MP4 to WebM Converter
Re-encode H.264 to royalty-free VP9 with Opus audio for HTML5 video.
Up to 50 MB per file. Sign up free to convert files up to 100 MB.
| File name | Size | Convert to |
|---|
Checking files and selected output formats.
What to expect when converting MP4 to WEBM
Measured on a 1080p H.264 MP4: 8.93 MB in, 9.73 MB out (+9%), taking 14.2s for 10 seconds of video. Expect roughly 1.5x the clip length in processing time.
Quality: Fully re-encoded from H.264 to VP9 and from AAC to Opus. One generation of loss at a fixed quality target.
Best for: HTML5 video on your own site, platforms that require an open royalty-free format.
Avoid when: you need the file to play outside a browser, most TVs, consoles and editors reject WebM.
Tip: VP9 encoding is genuinely slow: about 0.7x real time at 1080p on our hardware, so a clip much over 6 minutes will hit the processing limit. Convert short clips, or keep the MP4 and serve WebM only as a secondary source.
MP4 to WebM: open-format video for the web
MP4 typically contains H.264 video and AAC audio, while WebM uses VP8/VP9 video and Vorbis/Opus audio. VP9 achieves similar compression efficiency to H.264 but is royalty-free. The conversion fully decodes the H.264 bitstream and re-encodes with VP9 (or VP8), which is computationally expensive, expect encoding times 2-5× longer than the video duration. The audio is transcoded from AAC to Opus (preferred) or Vorbis, both of which are high-quality open codecs.
Convert MP4 to WebM for embedding video on websites that prefer open formats, for platforms that specifically require WebM, or when you need a royalty-free video format. HTML5 video elements commonly specify both MP4 and WebM sources for maximum compatibility, WebM for Firefox/Chrome, MP4 as fallback.
MP4 vs WebM: Side-by-side
Technical comparison of the two formats, useful for deciding which to use, or for confirming what changes during conversion.
| Property | MP4 | WebM |
|---|---|---|
| Full name | MPEG-4 Part 14 | WebM (Google) |
| Year introduced | 2001 | 2010 |
| Developer / standard body | MPEG | |
| MIME type | video/mp4 | video/webm |
| File extension | .mp4 / .m4v | .webm |
| Compression | H.264 or H.265 codec | VP8/VP9/AV1 video + Vorbis/Opus audio |
| Color / data depth | 8/10-bit | 8/10/12-bit |
| Max dimensions / size | Codec-dependent (up to 8K) | Codec-dependent |
| Transparency | No | Yes |
| Animation | No | No |
| Standard / specification | ISO/IEC 14496-14 | Open Web Foundation |
| Best for | Universal video compatibility, plays on every device | Web-native video, HTML5 <video> tag |
Use MP4 when
- You need universal playback on any device, ever
- You're uploading somewhere that expects MP4
- Older browsers or embedded devices are in your audience
- You want a safe single-format delivery
Use WebM when
- You control the modern-browser environment and page-weight matters
- You want to avoid patent-encumbered codecs
- You're serving HTML5 video where smaller files improve UX
- Your CDN can serve WebM alongside MP4 automatically
For a modern site where you control the audience, WebM saves bandwidth and licensing hassle. For anywhere else, MP4 remains the safe bet. If you're running video on a public website, offering both in an HTML5 picture-style pair is a common solution, browsers pick the smaller one they can play automatically.
Frequently asked questions
How to convert MP4 to WEBM without losing resolution or quality
My MP4 video won't play - will converting to WEBM fix it?
What is MP4?
How do I open MP4 files?
Should I use WebM or MP4 for my website?
<video> with multiple sources.