2.2.7.2 Describe

The purpose of the Describe request is to request information on one particular piece of multimedia content, which is identified by a URL. The client sends this request before it asks the server to start streaming the content. The server's response describes the content using SDP syntax (section 2.2.5), providing the ASF file header as well as a URL for each stream and information on the RTP payload format for each stream. If the URL in the Describe request identifies a server-side playlist, the SDP in the Describe response describes only the first entry in the playlist.

The Describe request is implemented by using the DESCRIBE request method, and MUST adhere to the syntax for DESCRIBE, as specified in [RFC2326] section 10.2.

The Describe request also MUST include the User-Agent (section 2.2.6.12) header, and SHOULD include the Supported (section 2.2.6.10) header and the X-Accept-Authentication (section 2.2.6.14) header. The Cookie (section 2.2.6.4) header MUST be included if there are any applicable cookies to send to the server.

The response to the Describe request SHOULD specify the Cache-Control (section 2.2.6.2) header.

The message body in the response to the Describe request MUST contain the SDP in accordance with the rules specified in section 2.2.5. The SDP MUST be identified by the media type application/sdp on the Content-Type (section 2.2.6.3) header.

The following example shows a Describe request.

 DESCRIBE rtsp://myserver.com/mycontent.wmv RTSP/1.0
 User-Agent: WMPlayer/9.0.0.2833 guid/B64345F5-8C45-4818-8A1A-4775F0923FAC
 Accept: application/sdp
 Accept-Charset: UTF-8, *;q=0.1
 X-Accept-Authentication: Negotiate, NTLM, Digest
 Accept-Language: en-US, *;q=0.1
 CSeq: 1
 Supported: com.microsoft.wm.srvppair, com.microsoft.wm.sswitch, 
 com.microsoft.wm.eosmsg, com.microsoft.wm.predstrm