeline handles that correctly.

Background: keyframes and stream copy

The keyframe idea is as old as digital video standards. MPEG-1, published as ISO/IEC 11172 in 1993, defined I-frames (intra-coded, complete pictures) and P- and B-frames that predict from other frames; the run from one I-frame to the next is a group of pictures, or GOP. H.264, ISO/IEC 14496-10 from 2003, kept the same structure and is still the codec in most MP4 files. Cutting a compressed stream without decoding it — what ffmpeg calls stream copy — has therefore always meant starting at an I-frame. Editing software hides this by re-encoding everything, which is why exporting a 30-second clip from a desktop editor can take longer than the clip itself. This tool exposes the choice instead of hiding it: keep the original bits and accept the keyframe grid, or re-encode and get the exact frame.

Where it is used

Cutting the first ten seconds of a phone recording before sending it; pulling one answer out of an hour-long meeting or lecture recording; making a short clip from a screen capture for a bug report or a tutorial; shortening a dashcam file to the seconds that matter; trimming a game recording to the highlight. After cutting, Video to Image grabs a still from the clip, Remove Audio strips the sound, and Video to MP3 keeps only the sound. For a clip that plays sideways, Rotate Video fixes the orientation without re-encoding either.

Frequently asked questions