**Session Date/Time:** 20 Mar 2024 05:00

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# mlcodec

## Summary

The mlcodec working group met at IETF 119 in Brisbane, Australia. The agenda included updates on the OPUS extension mechanism, deep redundancy (DRED) for OPUS, and speech coding enhancements. Key discussions revolved around extension ID numbering for OPUS, the architecture of DRED including signaling and interaction with SFUs, and the approach to standardizing speech enhancement techniques. The group agreed to adopt the DRED draft as a working group item and identified action items to progress the OPUS extension mechanism draft.

## Key Discussion Points

*   **OPUS Extension Mechanism:**
    *   Discussion on the optimal extension ID numbering scheme (short vs. long extensions, allocating in pairs).
    *   Debate on whether to finalize the extension mechanism before understanding the properties of future extensions, especially those related to speech enhancements.
    *   Proposal to flatten the extension ID space and enumerate all 256 code points.
    *   Agreement to prioritize closing off on the extension ID numbering scheme to stabilize deployments.
*   **Deep Redundancy (DRED):**
    *   Update on changes to the DRED draft since the last meeting, including the addition of an extended offset field.
    *   Discussion on the SFU use case and potential guidance on how DRED interacts with audio levels used for forwarding decisions.
    *   Consideration of Qmax field for controlling the upper bound of the quality quantizer.
    *   Debate about standardization, focusing on the on-wire bits to vocoder feature transformation with DNN weights frozen and normative.
    *   Questions regarding the need for maximum duration allowed, and concerns with conferencing late joiner cases. The group agreed to change the SDP parameter to a MUST.
    *   Truncation of DRED packets - decision to postpone to the future if necessary.
*   **Speech Coding Enhancements:**
    *   Update on the integration of enhancement methods into OPUS 1.5 release.
    *   Discussion about whether there should be signaling about enhancements.
    *   Discussion of the properties of content that isnt speech.
    *   Consideration of an in-band flag for disabling enhancements.

## Decisions and Action Items

*   **Decision:** The mlcodec working group agreed to adopt the deep redundancy (DRED) draft as a working group item.
*   **Action Item:** Jean-Marc to prepare and submit the DRED draft as a working group draft, incorporating the changes discussed during the meeting. Submit after the adoption call has ended in two weeks.
*   **Action Item:** Jean-Marc to incorporate some of the discussion regarding guidance for use with SFUs into the DRED draft.
*   **Action Item:** Jean-Marc to add text to the DRED draft regarding the case where two DRED extensions are present in a single packet.
*   **Action Item:** Jean-Marc to add text that encoders SHOULD NOT encode dread of silence.
*   **Action Item:** Tim to publish the updated version of the OPUS extension mechanism draft.
*   **Action Item:** Tim and others to prioritize reviewing the OPUS extension mechanism draft, focusing on SDP negotiation and extension ID numbering issues.

## Next Steps

*   Confirm the adoption of the DRED draft on the mailing list and set a two-week adoption call.
*   Jean-Marc to submit the updated DRED draft as a working group item.
*   Continue discussions on the mlcodec mailing list regarding the OPUS extension mechanism, specifically focusing on the extension ID numbering scheme.
*   Seek more reviews and feedback on the OPUS extension mechanism draft.
*   Jan to try speech coding enhancements on content that is not speech.