RunToolRunVideo Cropper
Crop and resize your videos.
How to Trim a Video Online
Select a video
Click the upload area or drop an MP4, MOV or WebM file.
Set start and end times
Choose the exact segment you want to keep — the rest is cut away.
Download the trimmed clip
Save the selected part as a new MP4, processed entirely in your browser.
Cropping removes pixels permanently
Cropping discards the parts of each frame outside the selection and re-encodes what remains. The removed area cannot be recovered from the result, so the original is the only copy that still contains it.
Because the frames are re-encoded, cropping also costs a generation of quality. Cropping once from a high-quality source is fine; cropping a file that has already been compressed several times compounds the loss.
Cropping and resizing are different things
Cropping changes what is in the frame; resizing changes how many pixels represent it. Crop a 1080p video to its centre half and you have a smaller video at the same pixel density. Resize it and you have the same content with fewer pixels.
This matters for quality planning. A heavy crop of a 1080p source leaves a frame with fewer pixels than 1080p, so scaling it back up to fill a 1080p player produces a soft image. Cropping tightly is really an argument for shooting at a higher resolution than you need.
Aspect ratios and where they matter
Platforms want different shapes: vertical for phone-first feeds, square for some social posts, wide for traditional video. Cropping is how a single recording serves more than one, and doing it deliberately beats letting a platform crop automatically.
Automatic cropping centres the frame, which is frequently wrong. A subject standing to one side of a wide shot is exactly what a centre crop cuts in half.
Even dimensions and codec requirements
Most video codecs require frame dimensions divisible by two, and some encoders prefer multiples of four or sixteen. A crop to odd dimensions either fails or is silently adjusted by a pixel, which is harmless but explains why a requested size sometimes comes back slightly different.
This is also why a crop specified by dragging a box may not produce exactly the numbers you dragged. The adjustment is the encoder keeping the output valid.
What cropping cannot fix
It removes distractions at the edges of the frame, which is genuinely useful — a cluttered background, a stray hand, a watermark in a corner. It cannot change the composition of what remains, and cropping heavily to isolate a subject usually looks like exactly what it is.
For a subject that moves across the frame, a fixed crop either loses them or has to be loose enough to defeat the purpose. That needs tracking, which is editing rather than cropping.
How it runs here
The work is done by a WebAssembly build of FFmpeg in your browser, so personal recordings and internal screen captures stay on your machine. It is single-threaded, so a long or high-resolution video takes real time.
Trimming the clip to the part you need before cropping reduces the work proportionally, and it is usually the same edit you wanted anyway.