Subject: [MMUSIC] RTSP: The use of the SDP attribute "a=range:"

From: Magnus Westerlund <[email-masked]>
Date: Thu, 21 Aug 2003 16:47:27 +0200

Hi,

During the 57th IETF meeting we discussed the meaning of open intervals 
for the SDP attribute a=range, e.g. "a=range:npt=0-". My memory and 
notes indicates that the conclusions made was:

1. An open range indicates a media with unknown duration.

2. There seem to be need for more attributes expressing things like: 
seekability.

The start of the discussion on this topic was the usability of an open 
range to indicate that media is live and not seekable. There where 
comments that even though a session is live it might be seekable, at 
least into the past, i.e. behind "now". This is can be accomplished by 
on the fly recording servers. However there is a lack of possibility to 
express this capability.

There are currently implementations that interpret an open range as not 
being seekable, for example the quicktime 6.3 player. So to rehash the 
question in this forum:

Would it be acceptable to define an open interval range attribute as 
being live and non seekable unless other attributes give further 
properties, like seekable?

If you own a commercial implementation of a RTSP client, could you 
please inform how it would react to an open range?

Looking forward to your comments.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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From: "Amir Wolf" <[email-masked]>
Date: Fri, 22 Aug 2003 00:23:53 +0300

Hi Magnus,
In the PSS AG we have been testing live as part of our interoperability tests.
The vendors that supplied the live feeds (servers) used an open range as an identifier for the link being a live link.
It appears that all the clients got the message and treated this session as live. 

	-----Original Message----- 
	From: Magnus Westerlund [mailto:[email-masked]] 
	Sent: ה 21/08/2003 17:47 
	To: IETF MMUSIC WG 
	Cc: 
	Subject: [MMUSIC] RTSP: The use of the SDP attribute "a=range:"

	Hi,

	

	

	
	Cheers
	
	Magnus Westerlund

	

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