On 1/27/2016 1:53 PM, Christian wrote:
Hi,
We are trying to analyze a problem with a RTCPeerConnection between
Firefox 44.0 and a Cisco 8520 MCU (connected via the Janus WebRTC
Gateway (https://github.com/meetecho/janus-gateway)). Unfortunately,
we've got stuck. :(
Problem description: The remote SDP gets accepted by Firefox, but no
video is playing.
local SDP:
[...]
a=fmtp:126
profile-level-id=42e01f;level-asymmetry-allowed=1;packetization-mode=1
a=fmtp:97 profile-level-id=42e01f;level-asymmetry-allowed=1
[...]
remote SDP:
[...]
a=fmtp:97
profile-level-id=420016;level-asymmetry-allowed=0;max-mbps=108000;max-fs=3840;max-dpb=5408
a=fmtp:126
profile-level-id=420016;level-asymmetry-allowed=0;packetization-mode=1;max-mbps=108000;max-fs=3840;max-dpb=5408
[...]
RFC 6184 8.2.2:
o The parameters identifying a media format configuration for H.264
are profile-level-id and packetization-mode. These media format
configuration parameters (except for the level part of profile-
level-id) MUST be used symmetrically; that is, the answerer MUST
either maintain all configuration parameters or remove the media
format (payload type) completely if one or more of the parameter
values are not supported. Note that the level part of profile-
level-id includes level_idc, and, for indication of Level 1b when
profile_idc is equal to 66, 77, or 88, bit 4
(constraint_set3_flag) of profile-iop. The level part of profile-
level-id is changeable.
i.e. you can't answer profile-level-id=42e0xx with 4200xx - they don't
match. Many H264 impls ignore the constraint bits and hope things
just work. As it's invalid, we should probably call the error
callback, but I think instead it just didn't start send or receive for
video.
Also: I would generally suggest using Mode 1 and not mode 0. While it
may not matter (most implementations that support both handle this)
but mode 0 has a bug where we send SPS/PPS in a STAP-A packet (which
is mode-1 only).
Randell Jesup
Thank you very much for your explanation!
I have contacted the owner of the MCU and asked for filing a bug report
at Cisco. I hope that they'll fix this soon -- the device is expensive
enough....
Christian
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