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CMSF - CMAF Compliant MOQT Streaming Format

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draft-ietf-moq-cmsf-01 | 19 pages | Submitted 2026-06-03 | Datatracker

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Abstract

CMSF extends moq-msf by introducing CMAF-packaged media support. It describes the syntax and semantics for adding CMAF-packaged media to MSF, enabling delivery of CMAF and LOC-compliant content over moq-transport while maintaining all existing MSF capabilities.

Relationship to MSF and LOC

  • moq-msf is the base streaming format
  • moq-loc is the low-overhead container for interactive use
  • CMSF adds CMAF packaging for traditional OTT/broadcast workflows
  • All three work together: CMSF inherits MSF’s catalog, timeline, ABR, and LOC support

Design Tension

The MOQ ecosystem has two container philosophies:

  1. LOC - Minimal overhead, WebCodecs-native, optimized for real-time
  2. CMAF - Industry standard for OTT, broad tooling support, higher overhead

CMSF bridges this by allowing CMAF content to flow through the same MSF infrastructure alongside LOC content. luke-curley’s compressed-mp4 proposal is another approach to reduce CMAF overhead.

See media-packaging for a full comparison.

History

CMSF originated as draft-law-moq-carp-00 (“CARP - a CMAF compliant implementation of WARP”) submitted by will-law in November 2025. The draft was adopted by the MOQ working group and published as draft-ietf-moq-cmsf-00 in December 2025. The first revision, draft-ietf-moq-cmsf-01 — the first since -00 — was submitted to the Datatracker in June 2026.

ContentProtection Signaling

PR #18 (merged Apr 14 by will-law) added ContentProtection signaling to the CMSF spec. The design, proposed by Torbjörn Einarsson (Eyevinn), is roughly based on DASH/DASH-IF content protection signaling:

  • Defines contentProtections as a top-level array of protection descriptors with refIDs in the catalog
  • Each encrypted track references applicable protections via a contentProtectionRefIDs array
  • Supports the same attributes as DASH/DASH-IF: Widevine, PlayReady, FairPlay, and ECCP (clear key)
  • Addresses issue #8

Implementations:

Key rotation is not yet defined — future work can build on this for live catalogs with new refIDs.

Recent Highlights

Day-by-day WG/PR activity lives in the wiki log; this section keeps only durable milestones.

  • LOCMAF adopted as a locmaf packaging — by reference: CMSF PR #27 registers a third locmaf packaging mode (between cmaf full-chunk passthrough and loc codec-elementary frames) by normative reference to the standalone LOCMAF draft rather than folding the format text in — so CMSF now spans cmaf / locmaf / loc while LOCMAF stays a sovereign individual draft. The locmaf mode carries tagged fields plus unmodified samples so the receiver reconstructs the same CMAF chunk while dropping steady-state overhead to a couple of bytes.
  • Dual Track+Object initData: Will Law’s design carries init data via both a stable Track property (steady-state init) and an Object property for synchronized mid-track changes such as DASH-period switches and DRM key rotation.
  • First working CMSF muxer/demuxer in a tracked open-source MoQ implementation landed in moq, under the principle “CMSF is CMAF with a different catalog format” — a hang::Catalog intermediate representation serializes to MSF or Hang catalog formats.
  • emsg signaling design: catalog signaling of EMSG presence so players know to parse ISO boxes, a per-track scheme_id_uri indicating the payload, and multiple emsg tags per track.
  • Zapping / fast-switching: a manifest parameter mimicking HESP, where one track carries more keyframes than others to enable fast switching.
  • Media-format landscape stratified by initData semantics: CMSF carries full CMAF chunks, LOCMAF delta-compresses CMAF chunk metadata, LOC strips fMP4 entirely, and MSFTS carries MPEG-TS.

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