3.1.4.2 Request to Retrieve Content Information

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

  • 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, for example, retrieve information on what audio and video streams are included in the content and what decoders will be needed to decompress the content.

  • 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 non-caching proxy, that 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 InitialRequest, the client MUST perform the initialization of the protocol, as specified in section 3.1.3, and set the InitialRequest value to 1.

The client MUST then establish a TCP connection to the server, 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 section 3.1.4.2.1.