fix(playback): make HLS variable substitution opt-in - #218
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Transcode playback on the Tizen TV app 401'd on every segment: large
synthetic manifests (any feature-length title) carried their access
query once through #EXT-X-DEFINE and wrote segment URIs as
?{$silo_query}. AVPlay, like most native HLS stacks, ignores the tag and
requests the literal URI without the st stream token. The substitution
came in with the upstream sync (#174) for hls.js parsing speed.
Only a client that declares hls_variable_substitution_v1 now gets the
compact form. The plan's HLS manifest URL carries a non-secret
hls_vars=1 flag, read from the manifest request's raw query, so the
opt-in survives token reconstruction, the API relay to a transcode node
(which strips only st) and proxy token/grant routes without session
state. Every other client gets the legacy per-segment query again.
The web player advertises the feature only when it expects to play
through hls.js (non-Safari with Media Source); Safari stays native.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe player advertises HLS variable-substitution support when hls.js is expected. The server adds an opt-in query parameter to eligible HLS manifest URLs. Large synthetic manifests use query-variable substitution only when the request opts in and existing checks pass. ChangesHLS query variable substitution
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant PlaybackClient
participant PlaybackAPI
participant SyntheticManifest
PlaybackClient->>PlaybackAPI: Send playback request with client feature
PlaybackAPI-->>PlaybackClient: Return HLS manifest URL with hls_vars=1 when eligible
PlaybackClient->>SyntheticManifest: Request manifest with query parameter
SyntheticManifest-->>PlaybackClient: Return manifest using query substitution when eligible
Suggested reviewers: Merge Risk: 🟡 Moderate · up to Native HLS fallback can fail playback when it receives a substituted manifest. Ensure fallback uses a non-substituted URL before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change controls playlist formatting rather than media-access permissions. Existing authentication remains in place, and clients without the capability receive the legacy format. Compatibility still depends on accurate capability advertising and preserving the format of already-issued URLs. Retained concerns Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
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Inline comments:
Review comments at @web/src/player/utils/hlsEngine.ts:
- Line 34: Update the native fallback in resolveHLSEngineV3 to remove hls_vars=1
from the manifest URL before assigning it to video.src; keep the substituted URL
behavior for hls.js unchanged.
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📒 Files selected for processing (17)
contracts/api/v2/openapi.jsondocs/architecture/playback-protocol-v3.mdinternal/api/handlers/playback_v3.gointernal/api/handlers/playback_v3_test.gointernal/apiv2/playback_delivery.gointernal/playback/protocol_v3.gointernal/playback/transcode.gointernal/playback/transcode_manifest_test.gointernal/transcodenode/streaming_protocol.goscripts/prairie-invariants.txtweb/src/api/v2/schema.tsweb/src/player/hooks/usePlaybackSession.test.tsweb/src/player/hooks/usePlaybackSession.tsweb/src/player/playback-session-wire-v3.tsweb/src/player/protocol-v3.tsweb/src/player/utils/hlsEngine.test.tsweb/src/player/utils/hlsEngine.ts
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The plan opts into HLS variable substitution because the web client predicted hls.js. If hls.js then fails to load, VideoPlayer falls back to the media element, which may not implement #EXT-X-DEFINE. Strip hls_vars=1 from the URL on that path so the server serves the legacy manifest. Also refresh the system-info fixture's contract_digest for the updated OpenAPI artifact. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
1 participant
Symptom
Transcode playback on the Samsung Tizen TV app is broken for any feature-length title. The master playlist loads (200), but every segment request returns 401
authentication_required, retried every 4 s for the whole session.Cause
Since the upstream sync (#174), large synthetic manifests move the access query into
#EXT-X-DEFINE:NAME="silo_query",...and write each segment URI asseg_NNNNN.ts?{$silo_query}, bumpingEXT-X-VERSIONto 8. hls.js expands the variable, but native HLS stacks such as the Tizen player don't. They request the literal URI, theststream token is dropped, and every segment 401s. The 163 KB manifest the TV received matches the substituted form exactly; with a per-segment token it would be over 1 MB.Fix
Variable substitution is now opt-in:
hls_variable_substitution_v1, lets a client say it supports substitution. When a client sends it, the server adds a non-secrethls_vars=1flag to the plan's HLS manifest URL. This happens at plan start and on replans that create a fresh transport; a replan that reuses a transport keeps its already-issued URL.syntheticManifestQueryuses the#EXT-X-DEFINEform only when the manifest request carrieshls_vars=1. Every other client gets the legacy per-segment query again.st), and proxy routes. It isn't signed and grants nothing, sostverification is unaffected.MediaSourceorManagedMediaSourceis available). Jellycompat and the TV apps never send it, so they get the legacy form.Notes for review
contracts/api/v2/openapi.jsonandweb/src/api/v2/schema.tswere edited by hand, because the generators couldn't run locally. Ifverify-apiv2-openapiorverify-apiv2-web-typesfails, regenerate them withmake apiv2-openapiandmake apiv2-web-types.#EXT-X-DEFINEis unverified.Tests
hls_vars=0orxhls_vars=1) has no#EXT-X-DEFINE, no{$and noVERSION:8, and repeats the query on every segment and init URI, for both.tsand.m4s.#EXT-X-DEFINEform now opts in.scripts/prairie-invariants.txtprotect the gate.🤖 Generated with Claude Code
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