Subject: RE: [AVT] one question about the MPEG-4 generic RTP payload format(multiSL)

From: [email-masked]
Date: Mon, 4 Feb 2002 17:13:19 +0100

OK,
I propose to change:

"  According to RFC1889 [5, Section 5.1] timestamps are recommended to 
   start at a random value for security reasons. However then, a 
   receiver is not in the general case able to reconstruct the original 
   MPEG-4 Time Stamps (CTS, DTS, OCR) which can be of use for 
   applications where streams from multiple sources are to be 
   synchronized (for example one stream from local storage, another 
   from a streaming server). Therefore the usage of such a random 
   offset SHOULD be avoided. "

into

" Since, according to RFC1889 [5, Section 5.1], timestamps are recommended 
to 
   start at a random value, a  receiver is not in the general case able to 
reconstruct the original 
   MPEG-4 Time Stamps (CTS, DTS, OCR) which can be of use for 
   applications where streams from multiple sources are to be 
   synchronized (for example one stream from local storage, another 
   from a streaming server). Therefore such applications require
the transport out of band of the random offset, which is not in the scope
of this specification."

Regards,

Philippe Gentric
Software Architect
Philips MP4Net
[email-masked]
http://www.mpeg-4.philips.com

Dave Singer <[email-masked]>
02/01/2002 00:49

        To:     Philippe Gentric/LIM/CE/PHILIPS@EMEA1
Franceschini Guido <[email-masked]>
        cc:     [email-masked]
[email-masked]
        Subject:        RE: [AVT] one question about the MPEG-4 generic RTP payload 
format(multiSL)
        Classification: 

I'm with Philippe

the packaging spec that allows both RTP and other delivery means 
should specify how the time-lines are aligned.  Only one solution is 
using the same bit-values;  the kind of RTP-NTP mapping that RTSP 
does is another.  Yet a third is simply knowing that the two pieces 
of content have a simultaneous start, and driving them from the same 
clock.  There are many.  Such a spec should also discuss how to 
manage buffers when the two sources are not synchronized (basically, 
you have to run at the speed of the slowest source and buffer the 
faster ones).  It's a bigger question than a mere "should not" in 
this spec.
-- 
David Singer
Apple Computer/QuickTime