Cut a video without re-encoding
Enter the start and end of the section you want to keep. In fast mode, ffmpeg copies the video without re-encoding it: it's nearly instant and lossless, but the cut isn't frame-accurate.
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How to use it
- Install ffmpeg if you haven't already.
- Open a terminal in the folder containing your file.
- Copy the generated command, adjust the file names if needed, then run it.
- Open the resulting file to check the result.
Why the cut isn't exact
A compressed video contains keyframes, which are complete, and intermediate frames that depend on them. In copy mode, ffmpeg can only start at a keyframe: the clip generally starts at the one before the requested time, and so runs longer than expected. In our tests, a cut from 1 s to 4 s produced a 4 s clip instead of 3 s. Precise mode decodes and then re-encodes, which lets you cut to the exact frame but takes longer.
Why the start and end come before the file
In the command, the start and end options are placed before the source file: ffmpeg jumps straight to that position in the video without reading it from the beginning, which is much faster on long files.
Frequently asked questions
Why is my clip longer than requested?
In copy mode, ffmpeg can only start on a keyframe, usually the one before the requested start. "Precise" mode re-encodes the video and lets you cut exactly.
What format should I use for the time?
Hours:minutes:seconds (00:01:30), minutes:seconds (1:30) or seconds (90).