Video Resizer
Change a video's pixel dimensions by preset, by width, or by an exact width and height you specify.
Convert with this tool
or choose a file from your device — it is processed in this tab and never uploaded
Accepted: MP4, MOV, MKV, AVI, WebM, M4V
Files stay on your device. There is no upload, no queue and no watermark, so a conversion works even with the network switched off after the page has loaded.
Supported formats & processing
| Accepted input | MP4, MOV, MKV, AVI, WebM, M4V |
|---|---|
| Produced output | MP4, WebM or MKV at the new dimensions |
| Processing | FFmpeg.wasm (video engine, downloaded on first use) |
| Upload required | No — the file is read locally and never transmitted |
How to use this tool
- Add the videoThe source resolution is read from the container where available.
- Choose a preset, or switch to custom sizingPresets cover the common delivery targets.
- Use By width to keep the aspect ratioThe height is calculated automatically and rounded to an even number.
- Use Exact only when a spec demands itNon-matching aspect ratios will stretch the picture.
- Convert and check the result cardThe filter that was applied is printed so you can verify the maths.
About this tool
Resizing a video means re-encoding it at different pixel dimensions. Three approaches cover almost every need: pick a standard preset such as 1280 × 720, set a width and let the height follow to preserve the aspect ratio, or give an exact width and height when a delivery specification demands it.
The tool builds the correct FFmpeg scale filter for your choice. When you let the height follow, it uses a divisibility-aware filter so the output dimensions stay even, which H.264 requires — an odd dimension would break encoding, and that is the single most common cause of a failed resize elsewhere.
Features
- Presets for 1080p, 720p, 480p, 360p and square output
- Aspect-ratio-preserving resize by width
- Exact width × height mode for delivery specifications
- Even-number enforcement so H.264 encoding never fails on odd dimensions
- The exact scale filter used is reported in the result card
- Output to MP4, WebM or MKV
Frequently asked questions
What happens if I use an exact size with the wrong ratio?
The picture is stretched or squashed. The result card shows the output dimensions, and the video aspect ratio calculator can tell you the correct matching height for any width.
Does downscaling improve quality?
It does not add detail, but a smaller frame needs fewer bits, so at the same bitrate the picture looks cleaner. That is why downscaling and compressing usually go together.
Can I upscale to 4K?
You can, but the extra pixels are interpolated rather than real. Upscaling is only worth doing for compatibility with a delivery specification, not to gain detail.
Why does the file get smaller when I only change the size?
There are fewer pixels to encode, so the encoder needs fewer bits per frame at the same quality target. It is one of the most effective ways to reduce a file.