WebM to MP4 Converter
Convert WebM videos to MP4 format instantly in your browser. Secure, private, and free. No server uploads required.
Drag & Drop WebM file here
About
This WebM to MP4 Converter provides a secure, client-side solution for transforming modern WebM video files into the widely compatible MP4 format. Unlike server-based converters that require large file uploads, this tool processes your video data locally using your browser's native MediaRecorder API.
The tool utilizes a re-encoding pipeline where Vin (the WebM source) is decoded and immediately re-encoded into Vout (the MP4 container) using the H.264 codec. This method ensures that your data never leaves your device, providing maximum privacy and zero latency dependent on internet speed.
Note on Performance: Because this tool uses the browser's internal rendering engine, conversion speed correlates with video duration and playback speed. We utilize a × speed modifier to accelerate the process where possible.
Formulas
The conversion process relies on the browser's ability to transcode media streams in real-time. The efficiency can be approximated by the playback rate factor:
Where Dvideo is the duration of the source video, Rspeed is the playback rate (e.g., 2.0x), and tmux is the overhead time for blob assembly.
Reference Data
| Feature | WebM (Source) | MP4 (Target) |
|---|---|---|
| Container Format | Matroska (Subset) | ISO Base Media File Format |
| Video Codec | VP8 / VP9 / AV1 | H.264 (AVC) / H.265 (HEVC) |
| Audio Codec | Vorbis / Opus | AAC / MP3 |
| Browser Support | Chrome, Firefox, Edge | Universal (All Browsers & OS) |
| Transparency | Supported (Alpha Channel) | Not Supported (Usually) |
| Compression Efficiency | High (Modern) | Medium-High (Standard) |
| MIME Type | video/webm | video/mp4 |