[Elphel-support] Problems to detect timestamps

[support-list]

Hello Jennifer,

The original Live555 implementation is rather old - I did not know it still works, there are some newer RTSP streamers. That first streamer (written by Ross himself) was made before the FPGA was providing the exact time stamp of each image. The FPGA is providing JPEG-compressed data in the circular buffer, aligning each new frame to 32 bytes and leaving additional gaps between frames, and the extra data after each frame includes 2 of the 32-bit words - seconds and microseconds of the time when the frame acquisition was started. You may find the code that extracts the timestamp here:
http://elphel.cvs.sourceforge.net/viewvc/elphel/elphel353-8.0/apps/astreamer/video.cpp?view=markup (line 254)

What is the overall software version in the camera that you are using?

Andrey


---- On Sat, 21 Nov 2015 10:17:04 -0800 Jennifer Valle <jvs1192 at gmail.com> wrote ---- 

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

 _______________________________________________ 
Support-list mailing list 
Support-list at support.elphel.com 
http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com 




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://support.elphel.com/pipermail/support-list_support.elphel.com/attachments/20151121/a5580b06/attachment-0002.html>