draft-ugur-moq-fast-switching-00 | Individual submission | -00 posted 2026-10-13 | 13 pages | Standards Track | Datatracker
Authors
- Deniz Ugur (Ozyegin University)
- Zafer Gürel (Ozyegin University, moqtail)
- Ali C. Begen (Networked Media)
Abstract
A standards-track moq-transport technique that lets a subscriber switch between tracks encoded at the same bitrate but with different keyframe (GoP) intervals, getting both the compression efficiency of a long GoP and the switching responsiveness of a short GoP. The problem it addresses is a classic ABR tension: long GoPs compress better but force a subscriber to wait for the next keyframe before it can change renditions, while short GoPs switch fast but waste bits. This draft keeps multiple keyframe variants per bitrate and lets the subscriber pick the variant that makes the next switch happen soonest — then fall back to the efficient long-GoP variant once it has caught up.
Key Technical Details
- Switch Sets and the GoP Ladder. A publisher packages related tracks into a “Switch Set” identified by a common
altGroupidentifier. Within a single bitrate, a “GoP Ladder” holds several tracks that differ only in keyframe interval. Publishers advertise keyframe spacing in the catalog, so a subscriber can reason about switch opportunities without decoding. - Aligned Group IDs → comparable Frame Numbers. Tracks in a Switch Set align their Group IDs, which lets a subscriber compute a Frame Number that is comparable across every track in the set. That shared coordinate is what makes a clean cross-track switch point identifiable.
- Subscriber-side switch-point computation. The subscriber (not the publisher) computes the optimal switch point — the earliest aligned boundary at which the target track has a keyframe — and executes the transition with a
SUBSCRIBEorREQUEST_UPDATEcarrying theSWITCH_FROMsoft-mode parameter targeting that point. This reuses the existing SWITCH_FROM mechanism rather than inventing a new control message. - Combines long- and short-GoP strengths. By keeping both a long-GoP (efficient) and short-GoP (agile) variant at each bitrate and switching into the short variant only when a fast change is needed, the client gets responsive adaptation without paying the steady-state bitrate cost of universally short GoPs.
Relationship to other work
- A media / ABR building block built on SWITCH_FROM. It is an explicit client-driven use of the SWITCH_FROM soft-mode parameter that the WG settled in June 2026, extended to the keyframe-interval dimension rather than just the bitrate dimension — squarely in the wiki’s media focus area. Where moq-probing measures whether a hop can carry more, this draft governs how to move between representations once that decision is made.
- Adjacent to the live track-selection debate.
SWITCH_FROMis one of the three mechanisms Cullen Jennings’s #1982 (“selection sets and policy”) proposes to unify (alongside Top-N and SSTS; see also Mo Zanaty’s Top-Tracks-Filter #1981) — so this draft is a concrete consumer of exactly the primitive that debate is reshaping, posted during the same Seattle interim. - Authored by the moqtail / Ozyegin team. Deniz Ugur, Zafer Gürel and Ali C. Begen — the second media-focused individual input from this group this week, right after [[moq-probing|
draft-gurel-moq-probing-00]] (Oct-12). It is now the newest MoQ document on the datatracker (Oct-13).
Notes
Individual submission by Deniz Ugur, Zafer Gürel and Ali C. Begen; not WG-adopted. Posted 2026-10-13, during the Oct 12–15 Seattle hybrid interim. See adaptive-bitrate, switch-abr, moq-transport, moq-probing, moqtail, catalog-format, discussions-2026-10.