[linux-dvb] relating PTS to 'real' time

Stefan Magdalinski public at whitelabel.org
Tue Aug 23 14:56:39 CEST 2005

John Birch wrote:
> Stef,
> There is no process relating PCR /PTS to real time (assuming by real 
> time you mean GMT or UTC etc)
> PCR values wrap at an interval greater than 24 hours.
> There is rarely any relationship between the PCR value and 'wall clock 
> time'.
> The PTS relates to the PCR - that is the PTS is the presentation time 
> stamp for the content it is embedded in (video, audio or subtitles). 
> When the PCR value in the stream matches the PTS, the content should be 
> presented (i.e. the video frame should be visible, audio heard, or 
> subtitle displayed).

ok. That makes things a lot clearer.

What I'm trying to do is break the stream into small chunks, and save 
them mapped against 'wall clock time' - If the PTS and PCR don't carry a 
reliable form of 'wall clock time', should I just make sure the PC's 
clock is accurate and use that?

I don't need subsecond accuracy, or even second accuracy. +/- a minute 
is probably ok.

> Hope this helps...
> regards
> John Birch
> Senior Software Engineer,
> Screen Subtitling Systems 
> The Old Rectory, Church Lane
> Claydon, Ipswich, Suffolk
> www.screen.subtitling.com

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