[Live-devel] Local clock drift/offset compensation?

[Ross Finlayson]

>Well, but the mediaplayer does not have all the necessary information to
>correctly compute the clock drift - for example, the real packet arrival
>time is not known by the mediaplayer.

Because of network jitter, the 'real packet arrival times' are 
actually not particularly useful (and, in any case, are known only 
precisely by the OS's network drivers, not by higher-level code (such 
as the "LIVE555 Streaming Media" code)).

Typically, the way that media players deal with skew between the 
sender's and receiver's clocks is by clever use of a playout 
buffer.  If the buffer gets close to overflowing, the media player 
can slow down consumption from the buffer by duplicating audio 
samples and/or video frames, and/or by increasing the gaps between 
audio 'talk spurts'.  If the buffer gets close to overflowing, the 
media player can speed up consumption from the buffer by skipping 
audio samples or video frames, and/or decreasing the gaps between 
audio 'talk spurts'.


	Ross Finlayson
	Live Networks, Inc. (LIVE555.COM)
	<http://www.live555.com/>