Resize and rescale a video
Scale a video to 1080p, 720p, 480p or a custom size with an aspect-ratio lock and letterbox or crop fitting. Runs entirely in your browser.
- Runs in your browser
- Files are never uploaded
- Free, no account
First use downloads the 10 MB video engine from this site. After that it is cached and works offline. It is WebAssembly served from onthisdevice.com — no third-party CDN — and your file is still processed entirely on your own device.
How to resize a video
- Drop the video in. Its current resolution is read straight from the file.
- Pick a preset — 1080p, 720p, 480p and so on. Presets keep the original aspect ratio, so the width is derived for you.
- Choose Custom size… when you need an exact frame, then decide whether to letterbox, crop or stretch to reach it.
- Adjust quality under advanced options if the default CRF 23 is not right for you.
- Press Resize video and download the result.
Standard resolutions
| Name | 16:9 size | Pixels per frame | Relative encoding cost |
|---|---|---|---|
| 4K UHD (2160p) | 3840 × 2160 | 8.3 M | 4× of 1080p |
| QHD (1440p) | 2560 × 1440 | 3.7 M | 1.8× |
| Full HD (1080p) | 1920 × 1080 | 2.1 M | 1× (reference) |
| HD (720p) | 1280 × 720 | 0.9 M | 0.44× |
| SD (480p) | 854 × 480 | 0.4 M | 0.20× |
| Mobile (360p) | 640 × 360 | 0.23 M | 0.11× |
Letterbox, crop or stretch?
These only come into play when the target frame has a different shape from the source.
- Fit inside and pad (letterbox). The whole picture is kept and bars fill the gap. The filter chain is
scale=W:H:force_original_aspect_ratio=decreasefollowed bypad. Safest default, and the right choice for footage you did not shoot. - Fill and crop. The picture is scaled until it covers the frame, then the overflow is trimmed equally from both sides. Good for turning 16:9 into a 9:16 vertical clip when the subject is centred — and bad when it is not.
- Stretch. The picture is forced into the frame, distorting everything. Only useful for correcting footage that was squashed in the first place, such as anamorphic material with a broken aspect flag.
Common target sizes
| Where it is going | Aspect | Size to enter |
|---|---|---|
| Vertical short-form video | 9:16 | 1080 × 1920 |
| Square social post | 1:1 | 1080 × 1080 |
| Landscape social / web hero | 16:9 | 1280 × 720 |
| Email or docs embed | 16:9 | 854 × 480 |
Why widths and heights must be even
H.264 and VP9 store colour information at half the resolution of brightness — the 4:2:0 chroma layout — so each chroma sample covers a 2 × 2 block of pixels. An odd dimension leaves a half-block the encoder cannot represent, and it simply refuses the job. The tool rounds any value you type down to the nearest even number so this never becomes your problem.
Resizing always re-encodes
Changing the pixel grid means every frame has to be decoded, rescaled with a Lanczos filter and encoded again. There is no lossless shortcut, so pick CRF 18-21 if the result must stay visually identical to the source. If your goal is purely a smaller file rather than a specific resolution, compress video gives you a finer set of controls.
Questions
Should I letterbox or crop?
Letterboxing keeps the whole frame and adds bars, which is safest for footage you did not shoot. Cropping fills the frame edge to edge but cuts off the sides — useful for turning a landscape clip into a vertical one when the subject is centred.
Can I upscale a video?
You can, but you should not expect miracles: scaling up invents no detail, it only interpolates. The presets here are meant for scaling down, which genuinely reduces file size and decoding load.
Why are odd widths and heights adjusted?
H.264 and VP9 store colour at half resolution (4:2:0 chroma), so both dimensions must be even numbers. The tool rounds your input down to the nearest even value automatically.
Does resizing recompress the video?
Yes — changing the pixel grid requires a full decode and re-encode. Pick CRF 18-21 if you want the result to stay visually identical to the source at the new size.