How long does it take?

Longer than a desktop app. The encoder is ffmpeg compiled to WebAssembly and runs on one CPU core inside your browser tab, so it is several times slower than HandBrake or a native ffmpeg. In our test on a fast desktop, compressing 1080p video took about four and a half times the length of the clip, so a one-minute clip takes four to five minutes; laptops and phones are slower. The first run also downloads the roughly 32 MB encoder once.

Are my WEBM files uploaded to a server?

No. Your file is read into browser memory, processed on your own device, and released when you close the tab. Nothing is transmitted, stored, or logged at any stage.

Is there a file size limit?

Nothing is capped on our side, but the whole video and the result are held in browser memory. Clips up to a few hundred megabytes work on a desktop; larger files, or phones with little memory, can run out of memory and fail.

Which formats can I use?

MP4, MOV, M4V, WebM and MKV go in. The result is always an MP4 with H.264 video, which plays on practically every phone, browser and editor.

Updated for 2026 • 100% Free Online Video Tool

Free WEBM Video Resizer Online

This resizer scales your video to the height you choose, from 2160p down to 240p, keeping the aspect ratio. It re-encodes the picture as H.264 MP4 with ffmpeg running in your browser and copies the audio unchanged. Nothing is uploaded, but in-browser encoding is much slower than desktop software.

Your video is processed by ffmpeg running inside this tab, so nothing is uploaded. The first run downloads the ~32 MB encoder once. In-browser encoding is much slower than a desktop app such as HandBrake: expect a 1-minute 1080p clip to take several minutes to compress or resize.

Select or drop your WEBM video

MP4, MOV, WebM and MKV are accepted. The result is always an H.264 MP4.

100% Client-Side Private Processing

Your files are processed locally on your own device. Zero server uploads, zero file storage, and zero tracking.

Zero Server Logs

How WEBM Resizing Works

Pick a height (2160p, 1440p, 1080p, 720p, 480p, 360p or 240p); the width follows the original aspect ratio.
Both sides are rounded to even numbers, which H.264 requires, so a 1080p target from a 4:3 source gives 1440 × 1080.
The picture is re-encoded at CRF 23 (high quality). The audio track is copied without re-encoding.
Encoding runs on one CPU core inside your browser tab, so allow a few minutes per minute of HD video.

Step by step

How to RESIZE WEBM Files in 3 Steps

1
Select your video
Drop an WEBM, MOV or WebM file into the resizer.
2
Pick the output height
The dropdown shows the resulting width and height for your video.
3
Resize and save
Wait for the progress bar, then save the MP4.

Common Questions

Frequently Asked Questions

Everything you need to know about the free online WEBM resize tool.

Yes, but upscaling adds no detail; it only makes the file bigger. Resizing is most useful for shrinking 4K or 1080p footage for sharing.

Related Converters

Quickly jump between other popular image, document, and media formats.

PDF to JPG PPTX to JPG JPG to PPTX JPG to PDF JPG to TXT PNG to JPG JPG to PNG JPG to WEBP

Performance & SEO · 8 min read

AVIF vs WebP vs JPG: which format to convert to

How JPG, WebP and AVIF compress images, what the published size comparisons actually show, and how to serve all three so every browser gets the smallest file it can read.

Read the guide

Free WEBM Tools, No Sign-Up Required

Compress, resize, crop, and convert your files privately — every tool runs inside your browser.

Browse All Free Tools

No sign-up • No watermarks • Files never leave your device