Hello,
My name is Jennifer Valle and I am doing the final degree project in UPC
with some of its cameras, in particular, NC353L Elphel cameras with the
original code of Live555 about the RTSP protocol. I want to syncronized
different cameras and I need its timestamps.
In this code, there are a testProgs_rtsp function with a struct timeval
called PresentationTime and I think that it's the same that timestamp of
the server (cameras) when the RTCP is synchronized.
I have a problem because when I execute the program, and RTCP is
syncronized, I obtain negatives times and i don't understand why this
occurs.
The part of the code that I want to modify is in
DummySink::afterGettingFrame function.
void DummySink::afterGettingFrame(unsigned frameSize, unsigned
> numTruncatedBytes,struct timeval presentationTime, unsigned
> /*durationInMicroseconds*/) {
> // We've just received a frame of data. (Optionally) print out
> information about it:
> #ifdef DEBUG_PRINT_EACH_RECEIVED_FRAME
> if (fStreamId != NULL) envir() << "Stream \"" << fStreamId << "\"; ";
> envir() << fSubsession.mediumName() << "/" << fSubsession.codecName() <<
> ":\tReceived " << frameSize << " bytes";
> if (numTruncatedBytes > 0) envir() << " (with " << numTruncatedBytes <<
> " bytes truncated)";
> char uSecsStr[6+1]; // used to output the 'microseconds' part of the
> presentation time
> sprintf(uSecsStr, "%06u", (unsigned)presentationTime.tv_usec);
> envir() << ".\tPresentation time: " << (int)presentationTime.tv_sec <<
> "." << uSecsStr;
> if (fSubsession.rtpSource() != NULL &&
> !fSubsession.rtpSource()->hasBeenSynchronizedUsingRTCP()) {
> envir() << "(not RTCP-synchronized!)"; // mark the debugging output to
> indicate that this presentation time is not RTCP-synchronized
> }
> #ifdef DEBUG_PRINT_NPT
> envir() << "\tNPT: " << fSubsession.getNormalPlayTime(presentationTime);
> #endif
> envir() << "\n";
#endif
And I obtain "incorrects" PresentationTimes:
Stream "rtsp://pa1"; video/JPEG: Received 97775 bytes. Presentation time:
> 1448129165.229872(not RTCP-synchronized!) NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98174 bytes. Presentation time:
> 1448129165.265949(not RTCP-synchronized!) NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98264 bytes. Presentation time:
> -760859674.598727 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98233 bytes. Presentation time:
> -760859674.634804 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98228 bytes. Presentation time:
> -760859674.670881 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98644 bytes. Presentation time:
> -760859674.706947 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98337 bytes. Presentation time:
> -760859674.743024 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 98147 bytes. Presentation time:
> -760859674.779101 NPT: 0.000000
> Stream "rtsp://pa1"; video/JPEG: Received 97848 bytes. Presentation time:
> -760859674.815178 NPT: 0.000000
How could you get the correct timestamp the server gives each frame? Is it
the PresentationTime after RTCP is syncronized or is an another variable?
If I have to use the PresentationTime, why do I get incorrect values?
Kind regards.
Jennifer Valle
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