Which audio formats a browser plays decides what arrives on a page and which format an audio sample needs. The check asks this browser directly: the audio element through canPlayType, Media Source Extensions for streaming and MediaRecorder for recordings. Nothing is loaded or sent, these are plain queries.
| Format | MIME type | Audio element | MediaSource |
|---|
“Probably” means, according to the HTML Standard, that the browser is confident; “maybe” is the careful answer the standard recommends as long as support can be neither confirmed nor ruled out.
| Format | MIME type | MediaRecorder |
|---|
MediaRecorder concerns recordings in the browser, for example a voice memo on a page. Without that interface every row reads “unknown”.
According to the HTML Standard, canPlayType on the audio element answers with an empty string when the browser knows it cannot render the type, with “maybe” when it can neither confirm nor rule out support, and with “probably” when it is confident.
MediaSource.isTypeSupported only states that a SourceBuffer can be created for this type; the specification points out that a later addSourceBuffer can still fail when the resources are missing.
MediaRecorder.isTypeSupported names the containers and codecs this browser can record into. That list often differs from the list of formats it plays.
Sources: HTML Standard, 4.8.11.3 MIME types · Media Source Extensions
The answers apply to this browser on this device, including the operating system and its hardware decoders; another device can answer differently. What is checked are the browser's own statements, not the playback itself.