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fix(hls): never hold a DASH manifest on one rendition init - #6771
Broadcaster::manifest now reports current state. For each enabled rendition it starts any missing init build in the background, then lists only the renditions whose init already exists. A later refresh picks up the rest. The serve path's build_inits is gone. It used to await every rendition's init one after another, disabled ones included, so an inline-codec rendition bootstrapping from a still-open group could hold up the whole manifest.
Rendition::start_init takes the per-rendition building lock before it spawns. Each rendition gets at most one background build, and repeated renders never queue tasks behind a stuck one. A disabled rendition never starts a build.
The inline-init bootstrap now prefers the newest keyframe group whose timeline span already reached a later group. That group is closed, so the build is a cache read. Only after that does it try the newest group, which may still be open, and it moves on to the next candidate when one is gone from the cache. This applies to every caller, so the first HLS playlist builds sooner too.
The manifest route waits until one enabled video rendition has an init and is listable. The wait itself starts each video's build on every wake, so a video whose timeline arrives mid-wait still builds in time. The wait is bounded by the route's existing READY_TIMEOUT, with no new constant. Any one video init ends the wait, so a stuck rendition never holds a sibling that can play. This mirrors the HLS master's advertised() wait. A video whose listings refuse (denied media, a failed own or reference timeline) is left out of the wait, and one that starts refusing mid-wait drops out, so a broadcast with only audio playable is served at once.
The rendition's run state moves from a Mutex to a kio::Producer, so caching an init wakes that wait.
load_init and the background build share bootstrap, so HLS playlists, segments, and the init route otherwise behave as before.
Tests (mocked time):
the_first_manifest_lists_inline_video (server): a fresh edge's first manifest.mpd request lists an inline-codec video rendition. It fails on the previous head with a 404.
an_init_bootstraps_from_a_closed_group: the newest record is split inside an open group, and the manifest lists the rendition anyway. It fails on ac3115d4c8.
a_stuck_init_leaves_the_manifest_to_its_siblings: the only readable keyframe group is open. video_init resolves at once on the sibling's init, the sibling renders, and the stuck rendition is listed after its group closes.
a_disabled_rendition_never_builds_its_init: no build runs while the rendition is disabled, and it builds once re-enabled.
the_first_video_wait_builds_an_init_indexed_while_waiting: an inline video has nothing indexed when the wait starts. Its timeline arrives mid-wait, and the wait builds its init and resolves. It times out when builds start only once, before the wait.
a_denied_video_never_holds_the_manifest (server): with audio and a denied video, the first manifest.mpd lists audio without waiting out READY_TIMEOUT. It waits 5 s without the refusal filter.
a_refusal_wait_wakes_on_a_timeline_failure: a parked refusal wait wakes when either timeline fails.
a_blocked_init_bootstrap_does_not_hide_a_cached_init is rewritten. Its old fixture blocks only on an open trailing group, which the bootstrap now skips. The new fixture starts the build while only an open group is indexed.
Impact
Public API: none. Broadcaster::manifest keeps its signature. It now spawns builds onto the ambient tokio runtime, which Broadcaster::new already requires.
Wire: none.
Choices made
Where the first-video wait starts init builds (maintainer decision, after review round 5 found builds that never started for media indexed mid-wait):
✅ Start builds from inside the wait's poll, so every wake retries. The one-shot loop in Broadcaster::video_init is deleted.
Drop the first-manifest wait entirely. Kept in reserve: if the next review finds another gap in this wait, the plan is to drop it rather than patch it again.
The first manifest waits for one video init. A player keeps the adaptation sets of the first MPD it loads. Without this wait, a fresh edge's first manifest always lacked inline-codec video: the build it started could not finish before the render, as measured with a mocked-time test. The wait resolves at once when any enabled video rendition has an init or none is enabled, and gives up at READY_TIMEOUT. Alternatives considered:
Ship without the wait. The first MPD on a fresh edge has no inline video until the next refresh, and whether video ever shows up depends on how the player handles an AdaptationSet that appears in a later MPD.
