How to use the Trim Video
- Add the clip, then type the start time, for example 0:42 or 42.
- Enter where the cut should stop, or leave that box empty to run to the end.
- Pick Exact or Fast, press Trim, and save the shortened file.
Exact or fast?
Video is stored as occasional keyframes with lighter frames in between that only describe changes. Fast mode copies the packets as they are, so it can only begin on the nearest keyframe at or ahead of your start point; the clip may open a second or so early, but nothing is re-encoded and long files finish quickly.
Exact mode re-encodes the kept part, so the opening frame matches your start time precisely. MP4, MOV, WebM and MKV are handled by WebCodecs at a high quality setting; other formats go through ffmpeg in WebAssembly, which re-encodes the audio too so sound and picture start together.
How to write times
Plain seconds (95), minutes:seconds (1:35) and hours:minutes:seconds (1:01:35) all work, and decimals give tenths (1:35.5). Typing a start beyond the clip’s length, or an end earlier than the start, gives a clear error instead of an empty file.
The result keeps the source format and gets “-cut” added to its name, so saving it never overwrites the original recording.
Speed
Exact mode only processes the part you keep, so pulling a 20-second excerpt from an hour of MP4 means encoding only that excerpt. Fast mode costs about as much as reading the file.
Exact cuts of long stretches from AVI, WMV or other formats that rely on WebAssembly take far longer than the same cut from an MP4.
Questions
Can I cut a piece out of the middle?
Not in one pass. Save the section ahead of it and the section after it as two separate trims.
My fast cut starts too early. Why?
It begins at the previous keyframe. Switch to Exact when the opening frame matters.
Is my recording uploaded?
No. Cutting happens in your browser tab.