Subject: [rtcweb] What is wrong with probation (just padding) RTP packets within the media stream?

From: Iñaki Baz Castillo <[email-masked]>
Date: Thu, 21 Sep 2017 22:23:10 +0200

Hi, just wondering if something is "illegal" in the following approach:

- For each RTP video packet received, the server (an SFU) also sends a
probation RTP packet to the receivers.

- Such a RTP probation packet has the same media SSRC and PT, with
marker bit=0, padding bit=1, zero payload and N bytes of padding. It
also has the same RTP timestamp that the video media packet and seq+1.

However, the receiver (Chrome in this case) does not render video. By
enabling its webrtc logs it does not complain at all.

Said that, I've also tried to send those probation packets *just*
after a video packet with marker bit=1. And it works.

It seems that, having the same timestamp than an already completed
video frame, Chrome does not complain. However I wonder what is wrong
with sending the above probation packets between video packets with
same ts and marker bit=0. Why is that wrong? or is it just that this
specific browser does not like it for any reason?

Thanks a lot.

-- 
Iñaki Baz Castillo
<[email-masked]>