Wait for every enabled rendition's init under the deadline. The audit rejected this: one stuck rendition holds the first manifest for the full timeout.
Init route left blocking. The quest says the /init.*.mp4 route "answers only once the init exists". I read that as: it keeps building its own init on request. Instance URLs are meant to be identical on every edge, so a player can ask one edge for an init that another edge listed. A route that refused to build would 404 there. It only waits on its own resource, never on a sibling's.
Rendering the manifest used to await every rendition's init serially,
disabled ones included, so an inline-codec rendition bootstrapping from a
still-open group held up the whole manifest. Rendering now starts each
enabled rendition's missing init in the background (one build at a time
per rendition) and lists only the renditions whose init exists; a later
refresh picks up the rest.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Manifest rendering now starts missing rendition init builds in the background and omits renditions until their init is known. The manifest route waits up to READY_TIMEOUT for a listable video rendition. Init bootstrapping can use ordered keyframe-group candidates. The changes also add coverage for pending builds, authorization failures, run changes, and cached init data. The M1 required-list entry and design note for DASH init readiness were removed.
Priority: Normal
Merge Risk: Low · up to bce66
An audio-only broadcast can return 404 on its first manifest request while its audio initializes. Add audio readiness for broadcasts without eligible video before merging.
Pre-merge checks: 4 · 1
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Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 63 functions across 6 files.
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Passed checks: 4 passed
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Title check
The title clearly identifies the main change: preventing a DASH manifest from waiting on one rendition's initialization.
Description check
The description directly explains the background initialization, manifest wait behavior, bootstrap changes, tests, and impact described by the changeset.
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kixelated
changed the title
A DASH manifest never waits on one rendition's init
fix(hls): never hold a DASH manifest on one rendition init
Oct 25, 2026
The nonblocking, per-rendition initialization direction is appropriate, and acquiring the build lock before spawning avoids queued duplicate work. Two issues remain, already reported independently:
P1, background-build lifetime: the detached task retains its rendition while an open group stalls, preventing teardown and causing Broadcaster::drop to retain the timeline watcher. Give initialization an owner-bound cancellation lifecycle. #6771 (comment)
P2, premature static manifest: an ended broadcast can emit a static audio-only MPD before the inline video init finishes, preventing clients from refreshing to discover video. Keep it refreshable while eligible initialization remains pending. #6771 (comment)
The added tests cover live sibling availability and disabled/re-enabled renditions, but not teardown cancellation or cold initialization after the broadcast ends.
Verification: static inspection of the patch, manifest rendering, initialization, and teardown paths. Tests were not run.
The init bootstrap read the newest indexed keyframe group, which can be
the one the publisher is still writing, so the build waited out the
group. It now tries the newest keyframe group whose span already reached
a later group first, then the newest one, and moves on when a candidate
is gone from the cache.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A player keeps the adaptation sets of the first manifest it loads, and a
fresh edge's first render lacked any inline-codec video because the init
build it started could not finish before the render. The manifest route
now starts every enabled video rendition's build and waits, within its
existing READY_TIMEOUT, until one of them has an init. Any single built
video init ends the wait, so a stuck rendition never holds a sibling.
The run state moves onto a kio producer so caching the init wakes it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Compared with reviewed ac3115d. Preferring an indexed closed keyframe group and bounding the first-video wait are useful improvements. Two new readiness problems are independently reported and confirmed:
P2: catalog closure finishes video_init despite pending initialization, so retained video-only recordings can initially return 404. Keep waiting on existing renditions after catalog closure. #6771 (comment)
P2: an initialized sibling with no listable segments releases the wait before playable inline video initializes. Gate readiness on a listable video representation, not just init bytes. #6771 (comment)
Prior findings remain open: detached initialization retains its owner, and static/dynamic calculation ignores enabled renditions with pending init. The any-video wait mitigates some cold starts but does not fix either: #6771 (comment) #6771 (comment)
Verification: static review of the incremental diff, kio closure semantics, and manifest/init paths. Tests were not run.
