WebM to MP3 Converter

WebM files carry their sound as Opus or Vorbis, which many car stereos, older phones and music apps do not play. This converter decodes the WebM's audio and saves it as an MP3, the format every device understands. It also takes audio-only .weba files saved from browsers and voice recorders. Conversion runs in your browser — usually with the browser's own decoder, otherwise with the ffmpeg engine — and nothing is uploaded.

How to use this tool

1. Choose one or more .webm or .weba files.
2. Pick the MP3 bitrate (192 kbps for music, 128 kbps or mono for speech).
3. Optionally set a start and end time.
4. Press Calculate and download the MP3s.

Formula

MP3 size ≈ bitrate (kbps) × 125 × seconds

Opus is decoded to PCM at 48 kHz and encoded with LAME; the MP3 keeps 48 kHz unless the browser cannot decode the file, in which case ffmpeg keeps the source rate. Opus is more efficient than MP3, so a 96 kbps Opus track needs around 160–192 kbps as MP3 to sound the same.

Example

A 12-minute WebM lecture with 64 kbps Opus speech, converted to 128 kbps mono MP3: 128 × 125 × 720 = 11.5 MB. At 192 kbps stereo it would be about 17 MB with no audible gain for speech.