[vlc-devel] New support in the LIVE555 library for computing "Normal Play Time"

Ross Finlayson finlayson at live555.com
Sat Jan 19 01:30:11 CET 2008

FYI, the latest release (2008.01.19) of the "LIVE555 Streaming Media" 
code adds support for calculating a stream's "Normal Play Time" (NPT) 
(as defined in RFC 2326, section 3.6.) from a given presentation time.

Note, in particular, the definition of
in "liveMedia/include/MediaSession.hh".

This function correctly computes the stream's current NPT either 
directly from the presentation time (if it has been synchronized 
using RTCP), otherwise using the information parsed from the stream's 
"RTP-Info:" header, along with the current RTP timestamp.  It also 
takes account of any 'seeking' that was done on the stream, and any 
'trick play' scale factor that is in effect.  (For example, if the 
stream is playing with 'scale' 2.0, then NPT will advance at 2x the 
rate of wall-clock time, while presentation time remains at the rate 
of wall-clock time.)

LIVE555 RTSP clients - such as VLC - will likely find this function 
useful when updating their GUI to show the current status of the 

Ross Finlayson
Live Networks, Inc.

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