Video Trimmer

Video Trimmer cuts the start and the end off an MP4, MOV or WebM video in your browser, with a fast keyframe cut or a frame-exact cut. It is for the phone clip with ten seconds of fumbling at the start, the screen recording that runs on after the demo, or the part of a long video you want to send on its own. The page tells you plainly which kind of cut you got and where it really starts.

How to use

1. Drop one video on the box, or click it to choose it. Its length and picture size appear, with a player.
2. Pick the Cut. Fast copies the video as it is, so it is quick and loses no quality, but it can only start on a key frame. Exact decodes and encodes the video again, so it starts on the frame you chose, but it takes longer.
3. Type the Start and the End, as seconds such as 12.5 or as minutes and seconds such as 1:05. Or play the video, pause where you want, and press Use the player’s time as start or as end.
4. Press Trim video, then Download the new file. WebM stays WebM; MP4 and MOV become MP4.

Examples

A test video of 8 seconds, 480 by 270 pixels, whose only key frame is its first frame, cut from 2.5 to 5. With Fast, the result is 5 seconds long, from 0:00 of the original, and the page says the fast cut starts at the key frame at 0:00, before the 0:02.5 you chose. With Exact, the result is 2.5 seconds long, from 0:02.5. Phone videos usually have a key frame every second or two, so a fast cut there lands much closer to the start you typed.

Limits

One video at a time, up to 500 MB, as Quick facts shows; the new file is built in memory, so a phone may run out of memory sooner. A cut must be at least 0.1 seconds long, a minimum we chose. The end of a fast cut can also run a fraction of a second past the end you typed, to the edge of the last piece of video it copies.

The exact cut needs your browser to decode and encode video with WebCodecs. The page asks the browser when the video opens; if it cannot, only the fast cut is offered and a note says why. The exact cut encodes the video again, so the picture can lose a little quality, and the sound is copied as it is. Files with more than one video or sound track keep only the main one.

FAQ

Is my video uploaded to cut it?

No. A background worker in your browser reads the video in pieces and writes the new file on your device. Nothing is sent to a server.

Why did the fast cut start earlier than I asked?

Most videos store a full picture only now and then, at key frames, and the frames between depend on it. Copying without re-encoding has to begin at one of those, so pick Exact if the first frame matters.

Can I cut a piece out of the middle and keep both ends?

Not in one step. Trim the first part and the last part as two files; this tool does not join videos.