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RTCRtpCapabilities.fecMechanisms appears redundant #655

taylor-b opened this Issue Feb 4, 2017 · 3 comments


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taylor-b commented Feb 4, 2017

"red", "ulpfec" and "flexfec" already appear in the capabilities as codecs, so fecMechanisms doesn't seem to be providing any additional information.

Or, was the intention to allow for additional error correction mechanisms to be added in the future that don't appear as codecs?


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aboba commented Feb 5, 2017

@taylor-b RTCRtpCapabilities.codecs[] includes entries for "red", "ulpfec" and "flexfec". However, this info by itself does not appear to be sufficient for the shim. For example, if "red" and "ulpfec" are advertised, what does this imply about the supported combinations? For example, can "ulpfec" be used by itself, or is it only supported along with RED? So that is why fecMechanisms includes "red+ulpfec" as a mechanism. If the only entries in fecMechanisms were "red", "ulpfec" and "flexfec" then I agree it would be redundant.

@robin-raymond Can you comment on how ORTC lib deals with fecMechanisms?


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taylor-b commented Feb 6, 2017

@aboba Ah, I see. Chrome's implementation will only use ulpfec with RED, I believe; what does Edge do? We could simply mandate that implementations advertising support for RED and ulpfec support the combination.

But, given your explanation, I'm fine with things as-is. I just didn't realize what the intent was.

aboba added a commit that referenced this issue Feb 17, 2017

@aboba aboba added the PR exists label Feb 17, 2017

@aboba aboba closed this Mar 15, 2017


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ibc commented Mar 16, 2017

BTW can "ulpfec" work without RED?

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