Trimming without re-encoding: why it is fast and when cuts land a little off

What does re-encoding mean?

A video file stores compressed pictures. Re-encoding means decoding all of it and compressing it again. It is slow and loses a little quality each time. Copying the data without decoding it is called a stream copy.

Ready to try it? Open the trimmer and paste a link.

What is a keyframe?

Most frames in a compressed video only store what changed since the frame before. A keyframe stores a whole picture, and every frame after it depends on it. Keyframes appear every so often, not on every frame.

Why can a cut land a little early?

With a stream copy, a clip has to begin on a keyframe, because the frames after it can't be shown without one. If you ask for a start between two keyframes, the cut begins at the keyframe before it. The clip starts a little early and is otherwise unchanged.

When do I need an exact cut?

If the start must land on one exact frame, the video has to be re-encoded, which is slower and costs a little quality. A desktop video editor is the right tool for that. VideoTrimming cuts clips from direct files without re-encoding and keeps their original quality.

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