The line is really blurry between what is right and what works better. I think the only real rule about the marker bit is that you are supposed to set it any time the timestamp is not the next expected timestamp. This is supposed to help you to understand that you are purposely sending a packet that has a different timestamp base or that you are resuming after intentionally not sending packets for a period of time. This tells the remote end to flush its jitter buffer which probably explains the drop in audio. If changing the SSRC is an acceptable workaround for when the rtp streams change that do not result in audio gaps, I'm more than happy to accept it as a default and we can always make it a config option if it presents any problems. On Tue, Jul 3, 2012 at 9:39 AM, Peter Olsson <peter.olsson@visionutveckling.se> wrote:
When I’ve been debugging RTP streams in Wireshark, I’ve noticed that Whireshark will get “everything wrong” when the timestamp changes (is reset). For instance, if I call a conference, by the time I get into the conference, the RTP timestamps will start over, and FS will send the marker bit By that time Wireshark will report strange figures for jitter etc.
After some Googling I’ve found that the meaning of the RTP marker is to indicate “the beginning of a talkspurt”. Which is not very clear to me... :)
So my question is – is RTP marker really enough when starting a “new RTP stream” (not really new, but since the timestamps are reset we can think of it like that) – according to what I’ve been able to find, maybe the SSRC should also be changed?
I have created a patch that will change the SSRC when a reset like this occurs, and after that Wireshark detects my audio streams without problems (though, it will detect more streams), but no strange jitter figures etc. are reported.
The reason I started digging into this was because a PBX I was connecting to lost about the first second of audio after connecting to the conference, after also changing the SSRC the problem seems resolved.
I could make a RTP_BUG setting for this, but I’m not really sure if I should really care – that’s why I’m asking here, if anyone has more knowledge about this?
/Peter
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