Subject: [MMUSIC] RTSP 2.0: Proposed NPT range enhancement

From: Sean Sheedy <[email-masked]>
Date: Tue, 04 Dec 2007 12:04:36 -0800

Recently a customer came to me with the question: what's a good way to
achieve skip-forward semantics in RTSP? An example of this would be
jumping forward 30 seconds from the current position to skip an
advertisement.

Currently, the only way to do this is to query for the current position
and then use the returned value plus 30 seconds in a new PLAY request.
Unfortunately, the delay from the extra round trip can cause both
inaccuracy in the new play position and a degraded end-user experience.

To address this, I'd like to propose an enhancement to the NPT range
syntax.  An offset from the currently playing position could be
specified as "current+" followed by the number of seconds.  For example:

    Range: npt=current+30-

would specify from 30 seconds beyond the current position to the end of
media.  To keep things symmetric, we could skip backwards by using
"current-".  The response would always contain the actual range being
played; i.e., "current+" or "current-" would be illegal in a response.

The formal syntax of this would be:

   npt-time         =  "now" / npt-sec / npt-hhmmss / rel-time
   rel-time         =  ( "current+" / "current-" ) npt-sec

Comments?

-- 
Sean Sheedy                                         [email-masked]
(503) 531-6427

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