WebM to MP4 Converter
To convert WebM to MP4 here, drop the file on the page: the VP8 or VP9 video becomes H.264 and the Opus or Vorbis audio becomes AAC, and nothing is uploaded. Every frame is decoded and compressed again, so it takes longer than moving H.264 into a new container.
- Free
- No sign-up
- No watermark
- Runs in your browser
Loading the tool.
Why a WebM is always re-encoded
A true WebM file can hold only VP8, VP9 or AV1 video with Vorbis or Opus audio. The MP4 made here holds H.264 and AAC. None of the streams in a WebM fits the MP4, so none of them can be copied, and the page decodes and compresses everything again. The table shows what happens to each part.
| Inside the WebM | What the page does | What you get in the MP4 |
|---|---|---|
| VP8 or VP9 video | Decodes it and encodes H.264 at a high quality setting | A picture that plays on phones, TVs and editing programs |
| AV1 video | The same, if your browser can decode AV1 | The same H.264 picture |
| Opus or Vorbis audio | Decodes it and encodes AAC | AAC sound |
| No audio track, as in a screen recording made without a microphone | Converts only the video | An MP4 with no sound |
| A see-through background | Does not keep it | H.264 cannot store transparency, so the MP4 has none |
| Frame size and frame rate | Leaves them unchanged | The same size and the same speed |
Re-encoding loses a little detail every time it is done, however high the quality setting is. Treat the WebM as the original and make one MP4 from it, because converting that MP4 again would add another round of loss.
How long a WebM takes to convert
A copy only moves data, but a re-encode has to decode and compress every frame, so the time grows with the length of the video and the size of its frame, and it depends on your device. A progress bar shows how far the work has come, and Cancel stops it at any moment without saving anything. On a phone the page has to stay open and in front until the conversion ends.
Where WebM files come from
Recorders that run inside a web page, such as in-browser screen capture, often save WebM, and so do many videos downloaded from the web. Phones, TVs and most editing programs ask for MP4, which is why these files need converting. Screen recordings often carry no audio, and the page handles that case without any setting.
The encoders your browser needs
To write the MP4, your browser has to be able to encode H.264 and AAC, and the page asks it before you wait. If it cannot, a sentence under the button says which codec is missing and the button stays off. A browser with no AAC encoder of its own gets a small WebAssembly one, about 1 MB, downloaded once. That is program code for the encoder, and your video is never sent anywhere.
What happens to quality and file size
The new H.264 video is encoded at a high quality setting, which keeps most of the detail. VP9 is the more efficient codec of the two, so the MP4 is often larger than the WebM it came from. The size of the result follows the encoder's quality setting and not the size of the source, so the page can only say that it may come out bigger or smaller.
Questions people ask
How do I convert WebM to MP4 without losing quality?
You cannot copy a WebM into an MP4, because the codecs differ, so some loss cannot be avoided. The page encodes the new H.264 video at a high quality setting, which keeps most of the detail. Keep the WebM as your original and make one MP4 from it, because every further conversion adds loss again.
Why does WebM to MP4 take so long?
Every frame is decoded and compressed again, and a WebM has no stream that can be copied. The time grows with the length of the video and its frame size, and it depends on your device. A progress bar shows how far it has come, you can cancel at any point, and nothing is saved if you do.
Will a WebM with a transparent background stay transparent in MP4?
No. H.264 video in an MP4 cannot store transparency, so the see-through parts of the picture are lost. If you need to keep the transparency, keep the WebM file and use it where WebM is accepted.
Why does it say my browser can't encode H.264?
The converter asks your browser which encoders it has. Some browsers and devices have none for H.264, or none for a large frame size. The page then says which codec is missing and turns the button off. It suggests trying another output format, or the latest Chrome or Edge on a computer.
What to do with a screen recording
A WebM from a browser recorder can be a talk, a demo or a call. GPT-Video turns a long recording like that into short vertical clips with captions that follow the speech. The cutting happens on our servers and uses credits.
Related
Your file is processed on your device and never uploaded.