Markdown Version | Session Recording

Session Date/Time: 23 Jan 2024 20:00

CELLAR

Summary

The CELLAR Working Group discussed the status of its various drafts, including the Matroska container (now in the RFC Editor queue) and FLAC (discuss points cleared). Key discussions revolved around the strategy for the Matroska extension documents, particularly the codec specification, and the future direction of FFV1 Version 4, including addressing GPU acceleration needs and avoiding multiple backward compatibility breaks. Action items were assigned for milestone updates, draft regeneration, and starting work on FFV1v4.

Key Discussion Points

• Review of Previous Meeting Minutes (October Interim):

  • Minutes from the October interim meeting were approved without further comments.
  • Feedback from the "No Time to Wait" event included requests for GPU acceleration for FFV1 due to perceived slowness, and a desire for better specification of flags.
  • It was noted that the US Library of Congress and other federal agencies are considering FFV1 and Matroska as preferred formats, partly due to the ongoing standardization work within CELLAR.

• Status Update:

  • Matroska (Base Specification): Officially in the RFC Editor queue, awaiting publication.
  • FLAC: All discuss points have been cleared. A normative down-reference to RFC 2083 (ID3v2 picture types), which is an informational document, was identified. This is being reviewed by the ISG in consultation with Murray (AD), considering BCP 97 regarding down-references to lower-maturity documents.
  • Expired Drafts: Several adopted drafts, including draft-ietf-cellar-ffv1-v4, draft-ietf-cellar-matroska-codec, draft-ietf-cellar-matroska-control, draft-ietf-cellar-matroska-chapter-codecs, and draft-ietf-cellar-matroska-tags, had recently expired. ffv1-v4 has since been updated.

• Matroska Extension Documents Strategy:

  • Discussion on the timeline and leads for the adopted Matroska extension documents.
  • draft-ietf-cellar-matroska-tags: Expected to be the fastest to complete, with a target of end of year.
  • draft-ietf-cellar-matroska-codec: Identified as a significant and complex effort due to the messy nature of the original document. No clear timeline was set, and Moritz was suggested as a potential lead for this document due to his expertise.
  • The structure of the codec specification was debated: whether to have one large document covering all major codecs or separate documents per codec. The current inclination is to consolidate existing major codecs (e.g., MPEG, H.264/265, AV1, MP3, AAC, PCM, Opus, common subtitle formats like Text, SSA, WebVTT) into one document initially, potentially with separate documents for new or highly complex codecs later. This approach aims to avoid managing too many individual documents while providing a comprehensive definition for widely used codecs.
  • draft-ietf-cellar-matroska-control and draft-ietf-cellar-matroska-chapter-codecs are adopted but not yet tied to specific milestones or timelines.

• FFV1 Version 4 (draft-ietf-cellar-ffv1-v4):

  • Discussion on the scope and design principles for FFV1v4.
  • A proposal was made to publish FFV1v4 primarily as a "cleanup" version, removing historical accommodations and clarifying the specification, even without new features.
  • However, the consensus of the group, aligned with previous discussions, was to avoid multiple compatibility-breaking versions. Therefore, FFV1v4 should combine necessary fixes for V3's accommodations with new features to break compatibility only once.
  • There is no immediate urgency for FFV1v4, as V3 is currently stable and widely used.
  • GPU acceleration was noted as a significant request; the design of FFV1v4 should consider how to make it more GPU-friendly, possibly by studying bottlenecks in existing GPU implementations of V3.
  • Michael Le Meer offered to start a pull request for the cleanup aspects of FFV1v4.

• FFV1 Odd Width/Height Clarification:

  • Jerome highlighted an issue with the FFV1 V3 specification's lack of clarity regarding odd width and height when chroma subsampling is used. This ambiguity can lead to compatibility breaks. There is an ongoing discussion on the FFMpeg devel list and a need to update the FFV1 V3 specification (possibly via errata or clarification in V4) to resolve this.

• Meeting Logistics:

  • One participant (Martin) reported issues joining the MeetEcho session via the link on the DataTracker. Chairs will investigate the consistency and functionality of the MeetEcho links provided on the DataTracker and agenda pages for future meetings.

Decisions and Action Items

• Decision: The draft meeting minutes from the October interim meeting are approved.
• Decision: FFV1 Version 4 will aim to combine V3 cleanup/fixes with new features into a single release to minimize compatibility breaks, rather than an intermediate "cleanup-only" version.
• Action Item (Chairs): Update milestones in the DataTracker for Matroska extension documents. Target draft-ietf-cellar-matroska-tags for completion by end of 2023. draft-ietf-cellar-matroska-codec timeline to be determined (TBD). draft-ietf-cellar-matroska-control and draft-ietf-cellar-matroska-chapter-codecs will remain adopted drafts not yet tied to milestones.
• Action Item (Steve): Regenerate the expired Matroska drafts (draft-ietf-cellar-matroska-codec, draft-ietf-cellar-matroska-control, draft-ietf-cellar-matroska-chapter-codecs, draft-ietf-cellar-matroska-tags) to keep them active in the DataTracker.
• Action Item (Steve): Contact Moritz to gauge his availability and interest in taking the lead on the draft-ietf-cellar-matroska-codec specification.
• Action Item (Michael Le Meer): Create a pull request to start work on incorporating V3 specification cleanup (removing exceptions/accommodations) into draft-ietf-cellar-ffv1-v4.
• Action Item (Chairs): Investigate potential issues with MeetEcho meeting links on the DataTracker and agenda pages to ensure consistent and reliable access for participants.

Next Steps

• Continue development and refinement of the Matroska extension documents, prioritizing draft-ietf-cellar-matroska-tags.
• Address the normative down-reference in the FLAC specification based on ISG consultation.
• Advance draft-ietf-cellar-ffv1-v4, focusing on integrating V3 fixes and new features, with consideration for GPU-friendly design.
• Resolve the clarity issues in the FFV1 V3 specification regarding odd width/height with chroma subsampling.