ASX contains the URL corresponding to the media content. When we make a hyperlink in HTML to contact ASX, the browser will directly send the content of ASX to the media player, and the media player will use the corresponding protocol to open the multimedia information stream or multimedia file at the specified location according to the information of ASX file.
The main reason for using ASX file to redirect streaming media information is that common browsers can't directly support MMS, which is the protocol for playing streaming media information, so we use ASX file.
After using the ASX file, when the browser finds the connection related to ASX, it knows that it needs to use the media player to play the streaming media information, so it will start the Meida player, and the media player can play the streaming media information using the MMS protocol.
Source: Teacher Apple.