What does HRESULT 0x80EE0000 (RTC_E_SIP_CODECS_DO_NOT_MATCH) mean?

RTC_E_SIP_CODECS_DO_NOT_MATCH

What the RTC value marks: RTC_E_SIP_CODECS_DO_NOT_MATCH

This result is useful only when preserved with its producing phase; in parsing, constructing, or reconciling SIP signaling and the SDP offer/answer carried by it, it denotes the local offer and remote answer have no common codec for an active media line.

The machine-readable identity of this result is 0x80EE0000 in the RTC interface facility 0xEE; the result identity matters because RTC uses separate facilities for API conditions, SIP final responses, and PINT service statuses.

The first useful check is to compare payload types and rtpmap/fmtp values per m= section rather than comparing codec names globally. The result must be separated from nearby conditions because a codec mismatch is media negotiation failure; it does not mean SIP transport or the audio device failed.

Protocol and object state

SIP transaction state and media negotiation are separate: a syntactically valid SIP request can still contain absent or unacceptable SDP. An SDP update must be checked against the previous offer/answer state, not merely parsed as a standalone text document.

Evidence that separates the cause

• Code-specific proof: compare payload types and rtpmap/fmtp values per m= section rather than comparing codec names globally.
• Identity and target: message direction and transport.
• State at production: start-line plus header names.
• Timing and ordering: Content-Type and Content-Length.

A safe diagnostic sequence

1. Record it and 0x80EE0000 at the first RTC method or event that returns it.
2. Apply one controlled change: offer at least one mutually supported codec with compatible parameters or select a media mode both endpoints implement; then verify the result return value and resulting RTC state.

How to handle the result

To correct this, offer at least one mutually supported codec with compatible parameters or select a media mode both endpoints implement.

Example: One endpoint offers only a proprietary audio codec while the peer accepts only PCMU; signaling succeeds but the media offer cannot be completed.

Actions that do not address this condition

• Do not repair malformed signaling by silently deleting unknown headers or media sections.
• Do not log credentials or an unredacted SDP body from production calls.

Related RTC results

Technical references

• Microsoft RTC return constants.
• SIP message and transaction rules.
• SDP syntax.
• SDP offer/answer.