Minutes IETF119: mlcodec: Wed 05:00
minutes-119-mlcodec-202403200500-00

Machine Learning for Audio Coding (mlcodec) Working Group

MLCODEC @ IETF 119 in Brisbane, Australia

15:00-16:30 AEST Wednesday, March 20, 2024 in room M1
22:00-23:30 PDT Tuesday, March 19, 2024

Chairs: Greg Maxwell, Mo Zanaty
Area Director: Murray Kucherawy
Note Taker: Victor Pascual

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Agenda

1. Administrivia - Chairs, 5 min
   Note well, agenda bash, draft status

2. Opus extension mechanism - Timothy Terriberry, 15 min
   draft-ietf-mlcodec-opus-extension

Conversation so far has focused on developing an extension numbering
scheme for the Opus audio codec draft. The main topics discussed
include:

• Proposing a system that splits extensions into short and long
  categories, with different numbering approaches for each.

• Debating the priorities and use cases of potential future extensions
  to help inform the design, like enhancements that may send side
  information.

• Considering proposals to more efficiently allocate the extension
  identifier space to reduce overhead for things like variable length
  extensions.

• Discussing current Opus packet sizes and how short extensions could
  benefit certain types of data payloads.

• The need for more review of the draft and further development of
  enhancement proposals before finalizing the numbering scheme.

1. Deep REDundancy - Jean-Marc Valin, 25 min
   draft-valin-opus-dred

• Changes made to Dred since the last meeting, including adding an
  optional extended offset byte to allow encoding backwards in time
  and more efficiently trimming silence.

• Questions around how the dread extensions impact audio level
  calculations and speaker switching decisions by SFU systems.

• Clarification provided that the encoder will not encode dread for
  periods of silence.

• Discussion of publishing the normalization aspects of Dred, such as
  defining acoustic features for speech recognition in a standardized
  way.

• Details provided on the implementation status of Dred and available
  WebRTC patches for testing.

• Results reported from WebRTC experiments showing quality
  improvements with extended offsets handling packet loss situations.

• Open parameters like maximum dread duration and lowest/highest
  supported bitrates.

• Open questions raised on potential truncation support and solutions
  for publishing binary data.

• Comments on the timing for an adoption call for the draft and any
  remaining changes needed.

  Adoption vote:10 yes, 2 no opinions, 20 in the room.

1. Speech coding enhancements - Jan Buethe, 25 min
   draft-buethe-opus-speech-coding-enhancement

• Clarification was provided that the hybrid mode in Dred is
  compatible across channels and improves quality in stereo and group
  stereo use cases.

• A question was asked about how the hybrid mode physically separates
  the processed and unprocessed components.

• Next steps discussed for algorithm development include supporting
  higher bandwidths and more frames of redundancy.

• Standardization next steps proposed taking the full implementation
  into account and defining quality requirements.

• Signaling of enhancement techniques was discussed, as well as
  potential naming schemes to identify versions.

• A point was made that the proposed flag to disable enhancements for
  non-speech content is not technique-specific.

• Clarification was provided that the single-speaker training of
  current speech models has also been tested on real recordings.

• The conversation wrapped up by confirming there were no other topics
  or questions to discuss.