If Firefox is sending an offer with payload type 120, Chrome must use payload type 120 for packets it transmits. There's no wiggle room here. And, as far as I know, Chrome does not have any bugs where it would ignore the payload types in the offer. Additionally, the answer we're getting for Chrome does not look like Chrome 121's SDP (eg; the source-level msid attributes, the lack of a source-level cname attribute, a=rtcp:1 instead of a=rtcp:9, etc). There's some sort of middlebox shenanigans going on here. I would need to see the offer/answer exchange from Chrome's perspective
Bug 1877675 Comment 19 Edit History
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If Firefox is sending an offer with payload type 120, Chrome must use payload type 120 for packets it transmits. There's no wiggle room here. And, as far as I know, Chrome does not have any bugs where it would ignore the payload types in the offer. Additionally, the answer we're getting for Chrome does not look like Chrome 121's SDP (eg; the source-level msid attributes, the lack of a source-level cname attribute, a=rtcp:1 instead of a=rtcp:9, etc). There's some sort of middlebox shenanigans going on here. I would need to see the offer/answer exchange from Chrome's perspective.