You've just recorded your screen and the file is a .webm. Great format for browsers — but your video editor doesn't support it, your client wants an MP4, or you need a GIF for a Slack message. Most online converters solve this by uploading your file to their servers, processing it, and returning it — which means your private screen recording just sat on someone else's computer.
The WebDesks Media Converter is different. It converts WebM to MP4 (or GIF, or WebM VP9) entirely in your browser using FFmpeg compiled to WebAssembly. Your files are never uploaded. No server receives them. No one else ever sees them.
Convert now: Open the WebDesks Media Converter — drop your WebM, choose MP4, download. Done.
What the Media Converter Can Do
The WebDesks Media Converter has two modes: video conversion and image resizing. Switch between them using the tabs at the top of the panel.
Video: WebM → MP4 / GIF / WebM
- WebM to MP4 (H.264) — the most universally compatible output. Works in QuickTime, Windows Media Player, iPhone, Android, and all major video editors.
- WebM to WebM (VP9) — re-encode for better compression while keeping the WebM format.
- WebM to Animated GIF — convert screen recordings to GIFs for sharing in documentation, Slack, Notion, or GitHub issues.
Image: Resize & Compress
- Resize images — specify target dimensions in pixels or percentage. Maintains aspect ratio by default.
- Compress images — reduce file size while controlling output quality. Useful before uploading images to websites, email, or documents.
- Format conversion — convert between JPEG, PNG, and WebP.
How to Convert WebM to MP4 (Step by Step)
Open the Media Converter
Navigate to webdesks.app/#mediaconv or click the file-cog icon in the WebDesks sidebar.
Select the Video tab
Click the Video (WebM → MP4) tab at the top of the converter panel to activate video conversion mode.
Add your WebM file
Drag and drop your .webm file onto the drop zone, or click the zone to browse for it. Your file is loaded locally — it never leaves your device.
Choose output format
Select MP4 (H.264), WebM (VP9), or Animated GIF from the output format dropdown.
Convert and download
Click Convert. A progress bar shows the conversion status (FFmpeg loads on first use, which takes a moment). When complete, click Download to save the converted file.
Privacy note: The entire conversion happens in your browser using WebAssembly. Your video file is never uploaded to any server. The FFmpeg library is the only external resource loaded — the file processing is 100% local.
Why WebM Files Need to Be Converted
WebM is a video format developed by Google, optimised for web streaming. Chrome, Firefox, and Edge record screen captures in WebM by default (including recordings from the WebDesks Screen Recorder). However:
- Apple devices don't natively support WebM — Safari and QuickTime can't play WebM files without additional plugins.
- Most video editors don't import WebM — Premiere Pro, Final Cut Pro, DaVinci Resolve, and iMovie all prefer H.264 MP4.
- Email attachments are better in MP4 — email clients and messaging apps universally support MP4 playback.
- Social platforms prefer MP4 — Twitter, LinkedIn, YouTube, and TikTok all accept MP4 more reliably than WebM.
Output Format Guide: MP4, WebM, or GIF?
MP4 (H.264) — Best for sharing and editing
Choose MP4 when you need the widest compatibility. Works everywhere — Apple, Windows, Android, social media, video editors. Ideal for screen recording deliverables, tutorial videos, and client-facing content.
WebM (VP9) — Best for web embeds
Choose WebM if you're embedding the video on a website and need a smaller file size than MP4. VP9 encoding gives better compression than H.264 for the same quality. Works natively in Chrome and Firefox.
Animated GIF — Best for documentation and quick sharing
Choose GIF for short clips (under 15 seconds) that need to play automatically without user interaction — perfect for README files on GitHub, Notion pages, Jira tickets, and Slack messages. Note: GIFs have no audio and larger file sizes than video formats.
How to Resize and Compress Images
Switch to the Image Resize / Compress tab for image processing:
- Click the Image tab in the Media Converter.
- Drop one or more image files onto the drop zone (JPEG, PNG, WebP supported).
- Set your target dimensions (width × height in pixels) or a percentage scale.
- Adjust the quality slider to control the output file size.
- Choose the output format (JPEG, PNG, or WebP).
- Click Convert, then download each processed image.
All image processing runs locally in your browser. No images are uploaded to any server — critical for photographs of people, confidential documents, or commercially sensitive images.
Media Converter vs. Online Video Conversion Sites
| Feature | WebDesks Media Converter | CloudConvert / Zamzar / etc. |
|---|---|---|
| Files uploaded to server | ✔ No (local only) | ✘ Yes (server upload) |
| Account required | ✔ No account needed | ✘ Often required |
| File size limit | ✔ No enforced limit | ✘ Often 100MB–2GB cap |
| Privacy | ✔ Files never leave device | ✘ Server-processed |
| Speed | ~ Depends on device CPU | ✔ Server-accelerated |
| Cost | ✔ Free | ✘ Often freemium/paid |
| Works offline | ✔ Yes (PWA + WASM) | ✘ Requires internet |
Frequently Asked Questions
Is the WebM to MP4 converter really free?
Yes. The WebDesks Media Converter is completely free with no account, subscription, or conversion limits.
Is there a file size limit?
There's no enforced file size limit. However, very large files (multi-gigabyte) may cause performance issues depending on your device's RAM and CPU. For files over ~2GB, a dedicated desktop converter like HandBrake may be faster.
Why does the first conversion take longer?
FFmpeg.wasm (the WebAssembly version of FFmpeg) needs to load on first use — this takes 10–30 seconds depending on your connection speed. Subsequent conversions in the same session are much faster as the library is already loaded.
Does it convert other video formats (not just WebM)?
The current input focus is WebM files. This covers the most common use case (browser screen recordings). For other format conversions (MOV, AVI, MKV), a desktop tool like HandBrake or VLC offers broader format support.
Can I use the image resizer for batch processing?
Yes. The image mode accepts multiple files in a single drop. Each image is processed separately with the same settings — useful for resizing a batch of product photos or screenshots to consistent dimensions.