OneTaskBy Tim King · Updated
MP4 to WebM
VP9 Video and Opus Audio for Smaller, Royalty-Free Embeds on Websites
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How the MP4 To WebM works
This MP4 to WebM converter turns an MP4 into a WebM with VP9 video and Opus sound. WebM is the open, royalty-free format of the web: every current browser plays it in a video tag, and VP9 usually gives a smaller file than H.264 at the same quality. The conversion runs on your device and nothing is uploaded.
MP4 to WebM: when it is worth it
- Web pages. A WebM source in a video tag plays in Chrome, Edge, Firefox and Safari 14.1 or later. Serving WebM first and MP4 as a fallback is common practice for background and product videos, because the WebM is usually smaller.
- Open formats. VP9 and Opus are royalty-free. Some projects, such as Wikipedia, accept only open formats.
- Smaller files. VP9 typically needs 20 to 40 percent fewer bits than H.264 for the same picture, depending on the content.
Keep the MP4 when the file is for an editor, a TV or an older iPhone. Those handle H.264 far more reliably than VP9.
How the conversion works
MP4 holds H.264 or HEVC video with AAC sound, and WebM allows only VP8, VP9 or AV1 with Opus or Vorbis. So both streams are re-encoded. The page reads the MP4 with Mediabunny, an open-source media library. It decodes and encodes with WebCodecs, the browser's interface to the device's video hardware. VP9 encoding is slower than H.264 on most devices because fewer chips encode it in hardware. Expect anything from real time to a few times faster.
Getting the size right
This page aims for visual quality rather than a size. For a WebM under a fixed size, such as an upload limit, use the video compressor. For a short silent loop, a WebM is far smaller than a GIF, but if the target only accepts GIF, use video to GIF.
FAQ
Does Safari play WebM?
Safari 14.1 and later play VP9 WebM on a Mac, and iOS 15 and later on iPhone and iPad. Older Apple devices need the MP4, so offer both files on a web page when visitors may use old iPhones.
Why is VP9 encoding slower than MP4?
Most graphics chips encode H.264 in hardware, but fewer encode VP9, so the browser may fall back to software encoding. It still runs on your device; it just takes longer on long clips.
Will the WebM be smaller than the MP4?
Usually, though not always. A file that was already heavily compressed may come out about the same size. The results panel shows both sizes, so you can keep whichever file is smaller.
Is the video uploaded?
No. Everything happens in this browser tab and the file never leaves your device. The page only needs the internet to load itself and the converter library, and the finished file is saved straight from memory to your downloads.
See also: all Audio & Video tools, Units, Images, Documents, Data & Code.
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