3.1.4.2 Request to Retrieve Content Information

This event causes the client to send a Describe request (section 2.2.2.1) to the server. The most common scenarios in which an application would ask the client for information about multimedia content are the following.

  1. A media player application that intends to play multimedia content, which 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 about what audio and video streams are included in the content, what decoders will be needed to decompress the content and other information.

  2. A cache that already has a copy of the content but must retrieve information about the content from the server to determine if the cached copy is still fresh.

  3. A server or intermediate device, such as a noncaching proxy, which is asking for information on behalf of another client.

The higher layer MUST provide the URL that will be specified in all requests sent by the client.

If the Client-Initialization-Status does not equal 1, then this will be the first request that is sent by the client, and the client MUST perform the initialization of the protocol as specified in section 3.1.3.

The client MUST then establish a TCP connection to the server by using the IP address and port number obtained by parsing the URL. Next, the client MUST send the Describe request to the server, as specified in the next section, 3.1.4.2.1.