When trimming is the right fix
Most raw clips have dead weight at both ends: the second of fumbling before you hit record properly, the walk back to the phone after the moment is over. Cutting that off is usually the single biggest improvement you can make to a video before sharing it, and it also shrinks the file in direct proportion to the time removed. A 90-second phone clip at a typical 16 Mbit/s weighs around 180 MB; keeping only the 20 seconds that matter brings it down to roughly 40 MB before any other processing.
Typical jobs this tool handles well:
- Cutting a highlight out of a long recording, such as one goal from a full match or one answer from a recorded call.
- Removing a false start or a long silent intro from a screen recording.
- Getting a clip under a length limit, for example a 60-second short or a status update that only accepts 30 seconds.
- Preparing a short section before turning it into a GIF or extracting its audio.
What happens to your file
The video is opened by a local preview player, which is what gives you the duration and lets you scrub to find the exact frames you want. When you press Trim, the file is copied into FFmpeg running as WebAssembly in your tab, and FFmpeg decodes the section between your start and end points and encodes it again as H.264 video with AAC audio in an MP4 container.
Re-encoding is a deliberate choice. Simply copying the original stream without decoding is faster, but it can only cut at keyframes, which on phone footage may be one to two seconds apart. That is why some trimmers produce clips that start a moment early or open with a frozen frame. Because this tool re-encodes, the cut lands where you put the slider, to within a tenth of a second.
The encoder runs with a fast preset and a constant quality setting of CRF 23, which is the standard H.264 default and visually close to the source for most footage. The trade-off is that the fast preset is not the most space-efficient, so a trimmed clip can occasionally come out slightly larger per second than a heavily compressed original.
Setting precise start and end points
The two sliders move in 0.1-second steps, while the labels next to them show minutes and seconds. For frame-level precision, use the preview player as your guide:
- Play the video and pause just before the moment you want to keep.
- Drag the Start slider until its label matches the player position, then nudge it with the arrow keys after clicking on it.
- Repeat for End, and check the Duration line under the sliders before trimming.
If you move Start past End, the End point follows it, and the Trim button stays disabled until the clip has a positive length. Leave a few tenths of a second of padding on both sides; clips that start on the exact first frame of an action tend to feel abrupt when played back.
Speed, memory and long files
Everything happens on your own processor, so speed depends on your device rather than an internet connection. A few practical points:
- FFmpeg reads from the start of the file to find your section, so trimming the last minute of a long recording takes longer than trimming the first minute.
- The whole file is loaded into the tab's memory. On a laptop, files of several hundred megabytes are fine; on phones, keep it under a few hundred MB to avoid the tab being reloaded.
- The output resolution and frame rate match the source. 4K footage encodes several times slower than 1080p.
If you need to cut several pieces from one long recording, trim each piece in turn using the same file; the FFmpeg engine stays loaded between runs, so only the first one pays the start-up cost.
Troubleshooting
- The sliders never appear. The preview player could not read the file's duration, which usually means your browser cannot play that codec. HEVC footage from iPhones in some desktop browsers is the common case. Convert it with MOV to MP4 first, then trim the result.
- "Could not trim this file". The source is damaged or uses an unusual codec, or the browser ran out of memory. Try a desktop browser or a shorter source file.
- The trimmed file is still too large to send. Run it through compress video afterwards; a short clip compresses quickly.
The output is always named after your original file with a -trimmed.mp4 suffix, so it will not overwrite the source in your downloads folder.