WebM to MP4 (H.264) - Online Video Converter
Convert WebM to MP4 (H.264) online. Private, client-side - no uploadrequired. Batch conversion, quality presets, codec control.
About WebM to MP4 (H.264)
WebM pairs VP9 video with Opus audio and supports an alpha channel for transparent overlays. MP4 re-encodes the picture as H.264 with AAC sound for universal playback across phones, browsers, and editors. H.264 has no alpha channel, so transparency is dropped; composite overlays over a background first. VP9 needs full decoding before re-encoding, so long files take a while. Apple editors accept the result directly, which makes this path useful before editing round-trips.
Why convert WebM to MP4 (H.264)?
- Smaller files with MP4 lossy compression.
- Keep animation and transparency where supported.
- Private, no upload - runs in your browser.
WebM vs MP4 (H.264)
| Animation | Yes | Yes |
|---|---|---|
| Transparency | Yes | No |
| Compression | lossy | lossy |
| Typical use | WebM pairs VP9 video with Opus audio and supports an alpha channel. | MP4 pairs H.264 video with AAC audio in the ISO base media container. |
When not to convert WebM to MP4 (H.264)
- Skip MP4 for archival masters: lossy compression discards detail, so keep the WebM original.
- Flatten transparency first: MP4 has no alpha channel, so composite WebM over a background color.
Limits
Starting point: WebM - VP9 video with Opus audio and alpha support. Apple editors accept it unevenly; keep MP4 for editing round-trips. H.264 has no alpha channel, so transparency is dropped. Encode MP4 (H.264 / AAC) from WebM at a bitrate near the source, and confirm the audio track before converting.
How conversion works
Conversion runs entirely in your browser with FFmpeg WASM. Files never leave your device.