[Live-devel] Live555 presentation times jump when joining multicast streams

[DJM-Avalesta]

> So, I suggest adding, to your server code, code that compares the value 
> of 'fPresentationTime" computed your new way,

> with the value that would be computed by calling "gettimeofday()", and 
> print out the difference

Thanks, Ross. I assume you mean, if the new presentation time becomes 
different from wall clock time by a large amount, eg more than 1 second, 
I should reallign fPresentationTime with wall clock time, like this

     if (fPresentationTime.tv_sec == 0 && fPresentationTime.tv_usec == 0)
     {
         gettimeofday(&fPresentationTime, NULL);
         INFO("setPresentationTime: %ld.%06ld\n", 
fPresentationTime.tv_sec, fPresentationTime.tv_usec);
     }
     else
     {
        // Increment by the sample time
         unsigned uSeconds = fPresentationTime.tv_usec + 
(unsigned)(1000000.0/fMaxFps);
         fPresentationTime.tv_sec += uSeconds/1000000;
         fPresentationTime.tv_usec = uSeconds%1000000;

         //check for basic alignment with 'wall clock' time
         struct timeval wallclocktime;
         gettimeofday(&wallclocktime, NULL);
         if ((wallclocktime.tv_sec > fPresentationTime.tv_sec + 1) ||
                 (fPresentationTime.tv_sec > wallclocktime.tv_sec + 1) )
         {    //we have drifted too far from wall clock time so need to 
realign
             fPresentationTime.tv_sec = wallclocktime.tv_sec;
             fPresentationTime.tv_usec = wallclocktime.tv_usec;
             INFO("Realigning PresentationTime with wall-clock time: 
%ld.%06ld\n", fPresentationTime.tv_sec, fPresentationTime.tv_usec);
         }
     }
This seems to work but will need more testing. VLC seems to be very 
sensitive to presentation time jumps or anomalies.
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