WebM vs MP4: Which Format Is Smaller and When It Matters

For the same visual quality, WebM is usually smaller than MP4 , often by 25-50%, because the modern codecs inside WebM (VP9 and AV1) compress more efficiently than the H.264 codec that powers most MP4 files. The catch: MP4 plays everywhere with zero fuss, while WebM is built for the web and can stumble on older devices, Safari, and some editing apps. Which one wins depends entirely on where the video needs to play.

Container vs codec, the part everyone confuses

WebM and MP4 are containers, not codecs. A container is a wrapper that holds the video stream, audio stream, subtitles, and metadata together in one file. The actual compression is done by the codec inside that wrapper, and that is what controls file size.

• MP4 almost always carries H.264 video and AAC audio. It can also hold newer H.265 (HEVC), though that is less common online.
• WebM carries VP9 (or older VP8) and increasingly AV1, paired with Opus or Vorbis audio.

So when people ask "is WebM better than MP4," they are really comparing VP9/AV1 against H.264. If you want a deeper look at how codecs and containers fit together, see what a codec is and why it matters.

Which format is actually smaller

The codecs WebM uses were designed years after H.264 and squeeze more detail into fewer bits. Here is the rough efficiency ranking from biggest files to smallest, at matched quality:

• VP8 / H.264: roughly the same generation, similar sizes.
• VP9 (WebM) / H.265: about 30-50% smaller than H.264 for the same look.
• AV1 (WebM): another 20-30% smaller than VP9, the most efficient mainstream codec today.

Google reports that VP9 cuts bandwidth significantly versus older codecs, which is exactly why YouTube serves it. So for the question of WebM vs MP4 file size, WebM wins almost every time, as long as you compare a modern WebM codec to standard H.264 MP4.

Real-world file size comparison

Here is a typical 60-second 1080p clip exported at visually similar quality. Numbers vary with content (fast motion costs more bits), but the pattern holds:

The size of any of these is driven by bitrate, the amount of data spent per second of video. If you want to understand the lever that actually controls size, read how video bitrate controls file size and quality. The broader strategies for shrinking video without wrecking it are covered in video compression 101.

Browser and device support

Smaller files mean nothing if the video refuses to play. This is where MP4 still dominates.

• MP4 (H.264) : plays on essentially everything made in the last 15 years, every browser, phone, smart TV, and editing app.
• WebM (VP9) : supported in Chrome, Firefox, Edge, and Android. Safari added VP9 support starting with macOS Big Sur, but older Apple devices may fail.
• WebM (AV1) : growing fast in modern browsers, but hardware decoding is only on recent chips, so older devices decode in software and can stutter.

You can check the live picture on caniuse.com's WebM support table. The safe move for maximum reach is to offer both: WebM first for browsers that support it, MP4 as the fallback. The HTML5 <video> element lets you list multiple sources and the browser picks the first one it can play.

<video controls>
  <source src="clip.webm" type="video/webm">
  <source src="clip.mp4" type="video/mp4">
</video>

When to use WebM

Pick WebM when bandwidth and load speed matter more than universal compatibility:

• Embedding video on a website where smaller files speed up page loads and cut hosting bandwidth.
• Background videos and looping animations that need to be tiny and never leave the browser.
• Replacing animated GIFs, since a WebM is a fraction of the size of the same loop as a GIF.
• Streaming to known-modern audiences where you control or expect current browsers.

When to use MP4

Reach for MP4 when the video has to "just work" anywhere:

• Sharing with clients or coworkers who might open it on any device, including older iPhones.
• Uploading to social platforms, most of which prefer or require MP4 (check the limits in every major platform's file size cheat sheet).
• Video editing, since H.264 MP4 is the most widely accepted import format in editors.
• Email or messaging, where compatibility beats squeezing out the last megabyte. Related limits live in why email attachments still have size limits.

How to open a WebM file

If someone sent you a WebM and it won't open, you have a few easy paths:

• Any modern browser: drag the file into a Chrome, Firefox, or Edge tab and it plays.
• VLC Media Player: the free, cross-platform player handles WebM natively on Windows, Mac, and Linux.
• Convert it to MP4 if you need it in an editor or an unsupported device.

Windows Media Player and older versions of QuickTime often won't open WebM without extra codecs, which is the usual reason the file "won't play." When that happens, converting to MP4 is the fastest fix.

Make your WebM files even smaller

Already chose WebM for its file size advantage in the WebM vs MP4 trade-off? Our free WebM compressor re-encodes with VP9 or AV1 and a quality slider, so you can shrink web video without touching the original quality you need.

Compress a WebM →