WebM to MP4 converter
FileReshape's WebM to MP4 converter re-encodes the VP8, VP9 or AV1 picture of a WebM video as H.264 and the Opus or Vorbis sound as AAC, and saves an MP4, using FFmpeg in your browser. The video is not uploaded. Because the picture is encoded again on your device, it takes roughly one to five minutes per minute of video.
Did a file not convert correctly? E-mail [email protected], ideally with a small sample file, and it will be fixed.
Key facts
- Input: WebM (.webm). Output: MP4 (.mp4).
- Your files are not uploaded: the work is done in your browser, on your own device.
- File size: up to 2 GB per file (the limit of the browser's WebAssembly memory).
- Needs a current browser (Chrome, Edge, Firefox or Safari) on a computer, tablet or phone; nothing to install.
- Free to use, with no sign-up.
WebM to MP4: why convert
WebM is what Chrome's and Firefox's built-in recorders, browser extensions for screen capture, Loom-style tools, some online meeting recordings and many downloaded web videos produce. It plays in a browser, but iMovie, Premiere Pro, PowerPoint on a Mac, WhatsApp, Instagram and many smart TVs and upload forms refuse it. MP4 with H.264 picture and AAC sound is the combination every device and program accepts. This converter reads the WebM in your browser, encodes the picture as H.264 at high quality and the sound as AAC, and puts both into an MP4 that starts playing straight away when it is put on a website. Screen recordings with private documents, faces or customer data never leave your computer.
How to convert WebM to MP4
- Drop the WebM file in the box, or click to choose it.
- Check the duration, picture size and codecs shown.
- Click Convert to MP4, wait for the progress to reach 100 %, and save the MP4.
What changes when you convert
Re-encoding takes time
VP8, VP9 and AV1 cannot be copied into a normal MP4 that every device plays, so the picture is encoded again. On a recent laptop a minute of 1080p takes about two to five minutes; screen recordings with little movement are faster. The page shows the progress and the time left.
Variable frame rate
Browser recordings often have an uneven frame rate, which some video editors handle badly. FFmpeg keeps picture and sound in step in the MP4, which is the format editors and phones expect.
Transparent WebM
WebM can hold a transparent background (VP9 with alpha), used for stickers and overlays. H.264 MP4 has no transparency, so those areas become black.
Audio-only WebM
Some voice messages and recordings are WebM files with only sound. They have no picture to put in an MP4; use the MP3 converter for those instead.
About the formats
WebM
WebM is an open video format made by Google for the web in 2010. The picture is compressed with VP8, VP9 or AV1 and the sound with Opus or Vorbis. Browser screen recorders, Chrome's MediaRecorder, many downloaded web videos and some messaging apps save WebM, but iPhones, older Windows programs, video editors and social networks often do not accept it.
- WebM is based on the Matroska (MKV) container, limited to web-friendly codecs.
- VP9 makes files about as small as H.265 and is what YouTube streams in most browsers.
- Safari plays WebM since version 14.1 (2021), but many Apple apps still refuse it.
- A WebM file can also hold only sound, usually Opus: voice messages in some apps are audio-only WebM.
MP4
MP4 (MPEG-4 Part 14) is the most common video file format. Phones, cameras, YouTube, WhatsApp and every computer and TV use it. An MP4 is a container: the picture inside is usually compressed with H.264 or H.265 (HEVC) and the sound with AAC, and the same file can also hold subtitles, chapters and a cover image.
- The format was standardised in 2003 and is based on Apple's QuickTime format, which is why MP4 and MOV files are so alike.
- H.264 video with AAC sound plays on practically every device made in the last 15 years.
- A minute of phone video in 1080p is typically 100–200 MB; in 4K it is often 350–500 MB.
- The "faststart" layout puts the index at the beginning, so a video can start playing before it is fully downloaded.
Frequently asked questions
Is my WebM file uploaded?
No. FFmpeg runs in your browser tab and the new MP4 is made on your own device. Nothing is sent to a server.
Will the quality drop?
Very little. The picture is encoded with H.264 at a high quality setting (CRF 21). The MP4 is often a bit larger than the WebM, because VP9 compresses more efficiently than H.264.
Why does my WebM not open on my iPhone?
iPhones only play WebM in Safari on web pages, not in the Photos app or most other apps. MP4 with H.264 opens everywhere on Apple devices.
Can I make the MP4 smaller?
Yes. Run the MP4 through the video compressor afterwards, which can also lower the resolution to 720p or 480p.