The HTML Inline Frame Element (<iframe>) represents a nested browsing context, effectively embedding another HTML page into the current page. In HTML 4.01, a document may contain a head and a body or a head and a frameset, but not both a body and a frameset. However, an <iframe> can be used within a normal document body. Each browsing context has its own session history and active document. The browsing context that contains the embedded content is called the parent browsing context. The top-level browsing context (which has no parent) is typically the browser window.
The HTML <track> element is used as a child of the media elements—<audio> and <video>. It lets you specify timed text tracks (or time-based data), for example to automatically handle subtitles. The tracks are formatted in WebVTT format (.vtt files) — Web Video Text Tracks.
The HTML <audio> element is used to embed sound content in documents. It may contain one or more audio sources, represented using the src attribute or the <source> element; the browser will choose the most suitable one.
Use the HTML <video> element to embed video content in a document. The video element contains one or more video sources. To specify a video source, use either the src attribute or the <source> element; the browser will choose the most suitable one.