Trim Video

This trimmer copies the video and audio streams straight across into a new container instead of decoding and re-encoding them. Nothing is recompressed, so the trimmed clip is pixel-identical to the corresponding stretch of the original, and the operation runs at roughly the speed your device can read and write the file rather than the speed it can encode video. Cutting thirty seconds out of a two-gigabyte recording takes seconds, not minutes, and costs nothing in quality.

The output keeps the container the input used, so an MP4 stays an MP4 and an MKV stays an MKV. Start and end points are given as hours, minutes and seconds.

Why your cut may land slightly early

Compressed video is not a sequence of independent frames. Most frames describe only what changed since the frame before them, and they are only decodable in the context of a preceding keyframe, a complete self-contained image. Keyframes typically appear every two to ten seconds depending on how the file was encoded.

Because a copied stream cannot start mid-sequence, the cut has to begin at a keyframe. Ask for a start at 00:00:47 and the clip may actually begin a second or two earlier, at whichever keyframe precedes that moment. The alternative would be to decode and re-encode the opening section so it could start precisely where you asked, which would make the operation slower and lossy in exchange for frame-accuracy. For cutting the dead air off a screen recording or lifting a scene out of a long clip, landing on the nearest keyframe is almost always the better trade.

If you do need a frame-exact cut, trim generously here and make the precise edit in a video editor, where re-encoding is happening anyway.

Doing this in a browser tab

The work is done by FFmpeg compiled to WebAssembly, the same engine behind most desktop and server-side video tooling, running inside a worker on your own hardware. That is why there is no size cap to speak of and no upload wait, and also why a long file needs enough free memory on the device to hold what it is working on. A phone will manage a short clip comfortably and struggle with an hour of 4K, which is a hardware limit rather than a policy one.