fix(sfu): publish a single high representation (#248)

docs/project-memory.md

@@ -33,14 +33,14 @@ Last updated: 2026-08-25
 - Current source and production admit up to `20` Viewers and implement the uniform `1/2/3` endpoint cap, exact prepare candidate, first-decoded-frame commit, strict rollback revision, decoded-progress stall, a two-stage direct/SFU operation deadline, and one event-driven room controller. A short-lived exact-generation decoded-frame observer proves only the pending candidate inside the existing total deadline; the periodic stats sampler remains responsible for active-path diagnostics and stalls. Ordinary peer ICE is STUN-only and the sole application fallback is SFU/UDP; stale TURN environment keys fail startup. SFU admission uses exact publication and Viewer-subscription handles with explicit no-default ingress/egress capacities and a listener-fenced dedicated LiveKit owner. Browser SFU publisher/subscriber connects use fresh empty ICE-server options; the owner physically verified deployed SFU fallback media after release `c4962f5`, closing the prior core-route hold.
 - Source and production use random four-digit memory rooms, dormant leases, exact-Host resume, restart loss, local preference replay, orthogonal grants/code entry, and no SQLite runtime. V12 uses a 22-character room-incarnation grant, `ROOM_NOT_FOUND`, no diagnostic-file export, and a compact UI showing the complete shorter URL.
 - Exact production artifacts, services, ports, and any change-scoped infrastructure recovery boundary are owned by [deployment](./deployment.md) and indexed by [status](./status.md).
-- Source and production require v12, fixed VP8, and no video hint. Their SFU publisher still sends ordered `q,h` simulcast and is not yet aligned with accepted single `HIGH`. Current Pause/Resume, live audio ceilings, exact-sender metrics, relay/SFU audio continuity, typed Viewer presentation, and quality profiles match the product truths above.
+- Source and production require v12, fixed VP8, and no video hint. Current source publishes exactly one SFU `HIGH` encoding without simulcast or a subscriber layer selector; production still sends ordered `q,h` until the next application cutover. Current Pause/Resume, live audio ceilings, exact-sender metrics, relay/SFU audio continuity, typed Viewer presentation, and quality profiles match the product truths above.
 - Browser SFU subscribers reconcile eligible Host screen publications across connect/activate event ordering, participant/track arrival, and reconnect. Production LiveKit logs only warn/error, and the application service has a bounded same-host LiveKit readiness preflight.
 - Exact `main@bf32859` passed TypeScript, 613 Web tests, both builds, hygiene, review, and production postflight. Chrome 151 closed direct/browser-relay VP8 cadence and active-audio ceilings; its SFU A/B rejected always-active `LOW` without claiming a deployed single representation, public SFU 60 fps, or real-game synchronization. Exact metrics live in [verification status](./verification-status.md).
 - Chrome loopback, cap2/cap3, short resource, recovery, MBB, and A/V fixtures are bounded evidence only. They do not establish quality, resource limits, or product policy.
 
 ## Current Priority
 
-1. Implement, deploy, and physically verify the accepted single-`HIGH` Browser SFU publication; leave direct, browser-relay, content-hint, and routing behavior unchanged.
+1. Deploy and physically verify the current single-`HIGH` Browser SFU publication; leave direct, browser-relay, content-hint, and routing behavior unchanged.
 2. Then finish real-network route, recovery, screen-audio and real-game A/V acceptance. Browser VP8 hardware acceleration and mobile Viewer lifecycle remain Accepted Later; Native/executable, distribution, and repository-wide simplification remain later phases.
 
