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Low Overhead Media Container (LOC)

5 min read

draft-ietf-moq-loc-04 | published 2026-07-20 | 20 pages | Datatracker draft-ietf-moq-loc-03 | published 2026-07-06

Authors

Abstract

LOC presents a container format for encoded audio and video media intended primarily for interactive streaming over QUIC. It emphasizes minimal encapsulation overhead and compatibility with WebCodecs standards.

Key Features

  • Minimal overhead: Designed for low-latency interactive use cases
  • WebCodecs compatible: Aligns with browser WebCodecs API
  • Codec agnostic: Metadata properties for both audio and video
  • E2E encryption: Supports moq-secure-objects integration
  • Extension mechanism: Header extensions for timestamps, video frame marking, audio level

Extensions (draft-02)

LOC uses numbered extensions in the object header:

  • Timestamp
  • Video Frame Marking (ID=4)
  • Audio Level
  • Note: Issue #13 - Duplicate extension ID (0x06) for Timestamp and Audio Level

Recent Highlights

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

  • draft-04 published (2026-07-20) — the first revision after IANA’s July-16 early review of loc-03. It fixes the MoQ Properties IANA registry (loc #28, Mo Zanaty, +15/−17), coordinated with the twin [[moq-transport|moq-transport #1818]] “Fix IANA Properties for LOC/SecureObjects” fix — the six LOC properties are now registered at IDs 0x08 / 0x09 / 0x0C / 0x0D / 0x0F / 0x10, moving TIMESTAMP off the 0x06 value that collided with MoQ SUBGROUP_DELIVERY_TIMEOUT (building on loc #27’s July-19 TIMESTAMP-value bump). Resolves the registry name/reference mismatches IANA flagged (see loc #26). Landed the morning of the IETF-126 Monday session.

  • draft-03 published (2026-07-06) — the first LOC revision since -02; adds an audio-configuration structure and revises all audio config (PR #24), resolving the June audio-config gap.

  • Cross-spec property-ID coordination dispute: moq-transport-18 §15.8-2 and draft-ietf-moq-loc-02 diverge on Property Type IDs (MOQ-18 TIMESTAMP=0x06 / TIMESCALE=0x08 / AUDIO_LEVEL=0x0C / VIDEO_FRAME_MARKING=0x0A / VIDEO_CONFIG=0x0D vs LOC-02 TIMESTAMP=0x02 / AUDIO_LEVEL=0x06 / VIDEO_FRAME_MARKING=0x04) — the first post-draft-18 cross-spec coordination failure, with a twin moq-transport issue; the provisional IANA registry for LOC properties did not propagate into the draft-18 assignments. LOC is also moving its own TIMESTAMP off 0x06 because it collides with MoQ SUBGROUP_DELIVERY_TIMEOUT.

  • First LOC encoder/decoder library shipped in the moq stack (moq-loc Rust crate + @moq/loc JS package, integrated into moq-mux + hang catalog + watch player). It chose the moq-transport-18 §15.8 property IDs (TIMESTAMP=0x06, TIMESCALE=0x08) over the conflicting historical loc-02 values (TIMESTAMP=0x02) — a vote-with-code making moq-dev/moq the de facto reference for post-draft-18 property assignments until a draft-ietf-moq-loc-03 aligns them. Catalog timescale defaults to 1,000,000 µs with per-frame override via the 0x08 property; LOC is prioritized after legacy, before CMAF, in audio source selection.

  • LOC private-properties encoding is underspecified: the draft does not say how private properties behave when absent — omit the block entirely vs write a zero-count varint. Surfaced under live two-impl media interop; imquic resolved it implementation-side by writing an explicit payload prefix for LOC private objects.

  • No audio config property: LOC defines a Video Config property for video decoder setup but has no audio equivalent, leaving codec-specific init data (e.g. AAC’s AudioSpecificConfig) without a standard place and not fully captured by the codec string.

  • Other open design topics: moving redundant properties in the catalog, delta-compressing timestamps, Unix epoch + Timescale, Video Frame Marking vi64 encoding ambiguity, WebCodecs avc3/hev1 formats, track-property authentication, and moving LOC header metadata from object-header extensions to the object payload.

  • Draft status: the published text is now draft-ietf-moq-loc-04 (2026-07-20); several of the design-tension items above (property-ID coordination, audio config, IANA registry names) were folded into the -03/-04 revisions, while the open topics (delta-compressed timestamps, VFM vi64 encoding, track-property authentication) remain design inputs. A new loc issue “Frame durations and discontinuities” was opened during IETF-126 week (per the July-19 weekly GitHub digest).

Related

Design Tension: LOC vs CMAF

LOC represents the “low overhead” approach optimized for interactive/real-time use cases, while moq-cmsf provides CMAF compatibility for traditional OTT streaming. luke-curley has proposed CMAF compression as a potential bridge between the two approaches.

Implementation tracking

  • moqtail — full LOC encode/decode in moqtail-rs (sample app + draft-16 catalog plumbing).
  • moqlivemock / warp-player (Eyevinn) — LOC pipeline added in v0.8.0 (May 5, 2026), including HEVC LOC and a WebCodecs LOC pipeline.
  • moq-dev (Luke Curley) — PR #1388 OPENED May 7 2026 (+799/−17, link). New moq-loc Rust crate + @moq/loc JS package implementing encode/decode for the LOC wire format. Hang catalog gains Container::Loc { timescale } (default 1,000,000 µs); audio source selection prioritizes LOC after legacy, before CMAF. First adoption of an IETF-spec media container format in moq-dev/moq alongside its native Hang stack. Per-frame timescale (0x08 property) overrides catalog default. On 2026-07-31 moq-dev began adopting the draft-ietf-moq-loc-04 Timestamp code point (#2578 merged + OPEN #2581) — moving its LOC implementation off the interim transport-18 §15.8 property IDs onto the -04 registry that relocated TIMESTAMP off the 0x06 collision, the implementation now following the published -04 in code.

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