HTMLMediaElement.canPlayType()

The HTMLMediaElement method canPlayType() reports how likely it is that the current browser will be able to play media of a given MIME type.

canPlayResponse = audioOrVideo.canPlayType(mediaType);

mediaType

A DOMString containing the MIME type of the media.

A DOMString indicating how likely it is that the media can be played. The string will be one of the following values:

probably

Media of the type indicated by the mediaType parameter is probably playable on this device.

maybe

Not enough information is available to determine for sure whether or not the media will play until playback is actually attempted.

"" (empty string)

Media of the given type definitely can't be played on the current device.

var obj = document.createElement('video');
console.log(obj.canPlayType('video/mp4')); // "maybe"

• The interface defining it, HTMLMediaElement.
• MediaCapabilities in the Media Capabilities API
• Handling media support issues in web content
• Guide to media types and formats on the web