What is the purpose of the source element inside video or audio elements?

• A. It defines the default playback speed.
• B. It provides alternative media sources for the browser to choose the first supported one.
• C. It embeds metadata about the track.
• D. It controls the volume.

Answer: (B)

The source element inside video or audio is used to offer alternate media files in different formats so the browser can pick one it can play. Providing multiple sources in a media element helps maximize compatibility across browsers and devices, since not all browsers support the same codecs or container formats. The browser looks through the listed sources in order and starts playing the first one it can decode, using the type or codec information to decide. If none of the provided sources are playable, the browser can fall back to the content inside the video or audio element (like captions or fallback text). This is different from controlling playback speed, which is handled by playback settings, or from embedding metadata, which is handled by separate elements or attributes.