3.1.4.1 Request to Retrieve Content Information

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This event causes the client to send a LinkViewerToMacConnect (section 2.2.4.17) message to the server. An application asks the client for information on multimedia content most often under the following common scenarios:

  • A media player application that intends to play multimedia content that will be streamed from a server. The media player knows the URL to the content, and it might already know at what time position and at what rate it intends to play the content. However, before it can start playing the content, it needs to retrieve information on what audio and video streams (2) are included in the content, what decoders are needed to decompress the content, and so on.

  • A cache that already has a copy of the content but wants to retrieve information on the content from the server to determine if the cached copy is still fresh.

  • A server or intermediate device, such as a noncaching proxy that asks for information on behalf of another client.

The higher layer MUST provide the URL that is specified in all requests that the client sends. The value of the Server-URL variable in the abstract data model MUST be set to this URL.

The client MUST perform the initialization of the protocol, as specified in section 3.1.3.

The higher layer SHOULD specify if the client needs to connect to an MMS proxy server, and if so, provide the IP address of the MMS proxy server and the port number on which the MMS proxy server receives UDP and TCP packets. The Proxy-Address variable MUST be set to the IP address of the proxy server, if any.  The Proxy-Port variable MUST be set to the port number on which the proxy server receives UDP and TCP packets, if any.

If the value of the Proxy-Port variable is not 0, then the client MUST establish a TCP connection to the proxy, using the IP address given by the value of the Proxy-Address variable and the port number given by the value of the Proxy-Port variable. Otherwise, the client MUST establish a TCP connection to the server by using the IP address and port number obtained by parsing the value of the Server-URL variable. Next, the client MUST send the LinkViewerToMacConnect (section 2.2.4.17) message to the server, as specified in section 3.1.4.1.1.