RTCP packets with odd up ssrcs and timestamps

[ebu...@thrupoint.com]

Testing with Chrome 25.0.1364.172 for linux I'm seeing RTCP packets with the SSRC incrementing with each packet (starting with 2147483649) and the timestamps staying the same.

The ssrc seems to be the closest to the timestamp for the rtp packets (2091489463 - 2091518903), but none of the numbers (ssrcs or timestamps) are anywhere close to any ssrcs given in the SDP. I'm also used to seeing the sequence number for rtcp being 6, but it's 1 for all the these packets.

I'm muxing the rtcp and whilst video goes out in the original offer as it can be received, neither side has a webcam. So I'm wondering if anyone else has seen this, or a clue as to what I might be doing wrong, or if it is a bug that I need to raise.

Thanks

Eric

[kapejod]

Hi,

most likely you are decoding RTP data as RTCP. This will "map" the sequence number header field (from RTP) into the ssrc header field of RTCP.

This is the sort of fun you get when multiplexing RTP and RTCP (and STUN.... and DTLS...) on the same port. :-)

best regards,

Klaus 

[ebu...@thrupoint.com]

And here I was hoping this was the cause behind the lack of audio I am having, and a separate "Failed to unprotect audio RTP packet" error. Back to searching for any faults in my code.

Thanks.

[kapejod]

Before you call srtp_unprotect_rtp or srtp_unprotect_rtcp make sure that the ssrc matches your expectation

by looking at the ssrc through a srtp_hdr_t and srtcp_hdr_t structure.

Cheers,

Klaus

[ebu...@thrupoint.com]

I'm getting Chrome throw out the unprotect errors, so it's not me using the libraries directly.

Decoding the RTCP packets correctly in wireshark, I am still seeing an ssrc that hasn't been included in the SDP though, which is causing a problem for my packet routing server. It does seem to only be when I don't have a webcam plugged in though, though with a webcam I am seeing occasional lack of video and sound after the initial key frame. It works with apprtc though, so I can only presume I am doing something wrong.

Thanks.

Eric