WebM vs. MP4: Which Is Better for File Size?

When you're trying to shrink a video, the format choice matters. WebM (VP9) and MP4 (H.264) are the two most common formats for web and sharing. Both can compress video well, but they differ in efficiency, compatibility, and use cases. Here's a practical comparison to help you choose.

Compression Efficiency: WebM Often Wins

VP9, the video codec inside WebM, typically achieves 20–50% better compression than H.264 at the same quality level. That means a WebM file can be 20–50% smaller than an MP4 for the same visual quality. For a 100 MB file, that could mean 50–80 MB in WebM. If file size is your top priority and you're targeting web playback, WebM is the better choice.

Compatibility: MP4 Wins Everywhere

H.264 in MP4 is supported everywhere: every phone, tablet, smart TV, game console, and browser. WebM is supported in Chrome, Firefox, and Edge, but Safari's support has been inconsistent. Apple devices often prefer MP4. If you're sharing via email, Discord, WhatsApp, or other platforms, MP4 is the safer bet. Media Shrinker outputs MP4 for maximum compatibility.

When to Use Each

Use WebM when you're embedding video on your own website and can serve multiple formats (e.g., WebM for Chrome, MP4 for Safari). Use MP4 when you're sharing files—email, messaging, social media—or when you need universal playback. For most users, MP4 is the right default. You can always re-encode to WebM later if you need smaller files for a specific web project.

Encoding Speed

H.264 encodes faster than VP9 in most cases. VP9's better compression comes at the cost of longer encoding time. For a browser-based tool like Media Shrinker, H.264 is the practical choice—it keeps processing fast and the output compatible. The trade-off in file size is usually acceptable for the use cases we target (sharing, Discord, email, etc.).