We are trying to enable FEC on audiobridge with AudioBridge-generated offers and I can’t find any way (except just changing sdp on client) to set useinbandfec=1.
I already set expected_loss = 20, default_expected_loss = 20, codec = “opus” (which is default afaik, but just in case), but the offer from audiobridge is still “a=fmtp:111 0 maxplaybackrate=48000; stereo=0; sprop-stereo=0; useinbandfec=0”
Am I missing something?
The offer is irrelevant, since the AudioBridge doesn’t consume FEC but only originates it. As long as your answer contains the useinbandfec=1 attribute, it should work.
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Re-reading RFC 7587, though, although those Opus SDP properties are declarative and unidirectional, it also says
The “useinbandfec” parameter is a unidirectional receive-only parameter
which means we should maybe set it to 1 if the browser only enables it if we enable it. The code currently only enables FEC if it’s set to 1 in the offer we get from the user, which if I understand the RFC text correctly actually means the user supports receiving FEC rather than sending it.
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Thanks for a quick and very detailed answer!