The source element allows authors to specify multiple media resources for media elements. It does not specify anything on its own.
The src attribute gives the address of the media resource. The value must be a valid URL. This attribute must be present. Note that dynamically manipulating this value after the page has loaded has no effect on the containing element; instead, change the src attribute of that element (audio or video) instead.
The type attribute gives the type of the media resource, to help the user agent determine if it can play this media resource before fetching it. If specified, its value must be a valid MIME type. The codecs parameter may be specified and might be necessary to specify exactly how the resource is encoded.
The media attribute gives the intended media type of the media resource, to help the user agent determine if this media resource is useful to the user before fetching it. Its value must be a valid media query.
<source src="foo.webm" type="video/webm; codecs="vp9, opus"">
Your browser does not support the <code>video</code> element.
This example specifies that a video object with playback controls should be drawn, playing the file "foo.ogg". The type is specified as "video/ogg", and the source element also specifies that the video file uses the Dirac and Speex codecs.