WebM to MP4 converter
Drop in a WebM file and get a playable MP4 back. The conversion runs inside this page, so nothing is uploaded and there is no queue to wait in.
Drop a WebM file here, or choose one
Converted on your device · nothing is uploaded · no size limit
- No upload — files stay on your device
- No signup and no watermark
- No file size limit
WebM is the format the web hands you when you save a video from a browser, pull a clip out of a messaging app, or export from certain screen recorders. It is an excellent delivery format and a frustrating file to actually own, because most of the software on your computer and nearly everything on an iPhone refuses to open it.
Converting to MP4 fixes that in one step. MP4 carrying H.264 video and AAC audio is the closest thing digital video has to a universal format: it plays on every phone, every desktop operating system, every smart TV, and it imports cleanly into every editor worth using.
How to convert WebM to MP4
- Choose your file. Drag a WebM file onto the strip above, or click it to browse. The first file also loads the converter itself, which takes a few seconds.
- Wait for the bar to fill. Encoding runs on your own processor. A one-minute 1080p clip usually takes under a minute; keep the tab open while it works.
- Download the MP4. The finished file appears as a download button and saves straight to your device.
Why convert WebM to MP4
Your file plays on Apple devices again
Safari and the iOS Photos app have never supported WebM properly. A WebM sent to an iPhone typically arrives as a file the recipient cannot open at all. An MP4 opens by tapping it.
Video editors will accept it
Premiere Pro, Final Cut, DaVinci Resolve and CapCut all deal with H.264 in an MP4 wrapper natively. Dropping a WebM into a timeline usually produces either an import error or audio with no picture.
Uploads stop failing
WhatsApp, most CRM and e-learning platforms, older content management systems and plenty of client upload portals accept MP4 and silently reject WebM.
Hardware decoding saves battery
Phones and laptops decode H.264 on a dedicated chip. VP9 inside WebM often falls back to software decoding, which runs the processor harder and drains the battery faster on long videos.
How the two formats differ in practice
| WebM | MP4 | |
|---|---|---|
| Container | WebM (Matroska-derived) | MP4 (ISO base media) |
| Usual video codec | VP8 or VP9 | H.264 / AVC |
| Usual audio codec | Vorbis or Opus | AAC |
| Safari and iOS | Unreliable to unsupported | Supported everywhere |
| Editing software | Frequently rejected | Accepted natively |
| File size at equal quality | Roughly 20–30% smaller | Larger, but universally playable |
Doing it yourself with ffmpeg
If you convert files regularly, or need to process a whole folder, run it locally instead. This is the same operation the tool above performs:
ffmpeg -i input.webm -c:v libx264 -crf 23 -preset veryfast -c:a aac -b:a 192k -movflags +faststart output.mp4Every flag is explained in the guide to the ffmpeg command.
Questions
Is there a file size limit?
There is no limit imposed by this site, because there is no server doing the work. The practical ceiling is your own device's memory — files up to about 2 GB convert reliably on a desktop browser, and phones manage a few hundred megabytes comfortably.
Does converting WebM to MP4 lose quality?
The video is re-encoded, so a small amount of quality is discarded. The default setting used here targets visually transparent output, meaning the difference is not noticeable in normal viewing. Converting a file that has already been compressed several times will show more degradation than converting a fresh export.
Will the MP4 be bigger than the WebM?
Usually, yes, by roughly a quarter. VP9 is a more efficient codec than H.264, so matching its quality in MP4 costs extra bytes. That trade buys compatibility with every device you own.
Are my videos uploaded to a server?
No. The converter is compiled to WebAssembly and runs in your browser tab. Your file is read from disk into the page's memory and written back out as a download. It never travels over the network, which is also why the conversion starts instantly rather than queueing.
Why is my video taking a long time?
Encoding speed depends on your processor, the resolution and the length of the clip. A one-minute 1080p file takes roughly 30 to 60 seconds on a modern laptop. Long or 4K files take proportionally longer. The tab must stay open, but you can work in other tabs meanwhile.
Does the audio come across?
Yes. Opus or Vorbis audio is re-encoded to AAC at 192 kbps and muxed into the MP4. If your source has no audio track, the output simply has none either.
Can I convert several files at once?
Run them one after another in the same tab. The converter stays loaded after the first file, so every file after the first starts immediately.