… a listable video
- The build holds only owned media handles and a weak rendition, and is aborted when the
rendition drops, so a build parked on an open group no longer keeps a torn-down export
(or its timeline watcher) alive.
- A manifest stays dynamic while an enabled rendition's init is still building.
- The first-manifest wait needs an advertised video with its init, and keeps waiting after
the catalog closes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
No new actionable bugs found. The four earlier findings are addressed: background-build lifetime, premature static manifests, readiness after catalog closure, and initialized-but-unlistable video. Compared against prior reviewed dec12ce, separating upstream changes.
Direction: weak ownership plus drop cancellation bounds initialization lifetime, pending builds preserve MPD refreshes, and readiness requires listable video. Owned initialization-read state is justified by cancellation requirements; regression tests target the earlier failures.
Verification: static incremental and surrounding initialization, readiness, manifest and teardown inspection. Tests were not run.
Landing: merged main (resolved the test-fixture conflict with #6464Publication API) and fixed all four review findings in 82d92bf. Codex (thumbs-up) and the OpenAI review of 82d92bf found nothing new. cargo test -p moq-hls --all-features, clippy, and quest check --base origin/main pass.
A background init build parked on the old run's open group kept holding
the build lock after a restart, so the new run could never start its own
and stayed out of the manifest. Restarting now aborts it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
No new actionable bugs found. This update addresses the independently reported previous-generation init lock #6771 (comment): Rendition::restart aborts its background initialization before clearing the old run, allowing cancellation to release the build lock. Earlier reviewed lifecycle, readiness, and static-manifest fixes remain intact.
Direction: reusing the existing owner-held task handle is a focused fix without extra machinery. The new regression test exercises cancellation while the old group remains open; it checks lock release rather than complete initialization of the replacement generation.
Verification: static inspection of the incremental fix and restart/build lifecycle, separating the preceding upstream merge from prior reviewed 82d92bf. Tests were not run.
The synchronous manifest render started the init build with tokio::spawn,
which panics when an embedder renders from a thread outside the runtime.
A rendition now keeps the handle of the runtime it was built on, where
its timeline watcher already runs, and spawns the build there.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
No new actionable bugs found versus 0c9f768. The independently reported off-runtime render panic #6771 (comment) is addressed: initialization uses the rendition's captured runtime handle rather than requiring runtime context on the synchronous rendering thread. Earlier cancellation and readiness fixes remain intact.
Direction: this is a focused fix within the export's existing Tokio-owned watcher lifecycle. It does not implement the broader poll-first/kio architecture preferred by rs/AGENTS.md; that remains architectural follow-up rather than a remaining instance of this panic.
Verification: static inspection of the delta, rendition construction/registration, and spawning paths. The added plain-thread test covers the reported panic and build startup; tests were not run.
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Exclude independently failed videos from the init wait
When audio is playable but every enabled video has an independently failed timeline or an unauthorized media reference, this filter still includes those videos even though poll_advertised() can never report them ready. Consequently, server/routes.rs::manifest waits for its full five-second timeout on every MPD request before serving the available audio. Previously, build_inits() could return immediately for these terminal failures, and Broadcaster::manifest() already excludes them via failed_alone(). Exclude independently failed videos from this readiness gate, and observe failures that occur while waiting, so unavailable video does not repeatedly delay healthy audio.
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Agreed, this is a regression from the poll_advertised gate added in 82d92bf. A video that failed on its own (failed_alone) or is unauthorized can never become advertised, so the first-video wait runs to its timeout on every MPD request. The fix is to leave those renditions out of the video_init gate, and to re-check while waiting. That would be a fourth fix round on this PR, so I am handing it back to the maintainer instead of landing it. Everything else through 0e71d40 has clean reviews.
