[Live-devel] NAL units sharing presentation time

[Mike McNamara]

All,

I'm working on a project where I need to consume H.264 data streamed from a webcam via RTSP.  This is remarkably easy with Live555!  Many thanks to Ross and everyone else.  I'm currently confused by a particular sequence of NAL units that I see in the stream over and over and was hoping that someone more knowledgeable than myself might have some insight for me.  Here's some output from a DummySink:

video/H264:	Received 10547 bytes.	Presentation time: 1379699108.138589!
audio/PCMU:	Received 1024 bytes.	Presentation time: 1379699108.189569!
video/H264:	Received 10962 bytes.	Presentation time: 1379699108.178622!
video/H264:	Received 8651 bytes.	Presentation time: 1379699108.218655!
video/H264:	Received 10621 bytes.	Presentation time: 1379699108.258688!
video/H264:	Received 45 bytes.	    Presentation time: 1379699108.258688!
video/H264:	Received 4 bytes.	    Presentation time: 1379699108.258688!
video/H264:	Received 79400 bytes.	Presentation time: 1379699108.298721!
audio/PCMU:	Received 1024 bytes.	Presentation time: 1379699108.317569!

...

video/H264:	Received 10486 bytes.	Presentation time: 1379699109.139414!
audio/PCMU:	Received 1024 bytes.	Presentation time: 1379699109.213569!
video/H264:	Received 11426 bytes.	Presentation time: 1379699109.179447!
video/H264:	Received 8681 bytes.	Presentation time: 1379699109.219480!
video/H264:	Received 10878 bytes.	Presentation time: 1379699109.259513!
video/H264:	Received 45 bytes.	    Presentation time: 1379699109.259513!
video/H264:	Received 4 bytes.	    Presentation time: 1379699109.259513!
video/H264:	Received 82291 bytes.	Presentation time: 1379699109.299546!
audio/PCMU:	Received 1024 bytes.	Presentation time: 1379699109.341569!

etc....

What are the 45 and 4 byte NAL units that share the same presentation time as the preceding H.264 NAL unit?  

The payload of these 45 and 4 byte units is identical in every case:

<674d0029 9a6280f0 044fcb35 01010140 0000fa40 003a983a 1800bb80 002ee06e f2e34300 17700005 dc0dde5c 28>

and:

<68ee3c80>

respectively.  Neither appears to be a start code or delimiter?  I'm definitely outside of my sphere of knowledge, so any advice would be appreciated.

Thanks!


Mike

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