canPlayType

canPlayType is a method of the HTMLMediaElement interface that allows a script to query whether the user agent can play a given media type. It is available on media elements such as HTMLVideoElement and HTMLAudioElement. The method accepts a single string parameter that identifies a MIME type and, optionally, a list of codecs. For example: video.canPlayType('video/mp4; codecs="avc1.42E01E, mp4a.40.2"').

The return value is a string and can be "probably", "maybe", or an empty string "". "Probably" indicates the browser believes playback is likely for the specified type; "maybe" indicates possible playback under certain conditions; an empty string means the type is not supported by the user agent.

Usage of canPlayType is common for progressive enhancement, allowing a page to select a source that is most likely to play without attempting to load and play content upfront. However, canPlayType is not a guarantee of playback. It does not account for network conditions, licensing, DRM, or hardware constraints, and results can vary between browsers and versions. Therefore, developers often pair canPlayType checks with actual playback tests or provide multiple source options as fallbacks.

Example usage: create a video element and query canPlayType for different formats to decide which source to supply, or to decide whether to show a format selector to the user.

Related concepts include the HTMLMediaElement interface and the HTMLVideoElement and HTMLAudioElement types, which expose canPlayType as part of their capability detection.