[Live-devel] OnDemandServerMediaSubsession and FramedSource subclassing

[Wiser, Tyson]

Ross,

Thanks for the help.  After doing a quick test it appears that making the suggested modifications to my subclass of "OnDemandServerMediaSubsession" does work as expected.  I appreciate your great work on this library.

Tyson

-----Original Message-----
From: live-devel-bounces at ns.live555.com [mailto:live-devel-bounces at ns.live555.com] On Behalf Of Ross Finlayson
Sent: Friday, December 10, 2010 3:10 AM
To: LIVE555 Streaming Media - development & use
Subject: Re: [Live-devel] OnDemandServerMediaSubsession and FramedSource subclassing

>Basically, I need a server that streams data on demand from a live 
>source to a client.  The stream needs to be able to be sent using 
>either unicast or multicast to an address and port combination 
>dictated by the client in the SETUP message.

It's usually the server, not the client, that decides whether or not 
the stream is unicast or multicast.  The usual way for a server to 
support both kinds of stream is to have both a 
"OnDemandServerMediaSubsession" and a "PassiveServerMediaSubsession" 
- with different names, of course.  The client could use the stream 
name to choose between unicast and multicast.

In principle this would work, but in your case you'd have a problem: 
The 'reuseFirstSource' mechanism has been implemented only for 
"OnDemandServerMediaSubsession"s; not for 
"PassiveServerMediaSubsession".  Furthernore, there's no way for 
those two separate classes to share the same input source.  So, to 
have both the unicast and multicast streams reading from the same 
source, you'd need to modify the code.

A simpler alternative is to do what you seem to be doing: Allow the 
client to specify the destination address (i.e., unicast or 
multicast), using a "destination=" parameter in the RTSP "SETUP" 
message.  To support this, you'll need to define
	RTSP_ALLOW_CLIENT_DESTINATION_SETTING
before you compile "RTSPServer.cpp"; I presume that you've done this.


>First, if I wanted to subclass OnDemandServerMediaSubsession to 
>handle multicast as well as unicast, is it sufficient to change 
>getStreamParameters() so that it doesn't automatically set 
>isMulticast to False, but instead sets it based on the destination 
>address?

I haven't tested this, but yes, I believe so.  It should be easy: 
Your subclass could redefine the "getStreamParameters()" virtual 
function to do this:

void mySubclass::getStreamParameters( ...parameters... ) {
	OnDemandServerMediaSubsession::getStreamParameters( ...parameters... );
	if (IsMulticastAddress(destinationAddress) isMulticast = True;
}


>The problem, when using OnDemandServerMediaSubsession, is that I 
>don't know how to get a reference to my source object.  That object, 
>as the name of the class implies, is created on demand and I have 
>not found any functions that return to me a FramedSource* or a 
>RTPSink*.  I have made sure that I set reuseFirstSource to True when 
>creating the OnDemandServerMediaSubsession subclass, which I 
>understand to mean that there will only ever be one source.  Is 
>there a way to get a reference to that source?

Yes, when your "OnDemandServerMediaSubsession " subclass creates a 
source object - in your implementation of the 
"createNewStreamSource()" virtual function - you can store a pointer 
to the source object (e.g., in a global variable).  (Because 
"reuseFirstSource" is true, "createNewStreamSource()" should be 
called just once, so there will be only one such source object.)
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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