 The desktop Host background/minimized report is deferred until it reproduces on current production with a real game and synchronized media plus CPU/GPU evidence. The bounded current-Chrome screening found no immediate Host-page lifecycle drop, and removal of the old harmful `contentHint = "motion"` remains a plausible confound rather than a proven background fix. Mobile Viewer playback and assigned-relay survival remain a separate lifecycle gate.

docs/research/realtime-quality-adaptation.md

@@ -226,7 +226,7 @@ when a sender is installed; `LocalVideoTrack.publishOptions` drives encoding
 recomputation after a track restart; and `LocalTrackPublication.options` is the
 input to `republishAllTracks()`. Current source keeps those three owners aligned
 through the existing publisher operation queue and rollback: call the SDK
-preference API to update its saved state, configure/read back the current `q,h`
+preference API to update its saved state, configure/read back the exact single
 sender as the final write, then assign one merged option object to both retained
 locations. Failure reapplies the previous profile; generation loss cannot
 retain the result as current publisher state. This changes no capture
@@ -408,7 +408,7 @@ time deltas, `remoteId` linkage, and the selected path reached through that RTP
 stream's transport. Source replacement blocks sampling and invalidates in-flight
 generations. Direct/relay edges bind that evidence to the
 current track and PeerConnection. The Host SFU publisher also samples only its
-active LiveKit sender's `h` representation and binds the result again to the
+exact active LiveKit sender and binds the result again to the
 current publication generation; replacement, profile reset, retirement,
 disconnect, and authoritative resync clear the old identity before another
 sample can appear. The Host details UI renders that source once as `SFU 发送`,
@@ -443,11 +443,10 @@ one unambiguous encoding. Current quality settings do not request a mode, so
 the requested value remains null and a browser-reported default is not called
 a mismatch; multiple encodings remain unknown. Inbound stats provide no current
 standard `scalabilityMode` source, so C does not carry a null-only placeholder.
-Current source and production still configure the ordered `q,h` publication,
-but the exact-production gate above rejected it because the active lower
-representation reduced `HIGH`. ADR-0007 now accepts one Browser SFU `HIGH`;
-source implementation and the exact single-representation production gate are
-the next scoped work.
+The exact-production gate above rejected its ordered `q,h` publication because
+the active lower representation reduced `HIGH`. Current source now implements
+ADR-0007's one Browser SFU `HIGH`; production remains `q,h` until the exact
+single-representation deployment gate passes.
 
 Official W3C text checked 2026-08-19 defines names ending in `Id` as stats-object
 references. In particular, outbound [`mediaSourceId`](https://www.w3.org/TR/webrtc-stats/#dom-rtcoutboundrtpstreamstats-mediasourceid)

docs/session-handoff.md

@@ -58,7 +58,8 @@ Current high-signal boundary:
   three sender ceilings. An exact-production VP8 gate sustained about 59.5 fps
   on direct and Browser-relay paths and rejected the current SFU `q,h`
   publication because active `LOW` reduced `HIGH`. ADR-0007 accepts one Browser
-  SFU `HIGH`; source and production remain `q,h` until the next scoped change.
+  SFU `HIGH`; current source implements that single representation, while
+  production remains `q,h` until the next application cutover and physical gate.
 - Ordinary browser ICE owns direct reachability. Do not build port prediction,
   guessed candidates, NAT classification, TCP probes, quality scores, or
   quality-driven reparenting. Current-path quality is diagnostic; a healthy