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Fixed in e46e2ec. The video_init gate now leaves out any video whose listings refuse (Rendition::check): denied media, its own failed timeline, or a failed reference, which makes the manifest error at once instead of after the timeout. The new Rendition::poll_refused registers on the media binding and on both timelines' failures, so a video that starts refusing mid-wait drops out of the gate too.
a_denied_video_never_holds_the_manifest (routes): audio plus a denied video; the first manifest.mpd lists audio well under READY_TIMEOUT. Without the gate change it waits 5 s.
a_refusal_wait_wakes_on_a_timeline_failure: a parked wait wakes when either timeline fails. Without the timeline registrations it never wakes.
A video whose media is denied or whose timeline failed can never be
listed, so counting it made every MPD request wait out READY_TIMEOUT
when only audio was playable. The wait now skips any rendition whose
listings refuse, and wakes when one starts refusing mid-wait.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Start missing init builds when video timelines become available
On a cold request where audio is already playable but the inline-codec video's timeline has not arrived, this one-time start_init() call returns without spawning anything because init_read() has no candidate groups. If the video timeline and cached media arrive during the subsequent wait, renditions.video_init() only checks readiness and never starts the now-buildable init. The request therefore waits the full five-second timeout, after which manifest() starts the build but immediately returns an audio-only MPD. Drive init startup from the readiness wait as candidates become available so usable video can satisfy the wait instead of introducing a timeout and still missing the first response.
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Agreed. start_init runs once before the wait, so a video whose timeline or cached media arrives during the wait is never built, and the request times out into an audio-only MPD. The fix is to call start_init from the video_init poll itself, next to the readiness check. That re-runs it on every wake (new rows, resolved spans), and the one-shot loop in Broadcaster::video_init goes away. It would be the fifth fix round on this wait, so I am handing the design call back to the maintainer instead of pushing it.
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Fixed in bce6607, on the maintainer's go-ahead. The video_init poll now calls start_init on each eligible video before checking readiness, so it runs again on every wake. The one-shot loop in Broadcaster::video_init is gone. The wake comes from poll_refused, which already registers the waiter on both timelines, so the rows a build needs wake the wait to start it.
the_first_video_wait_builds_an_init_indexed_while_waiting starts the wait while the inline video has nothing indexed, then publishes its closed groups and timeline. The wait resolves at once. On the previous head it times out.
The wait started each build once, up front, so an inline video whose
timeline arrived mid-wait never built its init and the request timed out
into an audio-only manifest. The wait now starts builds on every wake.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Fixed the round-4 finding: the first-video wait leaves out videos whose listings refuse (denied, or a failed timeline) and wakes when one starts refusing.
Fixed the round-5 finding, per the maintainer's ✅ in the PR body: the wait starts init builds on every wake, so media indexed mid-wait still builds in time.
Each fix has a test that fails without it. just check passes locally, required CI passes, and Codex gave the head a 👍.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @rs/moq-hls/src/server/routes.rs:
- Around line 92-100: Update the readiness flow before
`broadcaster.manifest(query)` to wait for an audio init when no eligible video
exists, so audio-only broadcasts do not render the manifest before audio
initialization completes. Preserve the current video-first behavior for
broadcasts with playable video siblings.
After applying the fix, consider running `coderabbit review --agent` for local
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Reviewing files that changed from the base of the PR and between aa81e59 and bce6607.
Files selected for processing: 8
quest/m1/README.md
quest/m1/dash-init-ready.md
rs/moq-hls/src/export/mod.rs
rs/moq-hls/src/export/rendition.rs
rs/moq-hls/src/export/renditions.rs
rs/moq-hls/src/export/segments.rs
rs/moq-hls/src/export/spans.rs
rs/moq-hls/src/server/routes.rs
Files with no reviewable changes: 2
quest/m1/README.md
quest/m1/dash-init-ready.md
Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 0 remain after this review.
