The WebM vs. MP4 Debate
If you're publishing video on the web, you'll eventually face the WebM vs. MP4 question. Both are widely used, both work in modern browsers, but they differ in meaningful ways. This comparison breaks down the key differences so you can make an informed decision for your specific use case.
At a Glance: Side-by-Side Comparison
| Feature | WebM | MP4 |
|---|---|---|
| Primary codecs | VP8, VP9, AV1 | H.264, H.265 |
| Audio codecs | Vorbis, Opus | AAC, MP3 |
| Licensing | Royalty-free, open | Patented (licensing fees) |
| Chrome support | ✅ Full | ✅ Full |
| Firefox support | ✅ Full | ✅ Full |
| Safari support | ⚠️ Partial | ✅ Full |
| Mobile support | ✅ Android | ✅ iOS + Android |
| Compression efficiency | VP9: excellent; AV1: best | H.264: good; H.265: excellent |
| Encoding speed | Slower (VP9/AV1) | Faster (H.264) |
Licensing: The Critical Difference
This is arguably the most important distinction. MP4 relies on codecs like H.264 and H.265, which are covered by patents held by industry consortia. Distributors embedding H.264 in products have historically needed to pay royalties (though free-to-end-user web streaming has had carve-outs).
WebM, by contrast, is entirely royalty-free and open. Google released VP8 and VP9 without licensing restrictions. This makes WebM the safer long-term choice from a legal and cost perspective, particularly for open-source software or large-scale deployment.
Compression and Quality
When comparing VP9 (WebM) to H.264 (MP4):
- VP9 typically produces files roughly 30–50% smaller than H.264 at equivalent visual quality
- H.265 (HEVC) narrows that gap significantly and matches VP9 in efficiency
- AV1 (the next-generation WebM-compatible codec) generally outperforms both H.265 and VP9
For streaming bandwidth savings, VP9/WebM has a real advantage over H.264/MP4. This is why YouTube defaults to VP9 when available.
Browser and Device Compatibility
MP4 with H.264 wins on raw compatibility. It plays on essentially every device and browser, including older ones. WebM is broadly supported but has notable gaps:
- Safari: Added limited WebM support in Safari 14.1+, but it's not universal across all Apple devices and OS versions
- iOS: WebM support in Safari on iOS is restricted
- Smart TVs and set-top boxes: MP4 compatibility is much more universal
Encoding Speed and Tooling
H.264 (MP4) encoding is significantly faster than VP9 (WebM) encoding. This matters if you're processing large volumes of video or encoding on-the-fly. For batch workflows or server-side processing, H.264's speed advantage can be meaningful.
That said, for pre-encoded web assets where you encode once and serve many times, the encoding time difference is less important.
When to Choose WebM
- You want to minimize bandwidth costs with better compression
- Your target audience primarily uses Chrome, Firefox, or Edge
- You're replacing GIFs with looping video animations
- You're building open-source software and want a royalty-free stack
- You're publishing on platforms that prefer or require open formats
When to Choose MP4
- You need maximum cross-device compatibility (including older iOS/Safari)
- You're producing content for download, not just streaming
- Your workflow tools are better optimized for H.264
- You're targeting smart TVs, media players, or non-browser environments
The Best Practice: Use Both
For web video, the most robust approach is to serve both formats and let the browser choose:
<video controls>
<source src="video.webm" type="video/webm">
<source src="video.mp4" type="video/mp4">
</video>This gives you WebM's efficiency where supported, and MP4's compatibility everywhere else — a true best-of-both-worlds solution.