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

John Birch Johnb at screen.subtitling.com
Tue Aug 23 14:46:15 CEST 2005


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).

Hope this helps...

regards

John Birch
Senior Software Engineer,
Screen Subtitling Systems  
The Old Rectory, Church Lane
Claydon, Ipswich, Suffolk
IP6 OEQ
 
www.screen.subtitling.com

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-----Original Message-----
From: linux-dvb-bounces at linuxtv.org
[mailto:linux-dvb-bounces at linuxtv.org]On Behalf Of Stefan Magdalinski
Sent: 23 August 2005 13:28
To: linux-dvb at linuxtv.org
Subject: Re: [linux-dvb] relating PTS to 'real' time


Robert Schlabbach wrote:
> From: <public at whitelabel.org>
> 
>>When grabbing channels from a dvb-t transport stream and demuxing, the
>>presentation timestamps seem to be offset from physical time. E.g. for
>>BBC One on freeview in the UK, it seems to be about 4.5 hours.
> 
> 
> MPEG-2 PTS/DTS do _not_ refer to any real time clock, but rather to the
> clock provided through the PCR.
> 

That's what I figured. If I were to rephrase my question, what is the
process for matching timestamp data from the streams to real time?

> 
>>How does this work? I've googled all over the place, but can't find an
>>explanation.
> 
> 
> You need to read ISO/IEC 13818-1 or ITU-T H.222.0. The latter can be
> downloaded for free if you register for three free standards downloads
(per
> year) at www.itu.org.

I have read it, but not found it hugely edifiying. I'm not being lazy,
just thick.

stef

> 
> Regards,
> --
> Robert Schlabbach
> e-mail: robert_s at gmx.net
> Berlin, Germany
> 
> 
> _______________________________________________
> linux-dvb mailing list
> linux-dvb at linuxtv.org
> http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb


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