audio/webm

A WebM file with no video track — Vorbis or Opus in the container Google carved out of Matroska for the open web. It is what MediaRecorder hands you when you capture microphone input in a browser, which is where most of these files are born. The type alone does not say which codec is inside; that is the codecs parameter's job (audio/webm; codecs=opus). The EBML signature at offset 0 is shared with Matroska proper — only the DocType element inside distinguishes a .weba from a .mka.

.weba is the official audio extension, though in the wild audio-only WebM usually ships as .webm anyway.

Defined by WebM Container Guidelines. Registry facts from the IANA media-types registry via mime-db.