What if I only set width or height?
CutFast automatically calculates the other side to keep aspect ratio.
Resize MP4 Video Online
Right in your browser. Resize MP4 locally and export a new file — no uploads.
FAQ
Does resizing require re-encoding?
Usually yes. Resizing changes resolution, so encoding a new file is typically required.
Does resizing reduce file size?
Usually. Lower resolution often reduces bitrate and file size (depends on codec and quality presets).
Which browsers are supported?
The fast path relies on WebCodecs — recommended: latest Chrome / Edge.
Which formats are supported?
Common inputs: MP4/WebM/MOV/MKV. Output containers: MP4/WebM/MOV/MKV.
Are my files uploaded?
No. Processing happens locally in your browser.