User Guide
Load the video
Drop in a file up to 300 MB. It appears in a player so you can find your in and out points by watching rather than guessing.
Set the start and end
Scrub to where the clip should begin and end. The tool works out the duration itself and passes it to the encoder, so you never have to calculate a length.
Choose Fast or Precise — this is the real decision
Fast copies the streams without re-encoding: instant, zero quality loss, but it can only cut on a keyframe. Precise re-encodes so the cut lands on the exact frame you chose.
Know what Fast will do to your start point
Keyframes typically sit 2–10 seconds apart. Fast mode snaps backwards to the nearest one, so your clip may begin a few seconds early. For a rough extract that is fine; for a cut on a specific word it is not.
Trim and download
Fast mode finishes in seconds regardless of length, because nothing is re-encoded. Precise mode runs at roughly real time for the trimmed section only — not the whole source.
Check the first second
With Fast mode, confirm the clip starts where you wanted. If it opened early, run it again in Precise mode. Both modes apply +faststart, so the result is ready for the web either way.
About the Video Trimmer
This tool cuts a section out of a video and gives you back just that section. It runs entirely in your browser, and it offers two genuinely different methods rather than one compromise — which is worth understanding, because picking the wrong one is the only way to get a disappointing result.
Why a video cannot be cut anywhere
Compressed video is not a sequence of independent pictures. To reach the file sizes we take for granted, H.264 stores occasional complete frames — keyframes, or I-frames — and then stores everything between them as a description of what changed. A P-frame or B-frame is meaningless without the keyframe it refers back to.
The stretch from one keyframe to the next is a group of pictures, or GOP. In typical recordings a GOP runs 2 to 10 seconds. Cut in the middle of one and the first frames of your clip have nothing to reference, which is the cause of the grey or smeared opening you may have seen from other trimming tools.
The two modes
| Fast | Precise | |
|---|---|---|
| Method | Stream copy — no re-encoding | Re-encode to H.264 |
| Cut accuracy | Nearest earlier keyframe | Exact frame |
| Quality | Identical to source | One generation of loss (CRF 23) |
| Speed | Seconds, any length | Roughly real time for the clip |
| Audio | Copied untouched | Re-encoded to AAC 128 kbps |
| Use it for | Rough extracts, long clips, archival | Cutting on a word or an action |
Fast mode is genuinely lossless. It does not decode a single frame — it copies the compressed data into a new container and adjusts the timestamps. That is why it takes the same few seconds whether you are cutting 10 seconds or 10 minutes, and why the result is bit-for-bit as good as the source. The cost is only that the start point snaps backwards.
Precise mode decodes and re-encodes the selected range at CRF 23 with the veryfast preset, which lets it place a fresh keyframe exactly where you asked. The FFmpeg seeking documentation explains the underlying mechanics of input versus output seeking that make this trade-off necessary.
Picking the right one
Use Fast when the exact opening frame does not matter: pulling a chapter out of a lecture, clipping a long recording down to a manageable size, keeping a segment for reference. You get perfect quality and it finishes immediately.
Use Precise when the cut point is the point: starting on a specific word, ending before someone walks into frame, matching a music beat, or producing a clip that will sit next to others in an edit.
A practical habit: try Fast first. It costs seconds. If the opening is wrong, run Precise. You will find Fast is adequate more often than not, and it leaves the quality untouched.
Why trimming beats compressing
If your goal is a smaller file, trimming is almost always the better first move. Size scales linearly with duration, and it does so at zero quality cost in Fast mode. Cutting a 10 minute recording to the 90 seconds that matter removes 85% of the file and loses nothing. Compressing the full 10 minutes to reach the same size would degrade every frame of it.
Trim first, and compress afterwards with the Video Compressor only if the trimmed clip is still too large.
Privacy and limits
Everything runs through a WebAssembly build of FFmpeg downloaded into the browser tab on first use (about 30 MB, cached afterwards). The video is never transmitted — there is no upload, no queue and nothing to delete afterwards. A single-threaded WebAssembly module can address only about 2 GB of memory, so files above 300 MB are rejected and anything over 60 MB warns that it will be slow.
Frequently Asked Questions
Why does my clip start a few seconds before the point I chose?
You used Fast mode, which cuts on keyframes. Compressed video only stores complete frames every 2–10 seconds, and Fast mode snaps back to the nearest one so the opening has something to reference. Use Precise mode for a frame-exact cut.
Which mode should I use?
Fast if the exact opening frame does not matter — it is instant and completely lossless. Precise if you need to start on a specific word or action. Try Fast first; it takes seconds, and if the opening is wrong you can rerun in Precise.
Does trimming reduce quality?
Not in Fast mode — it copies the compressed data without decoding it, so the result is identical to the source. Precise mode re-encodes at CRF 23, which costs one visually transparent generation.
Why is Fast mode so much quicker?
Because it never decodes anything. It copies the existing compressed frames into a new container and fixes the timestamps. That takes the same few seconds whether the clip is 10 seconds or 10 minutes long.
Can I cut multiple sections and join them?
Not in a single pass — the tool extracts one continuous range. Run it once per section and download each clip, then join them in a video editor if you need them combined.
Should I trim before compressing?
Yes, almost always. File size scales directly with duration, and Fast trimming costs no quality at all. Removing the parts you do not need is free; compressing the parts you do keep is not.
Where does the trimming actually happen?
No. The trim happens in your browser through a WebAssembly build of FFmpeg. Nothing is transmitted, which also means a long file is not limited by your upload speed.
What is a keyframe, in plain terms?
A complete picture. Everything between keyframes is stored only as the difference from what came before, which is how video files stay small. Cuts can only be made cleanly at a keyframe unless the video is re-encoded.