MP4 to WebM converter

Make WebM versions of your MP4 videos for websites, web apps and HTML5 players. VP9 often keeps the same picture in a smaller file, and nothing is uploaded.

    Original
    Original
    Result
    Result

    Why use WebM on a website

    WebM is an open, royalty-free video format designed for the web. Its VP9 video codec typically produces files 30–50% smaller than H.264 at the same quality, which means faster page loads and less bandwidth for background videos, product demos and embedded clips.

    How to use it

    1. Choose your .mp4, .m4v or .mov files, or drop them on the box above.
    2. Wait while the video is encoded to VP9. The percentage shows progress.
    3. Download the .webm file.

    What you get

    • VP9 video at a quality level tuned to look the same as the original while keeping the file small. If your browser can’t encode VP9, it uses VP8 instead.
    • Opus audio, the standard for WebM.
    • The original resolution and frame rate.

    Keeping web videos small

    The codec is only part of the story. For videos on a web page, these matter as much:

    • Resolution: a background or product video rarely needs more than 1280 × 720. Halving the width and height roughly quarters the file size.
    • Length: a 10-second loop is far lighter than a 1-minute clip, and visitors seldom watch long autoplaying videos.
    • Movement: calm footage compresses much better than fast action, confetti or noise.

    Resize or trim the MP4 in your video editor first, then convert it here.

    VP9 or AV1?

    AV1 compresses about 30% better again than VP9, but it’s much slower to encode and older devices can’t decode it, which can make playback stutter on phones. VP9 is the practical choice for most websites today, which is why this converter uses it.

    Using both formats on a page

    Offering WebM with an MP4 fallback covers every browser. The browser picks the first format it can play:

    <video controls width="640" poster="poster.jpg">
  <source src="clip.webm" type="video/webm">
  <source src="clip.mp4" type="video/mp4">
</video>

    For a silent autoplaying background video, add autoplay muted loop playsinline to the video tag. Browsers only autoplay video that’s muted.

    Privacy

    Your video is encoded inside your browser using its built-in VP9 encoder and Mediabunny, an open-source media library. Nothing is uploaded, so unreleased product videos and client work stay on your computer.

    Questions

    Why does the conversion take a while?

    VP9 is an efficient but demanding codec, and most computers encode it in software. Expect it to take one to two times the length of the video on a typical laptop. Short clips for a website finish quickly.

    Will the WebM be smaller?

    Often, but not always. The converter encodes to a quality level meant to look the same as the original, so the size depends on the video. Footage straight from phones and cameras, saved at a high bitrate, usually shrinks. MP4s that are already heavily compressed, such as web downloads, can come out a similar size or larger.

    Do all browsers play WebM?

    Chrome, Edge, Firefox and Opera play VP9 WebM on every platform, and Safari does on recent versions of macOS and iOS. For the widest support on a website, offer the WebM first and the MP4 as a fallback.

    Can I make a WebM with a transparent background?

    Not from an MP4, because MP4 video has no transparency to keep.

    Last reviewed 4 November 2026