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RFC 2326 Real Time Streaming Protocol April 1998Syntax:RTP-Infostream-urlparameter= "RTP-Info" ":" 1#stream-url 1*parameter= "url" "=" url= ";" "seq" "=" 1*DIGIT| ";" "rtptime" "=" 1*DIGITExample:RTP-Info: url=rtsp://foo.com/bar.avi/streamid=0;seq=45102,url=rtsp://foo.com/bar.avi/streamid=1;seq=3021112.34 ScaleA scale value of 1 indicates normal play or record at the normalforward viewing rate. If not 1, the value corresponds to the ratewith respect to normal viewing rate. For example, a ratio of 2indicates twice the normal viewing rate ("fast forward") and a ratioof 0.5 indicates half the normal viewing rate. In other words, aratio of 2 has normal play time increase at twice the wallclock rate.For every second of elapsed (wallclock) time, 2 seconds of contentwill be delivered. A negative value indicates reverse direction.Unless requested otherwise by the Speed parameter, the data rateSHOULD not be changed. Implementation of scale changes depends on theserver and media type. For video, a server may, for example, deliveronly key frames or selected key frames. For audio, it may time-scalethe audio while preserving pitch or, less desirably, deliverfragments of audio.The server should try to approximate the viewing rate, but mayrestrict the range of scale values that it supports. The responseMUST contain the actual scale value chosen by the server.If the request contains a Range parameter, the new scale value willtake effect at that time.Scale = "Scale" ":" [ "-" ] 1*DIGIT [ "." *DIGIT ]Example of playing in reverse at 3.5 times normal rate:Scale: -3.5Schulzrinne, et. al. Standards Track [Page 56]
RFC 2326 Real Time Streaming Protocol April 199812.35 SpeedThis request header fields parameter requests the server to deliverdata to the client at a particular speed, contingent on the server’sability and desire to serve the media stream at the given speed.Implementation by the server is OPTIONAL. The default is the bit rateof the stream.The parameter value is expressed as a decimal ratio, e.g., a value of2.0 indicates that data is to be delivered twice as fast as normal. Aspeed of zero is invalid. If the request contains a Range parameter,the new speed value will take effect at that time.Speed = "Speed" ":" 1*DIGIT [ "." *DIGIT ]Example:Speed: 2.5Use of this field changes the bandwidth used for data delivery. It ismeant for use in specific circumstances where preview of thepresentation at a higher or lower rate is necessary. Implementorsshould keep in mind that bandwidth for the session may be negotiatedbeforehand (by means other than RTSP), and therefore re-negotiationmay be necessary. When data is delivered over UDP, it is highlyrecommended that means such as RTCP be used to track packet lossrates.12.36 ServerSee [H14.39]12.37 SessionThis request and response header field identifies an RTSP sessionstarted by the media server in a SETUP response and concluded byTEARDOWN on the presentation URL. The session identifier is chosen bythe media server (see Section 3.4). Once a client receives a Sessionidentifier, it MUST return it for any request related to thatsession. A server does not have to set up a session identifier if ithas other means of identifying a session, such as dynamicallygenerated URLs.Session = "Session" ":" session-id [ ";" "timeout" "=" delta-seconds ]The timeout parameter is only allowed in a response header. Theserver uses it to indicate to the client how long the server isprepared to wait between RTSP commands before closing the session dueto lack of activity (see Section A). The timeout is measured inSchulzrinne, et. al. Standards Track [Page 57]
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