[Live-devel] Re: [vlc-devel] RTSP trickplay support

[Dermot McGahon]

On Mon, 20 Dec 2004 11:57:14 -0800, Ross Finlayson <finlayson at live.com>  
wrote:

> It assumes, however, that all raw UDP streams are MPEG Transport  
> Streams.  Is this likely to be the case in practice?

I haven't yet seen a raw UDP stream that wasn't a MPEG-2 Transport Stream.

Granted, that doesn't mean that they don't exist, but it seems that raw UDP
is used by set-top box and video-on-demand manufacturers and in those
environments they always use MPEG-2 Transport Stream. It's an industry
standard, the content from Hollywood comes in MPEG-2 TS and that is what
they stream over what ipTV networks that exist.

There are MPEG-4 set-top boxes starting to make an appearance. As in there
are products, but not many actually installed. Some VOD servers also have
MPEG-4 capability. But, I haven't seen any that use raw UDP MPEG-4, they
seem to have learnt from the past and are all implementing MPEG-4/RTP.

So, I can't say that it's a definitive answer but I know for sure that the
only raw UDP that a Kasenna server will create is MPEG-2 TS. I've sent an
email to BitBand asking them to confirm the same, it's not obvious from the
docs that I have.


> If not, is there something in the SDP description that will indicate 
> this?  (Does the SDP description for such streams still contain anything 
> useful in the RTP payload format code field (on the "m=" line)?)

In the case of the Kasenna, there is. In RTSPClient we have both  
fServerIsKasenna
and fKasennaContentType. Either would be good enough as a guard around this
statement. At the moment, when translating from x-rtsp-mh to SDP, we don't  
pass
the fKasennaContentType in the SDP but that should be possible.

I just tried a quick if (fServerIsKasenna) guard around this statement, but
it is a member variable of RTSPClient and I'm not sure that MediaSession is
supposed to be reading variables from this object.

Could I ask the question another way - There was support for raw UDP  
streams in
the codebase before I came along. Why was it introduced?



Dermot.
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