[Live-devel] getNextFrame Variables

[chenjun]

hi Zkunhui，
   Thanks for your works and your reply for my questions.I want to get the file you said about NAL units.
   Again, I want to ask a question which i refered in previous question: If the size of NAL unit is bigger than fMaxsize(should I set fMaxsize myself?),
   then   fFrameSize=fMaxsize,fNumTruncatedBytes = fFrameSize - fMaxSize  ,as the code below:
 
///////////////////////////////////////////////// 
 if (fFrameSize > fMaxSize) {   fNumTruncatedBytes = fFrameSize - fMaxSize;   fFrameSize = fMaxSize;  }
 
 memcpy(fTo,Encode_data,fFrameSize);     //Encode_data is defined in another thread
//////////////////////////////////////////////////
 
but how to deal with the fNumTruncatedBytes data?
 
in H264VideoRTPSink.cpp , i see the clue below, should i do it like this in deliverFrame()?
 
// We have NAL unit data in the buffer.  There are three cases to consider:    // 1. There is a new NAL unit in the buffer, and it's small enough to deliver    //    to the RTP sink (as is).    // 2. There is a new NAL unit in the buffer, but it's too large to deliver to    //    the RTP sink in its entirety.  Deliver the first fragment of this data,    //    as a FU-A packet, with one extra preceding header byte.    // 3. There is a NAL unit in the buffer, and we've already delivered some    //    fragment(s) of this.  Deliver the next fragment of this data,    //    as a FU-A packet, with two extra preceding header bytes.
 
 
Thanks in advance. I am looking forward helps from anyone!


Date: Sat, 6 Jan 2007 07:06:36 +0800From: TAYK0004 at ntu.edu.sgTo: live-devel at ns.live555.comSubject: [Live-devel] getNextFrame Variables


Hi guys,
 
once again, great thanks to Ross for helping me clear many doubts in RTP.
 
I have some uncertainties regarding DoGetNextFrame() Variables, which I hope anyone can assist.
 
fTO : a RTP buffer, we are to copy video data into this buffer for framing
eg.  g_video_enc_rbuf->read(fTo, fMaxSize, 0); //the read function will copy the data to fTo
       memcpy(fTo,g_video_enc_rbuf,fFrameSize); // using memcpy function
 
fPresentationTime: give time information to each frame
 
eg. gettimeofday(&fPresentationTime, NULL); //a simpler form
 
// a more detailed form
if (fPresentationTime.tv_sec == 0 && fPresentationTime.tv_usec == 0) {
      // This is the first frame, so use the current time:
      gettimeofday(&fPresentationTime, NULL);
    } else {
      // Increment by the play time of the previous frame (50ms), my encoder’s frame rate is 20fps
    unsigned uSeconds         = fPresentationTime.tv_usec + 50000;
    fPresentationTime.tv_sec += uSeconds/1000000;
    fPresentationTime.tv_usec = uSeconds%1000000;
 
fMaxSize: Setting the maximum size of a rtp frame. Not necessary if you have already set your encoder to limit the size of a frame. For truncation purpose.
 
eg. Can anyone provide some examples on setting fMaxSize?
 
fFrameSize: Determine the RTP frame size
 
eg. Can anyone provide some examples on setting fFrameSize?
 
 
 
That’s all I can think of for the variables for DoGetNextFrame. If I miss out anything, pls kindly add in.
 
I compiling all the emails which contains information on these information so that anyone in future can refer to them instead of asking again in the mailing list. I can share a file which I have done detailing on NAL units so that people doing h.264 framer can have a better understanding when writing the code.
 
Many thanks and regards.
 
 
Zkunhui
 
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