You replied to Sean:
If you're streaming MPEG-4 video via RTP, then you must use a RTSP server.
It is my understanding that one purpose of RTSP when streaming MPEG4
video is to communicate the all-important SDP info to the client
player. And I understand that's why Sean and I (and the whole rest
of the world) require RTSP to stream MPEG4 video.
Yes.
But you also replied to me (in
<http://lists.live555.com/pipermail/live-evel/2009-June/010842.html>):
In princlple, all RTP media players need to first receive a SDP
description that describes the stream.
So if one is streaming MPEG2 video instead of MPEG4, the SDP is
still required. But then how would one's client player even get an
SDP presuming MPEG2 means no RTSP?
Who said that "MPEG2 means no RTSP"? I certainly didn't.
It's really quite simple:
1/ If you are streaming RTP via unicast, then you should use RTSP (in
order to ensure that the client will know both the client and
server's port numbers for RTP/RTCP).
2/ If you are streaming RTP via multicast, then RTSP is optional.
However, if you don't use RTSP, then you will need to give a SDP
description to the client some other way (e.g., by having it read a
file). (Therefore, RTSP is recommended, even for multicast streams.)
Depending on your client and your codec, you might sometimes be able
to violate these rules. For example, if you are streaming MPEG-1 or
2 audio, video, or transport stream data to VLC via multicast, then
you might not need to give VLC a SDP description (because VLC can
sometimes 'guess' the codec). And if you somehow know for sure that
the server and client will use the same port numbers for RTP and RTCP
(this usually means having only one client), then you might sometimes
be able to stream via unicast without using a RTSP server. However,
if you try doing either of these, you will get no support from me.
For simplicity, everyone should just use RTSP for all RTP streams.
--
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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