[MMUSIC] RTSP: Open Ranges

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Hi,

This is to discuss the following issues submitted by Christian Haas:
https://sourceforge.net/support/tracker.php?aid=2038471

> Ranges may have an open start time (e.g.: "npt=-40") that refer to the
> current play/pause position to be used as start.
> (A sidenote: The ABNFs of the ranges don't have the first time optional)
> 
> Ranges may also be open ended (e.g.: "npt=0-") requesting to play until the
> end, whenever that is.
> 
> As a result, a 'fully' open range could be valid as well (e.g.: "npt=-"),
> meaning "Play from wherever the position is now until the end of the
> presentation, whenever that is".
> Thinking further, would then there be a difference between "npt=-" and
> "npt=now-"? As a result, the "now" constant could be dropped.

First, the current ABNF says the following:


  ranges-spec          =  npt-range / utc-range / smpte-range
                       /  range-ext
   smpte-range        =  smpte-type "=" smpte-range-spec
                         ; See section 3.4
   smpte-range-spec   =  ( smpte-time "-" [ smpte-time ] )
                      /  ( "-" smpte-time )

   npt-range        =  "npt=" npt-range-spec
   npt-range-spec   =  ( npt-time "-" [ npt-time ] ) / ( "-" npt-time )

   utc-range        =  "clock=" utc-range-spec
   utc-range-spec   =  ( utc-time "-" [ utc-time ] ) / ( "-" utc-time )

Which allows either: either value-, value-value or -value. It does not
allow just -.

I would also like to point out that there is a difference between now
and no value. No value reference the current pause-point. While now is
the currently ongoing time. In a time-progressing session with recording
(retention for some or full time) the pause point may be 2 min into the
session while now could be 1 hour into the session.

So in my mind - would mean from pause point until end. But that is
equivalent to no Range header. So we already have that functionality.

I would propose no change as a resolution.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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Multimedia Technologies, Ericsson Research EAB/TVM
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