Converters WebM to MP4 converter
Convert WebM recordings and downloads to MP4 so phones, editors and social platforms will accept them.
Anything but Original forces a re-encode.
Quality, if a re-encode is needed
Drag files here, or
Converted to MP4 on your device. The converter itself is a 9.8 MB download, once.
Ready. Runs locally on your device.
Your files stay on your device. The tool works directly in your browser, using your device to process your files. Nothing is sent to our servers, and we never receive, store, or see your files or figures.
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Cite this page
Reembun. (2026, August 12). WebM to MP4 converter. https://reembun.com/webm-to-mp4
How to use it
Add the WebM
Drop in the file, or several if you have a batch of recordings.
Wait for the engine once
The converter downloads on the first run and stays cached for later.
Convert
MP4 is already the target. WebM usually carries VP8 or VP9 video, which MP4 does not take, so the video is re-encoded.
Download the MP4
The output plays in editors and on hardware that refuses WebM, which is normally the reason for the conversion.
Why this one genuinely has to re-encode
Most conversions on this site are a repackaging job: the video stream is copied from one container into another and nothing is compressed twice. WebM is the exception, and it is worth understanding why.
WebM is a container built around VP8 and VP9, Google’s royalty-free video codecs. MP4 is built around H.264. The two families exist in deliberate opposition to each other, since VP8 and VP9 were created specifically to avoid H.264’s patent licensing, and MP4 has no provision for carrying either of them.
So there is no shortcut. Every frame is decoded from VP9 and compressed again as H.264. That is real computation, and with the engine running on a single core it takes roughly one to three minutes per minute of video on a laptop.
Expect a bigger file, and that is normal
VP9 compresses better than H.264, typically by 30-50% at matched quality. Converting to MP4 means giving that efficiency up.
| Source | Typical result |
|---|---|
| 10 MB WebM screen recording | 12-18 MB MP4 |
| 50 MB VP9 clip | 60-90 MB MP4 |
If the MP4 comes out smaller than the WebM, quality was lost somewhere: either the quality setting is low, or the resolution was reduced. Set quality to High if that matters.
Where WebM files come from
Almost always, from something that recorded video using a browser:
- Browser screen recorders and in-page recording tools. The MediaRecorder API writes WebM and nothing else.
- WhatsApp Web and several other web messengers.
- YouTube downloads, where VP9 is the format served for most resolutions.
- OBS and Discord under certain presets.
All of these play perfectly in any browser and are then rejected by Instagram, TikTok, Premiere, iMovie, Windows Photos and every smart TV. That mismatch is what this page exists for.
Getting it done faster
A re-encode’s cost is dominated by pixel count, so the resolution setting is the lever that matters:
- Original is right for anything you are keeping.
- 1080p is enough for any upload target and cuts a 4K recording’s work by three quarters.
- 720p is plenty for a screen recording headed to a chat or a bug report, and finishes several times faster.
The quality setting matters less than people assume. Balanced is transparent on screen recordings and flat graphics, which is what most WebM files contain.
Nothing is uploaded
The conversion runs on your machine using FFmpeg compiled to WebAssembly. Screen recordings in particular tend to contain more than their owner remembers, such as open tabs, email subject lines and customer names in a CRM, which makes them a poor thing to hand to an unknown server.
Common questions
Why does WebM to MP4 always take longer than other conversions?
Because it cannot be avoided. WebM holds VP8 or VP9 video, and MP4 cannot carry either, so there is no legal way to copy the stream across. Every frame has to be decoded and compressed again as H.264. That is real work, and on a single processor core it takes roughly one to three minutes per minute of video.
Will the MP4 be larger than the WebM?
Usually yes, sometimes by a lot. VP9 is a more efficient codec than H.264, so matching its quality takes more bits. That is the price of a file that plays everywhere. If size matters more than compatibility, keep the WebM.
Why can I not upload my WebM to Instagram or Premiere?
WebM was designed for playback inside web browsers, and that is where its support ends. Social platforms, phone galleries, editing software and most TVs do not accept it, even though every browser plays it perfectly.
Where do WebM files come from?
Browser screen recorders, most in-page recording tools, WhatsApp Web, some Discord and OBS presets, and YouTube downloads. Anything that captured video using a browser API produced WebM, because that is the format browsers can write.
Can I make the conversion faster?
Yes. Drop the resolution to 720p or 480p in the tool. Fewer pixels means proportionally less work, and for a screen recording headed to a bug report or a chat, 720p is usually indistinguishable anyway.
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