Subject: Re: Some questions about RTSP

From: Anup Rao <[email-masked]>
Date: Wed, 07 Jul 1999 18:31:39 -0700

Chan Gyun Jeong wrote:
> 
> Hello, all.
> 
> I am Chan Gyun Jeong who is a master student majoring in
> Computer Engineering, Kyung Hee University, Seoul, South Korea.
> 
> Nowadays, I am interested in Real-time Transport Protocol(RTP)
> and Real-Time Streaming Protocol(RTSP).
> I also have been developing a VOD system using RTP and
> RTSP.

First things first, this question is best addressed to the list :
[email-masked].

> I have some problems that I can't understand. That is how  VOD server
> could notify to clients when the media file reaches end of the file?
> 
> I think that this notification makes the client change  playing state, so the
> client can report the playing state to the end user like Real Player. I really
> need this functions.

The way to do this is to have the client issue a DESCRIBE request first, to get
a (SDP) description of the clip. The SDP description has a range parameter - see
Section C.1.5. This parameter specifies the total length of the clip.

The client should keep an mapping between RTP timestamps and NPT(normal play
time). (Appendix B explains all this). 
 So, when a received RTP timestamp maps to a NPT value >=  whats asked for(or >
than the total NPT range of the clip), the end has been reached.

In case the presentation is a "live" one, SDP can specify the range in absolute
time, so the client knows when the feed is over.

Finally, in the case where it is not known beforehand how long the feed is - a
RTCP BYE seems a reasonable way of doing it. Relying on the RTSP control channel
may not always work, since it may be long gone.

-Anup Rao.