Direction: driving initialization inside the readiness poll removes the one-shot startup gap, while existing timeline registrations trigger reevaluation and the build lock prevents duplicate work. Prior cancellation, static-manifest, and off-runtime fixes remain intact.
Verification: static incremental inspection since 0e71d40, excluding upstream changes, plus refusal and timeline-wakeup paths. Regression tests cover both fixes; tests were not run.
Ports #6771's background init builds and first-video manifest wait onto the
HLS records: init groups come from listed rows, a complete group (one a later
segment followed) before one only a stop bounds, and its tests use hand
published records.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Finishes
quest/m1/dash-init-ready.md.Summary
Broadcaster::manifestnow reports current state. For each enabled rendition it starts any missing init build in the background, then lists only the renditions whose init already exists. A later refresh picks up the rest. The serve path'sbuild_initsis gone. It used to await every rendition's init one after another, disabled ones included, so an inline-codec rendition bootstrapping from a still-open group could hold up the whole manifest.Rendition::start_inittakes the per-renditionbuildinglock before it spawns. Each rendition gets at most one background build, and repeated renders never queue tasks behind a stuck one. A disabled rendition never starts a build.READY_TIMEOUT, with no new constant. Any one video init ends the wait, so a stuck rendition never holds a sibling that can play. This mirrors the HLS master'sadvertised()wait. A video whose listings refuse (denied media, a failed own or reference timeline) is left out of the wait, and one that starts refusing mid-wait drops out, so a broadcast with only audio playable is served at once.Mutexto akio::Producer, so caching an init wakes that wait.load_initand the background build sharebootstrap, so HLS playlists, segments, and the init route otherwise behave as before.Tests (mocked time):
the_first_manifest_lists_inline_video(server): a fresh edge's firstmanifest.mpdrequest lists an inline-codec video rendition. It fails on the previous head with a 404.an_init_bootstraps_from_a_closed_group: the newest record is split inside an open group, and the manifest lists the rendition anyway. It fails onac3115d4c8.a_stuck_init_leaves_the_manifest_to_its_siblings: the only readable keyframe group is open.video_initresolves at once on the sibling's init, the sibling renders, and the stuck rendition is listed after its group closes.a_disabled_rendition_never_builds_its_init: no build runs while the rendition is disabled, and it builds once re-enabled.the_first_video_wait_builds_an_init_indexed_while_waiting: an inline video has nothing indexed when the wait starts. Its timeline arrives mid-wait, and the wait builds its init and resolves. It times out when builds start only once, before the wait.a_denied_video_never_holds_the_manifest(server): with audio and a denied video, the firstmanifest.mpdlists audio without waiting outREADY_TIMEOUT. It waits 5 s without the refusal filter.a_refusal_wait_wakes_on_a_timeline_failure: a parked refusal wait wakes when either timeline fails.a_blocked_init_bootstrap_does_not_hide_a_cached_initis rewritten. Its old fixture blocks only on an open trailing group, which the bootstrap now skips. The new fixture starts the build while only an open group is indexed.Impact
Broadcaster::manifestkeeps its signature. It now spawns builds onto the ambient tokio runtime, whichBroadcaster::newalready requires.Choices made
Where the first-video wait starts init builds (maintainer decision, after review round 5 found builds that never started for media indexed mid-wait):
Broadcaster::video_initis deleted.The first manifest waits for one video init. A player keeps the adaptation sets of the first MPD it loads. Without this wait, a fresh edge's first manifest always lacked inline-codec video: the build it started could not finish before the render, as measured with a mocked-time test. The wait resolves at once when any enabled video rendition has an init or none is enabled, and gives up at
READY_TIMEOUT. Alternatives considered:Init route left blocking. The quest says the
/init.*.mp4route "answers only once the init exists". I read that as: it keeps building its own init on request. Instance URLs are meant to be identical on every edge, so a player can ask one edge for an init that another edge listed. A route that refused to build would 404 there. It only waits on its own resource, never on a sibling's.🤖 Generated with Claude Code
(Written by Claude Opus 5.5)