How this works in your browser
Unlike a trim or a mute, resizing cannot avoid a full re-encode: every frame has to be decoded, scaled to the new dimensions and encoded again, since the compressed data is tied to the original pixel grid. The tool scales each frame and re-encodes with H.264 and AAC using the encoder’s fastest preset, a necessary choice given that the WebAssembly build is single-threaded with no GPU access. Both dimensions are automatically rounded down to even numbers, because H.264 subsamples colour at half resolution and an odd dimension has no valid representation. Output is standardised to MP4 with the index written at the front so the file can begin playing before it finishes downloading.
Resize Video vs. traditional online converters
| Feature | Resize Video (in-browser) | Traditional online converters |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
Who uses Resize Video
Meeting platform dimensions
Convert footage to the exact resolution a social platform or ad network requires.
Shrinking 4K footage
Bring an oversized recording down to 1080p, which cuts file size far more than compression alone.
Faster sharing and streaming
Produce a smaller version of a clip that sends quickly and plays smoothly on mobile data.
Standardising a set of clips
Bring footage from different cameras to one resolution before assembling it.
How to use Resize Video
- 1
Open the Resize Video tool
Go to tools.slaytic.com and open the Resize Video tool. No sign-up or account required.
- 2
Drop your video file
Add any MP4, MOV, MKV, WEBM or AVI clip.
- 3
Enter width and height
Use even numbers that match your original aspect ratio to avoid stretching.
- 4
Download the resized MP4
Save the result, always encoded as H.264 video with AAC audio.
Frequently asked questions
Should width and height be even numbers?
Yes. The H.264 codec requires even dimensions, so use even numbers for both width and height.
Will this stretch my video if the aspect ratio changes?
Yes, if the new width and height don’t match the original aspect ratio, the video will stretch. Match the ratio to avoid distortion.
What output format do I get?
Always MP4 with H.264 video and AAC audio, regardless of the input format.
What dimensions should I use for common platforms?
Match the aspect ratio your destination expects and the numbers follow. Vertical video for phones is 1080 by 1920, square posts are 1080 by 1080, and standard widescreen is 1920 by 1080 or 1280 by 720. Picking a width and height from different ratios is what causes stretching.
Can I make a small video larger?
You can enter larger numbers, but it will not add detail. Upscaling stretches the pixels that already exist, so the result is a bigger, softer file. Resizing is worth doing downward and rarely worth doing upward.
Why must the numbers be even?
Because H.264 stores colour information at half resolution horizontally and vertically, so an odd dimension leaves it with half a pixel to account for. Odd values are rounded down to the nearest even number rather than rejected, so the encode always succeeds.
Is my video uploaded anywhere?
No. The resize and re-encode both run inside your browser tab.