docs/status.md

@@ -22,14 +22,14 @@ This is the current execution index. Git history owns completed timelines; [veri
 - One event-driven controller owns the committed graph and at most one room-serial child operation. It uses one deterministic candidate list/cursor and one total direct-then-SFU deadline; exact admission and physical resources remain charged through drain, and the pending candidate commits only after an exact-generation decoded-frame proof. A short-lived 100 ms stats observer proves only that candidate inside the existing deadline, while the 2-second sampler remains responsible for active-path diagnostics and decoded-frame stalls. Healthy edges remain sticky and current-path quality does not authorize reparenting.
 - Ordinary peer ICE is STUN-only and the only application fallback is the dedicated LiveKit SFU over UDP. SFU generations use explicit no-default ingress/egress capacities, exact `reserved | committed | draining` accounting, delete-plus-absence release, one Host publication, and exact Viewer subscription handles. No Screener TURN, ICE/TCP, media TCP, or TLS-relayed media route exists.
 - Current Browser SFU publisher and subscriber connects supply fresh `autoSubscribe: false` plus `rtcConfig: { iceServers: [] }` options. Ordinary peers retain deployment STUN; LiveKit signaling candidates, server-side public-IP discovery, route deadlines, ports, and retry behavior are unchanged.
-- Current source leaves video `contentHint` unset and keeps audio `contentHint = "music"`. Browser direct and browser-relay offers contain VP8 as their only media codec, and SFU publication explicitly uses VP8 with no backup codec. Codec UI, quality state, wire fields, fallback media codecs, and share-lifetime codec branches are absent. The SFU publisher still configures ordered `q,h` simulcast and is therefore out of alignment with ADR-0007's accepted single-`HIGH` representation until the next scoped source change. Live 64/128/256 kbps audio-ceiling mutation remains unchanged; ordinary Host and SFU publisher metrics select the exact current audio sender, relays reconcile audio-track additions and removals on the persistent stream, and an SFU reconnect reacquires the current publication/sender or fails the route closed.
+- Current source leaves video `contentHint` unset and keeps audio `contentHint = "music"`. Browser direct and browser-relay offers contain VP8 as their only media codec, and SFU publication uses exactly one VP8 `HIGH` encoding with `simulcast: false`, no backup codec, no subscriber quality selector, and explicit `dynacast: false`. Codec UI, quality state, wire fields, fallback media codecs, and share-lifetime codec branches are absent. Live 64/128/256 kbps audio-ceiling mutation remains unchanged; ordinary Host and SFU publisher metrics select the exact current sender, relays reconcile audio-track additions and removals on the persistent stream, and an SFU reconnect reacquires the current publication/sender or fails the route closed.
 - Current source implements typed first-frame Viewer presentation and recovery, Chinese user-facing route/access failures, local connection details without a diagnostic-file export, authenticated Host-only on-demand route snapshots for automatic acceptance, explicit missing-room presentation, and responsive entry controls. Host invitation controls remain independent from two-state room-code entry.
 - Recommended quality remains exactly `1080p60`, `1080p30`, and `720p30`; current source defaults to `1080p30`. Advanced resolution adds `480p` as `854x480` without adding a fourth preset, and advanced FPS and bitrate remain independent.
-- Exact `main@bf32859` passed repository hygiene, TypeScript, all 613 Web tests in 44 files, both production builds, focused independent review, and the production artifact/service postflight above. A Chrome 151 production gate then exercised two direct children, one browser-relay child, one SFU subscription, all three audio ceilings, and live source replacement with progressing audio/video. A separate exact-production VP8 gate sustained about 59.5 fps on direct and browser-relay paths, while its SFU A/B proved that the always-active `LOW` materially reduced `HIGH`; exact applicability remains in [verification status](./verification-status.md).
+- Current source passed repository hygiene, TypeScript, all 607 Web tests in 44 files, and both production builds. Exact production `bf32859` separately passed its recorded source and postflight gates. A Chrome 151 production gate exercised two direct children, one browser-relay child, one SFU subscription, all three audio ceilings, and live source replacement with progressing audio/video. A separate exact-production VP8 gate sustained about 59.5 fps on direct and browser-relay paths, while its SFU A/B proved that the always-active `LOW` materially reduced `HIGH`; the new single-representation source still requires exact deployed proof.
 
 ## Current Milestone
 
-1. Align Browser SFU publication with ADR-0007's accepted single-`HIGH` VP8 representation, deploy the exact artifact, and physically verify one outbound video encoding with progressing publisher/subscriber media. Direct and browser-relay VP8/no-hint performance is already closed by the exact-production gate.
+1. Deploy the current single-`HIGH` Browser SFU source, then physically verify exactly one outbound video encoding with progressing publisher/subscriber media. Direct and browser-relay VP8/no-hint performance is already closed by the exact-production gate.
 2. Finish representative ICE/STUN/SFU acceptance, including route recovery, screen-audio continuity and real-game A/V sync on mobile and heterogeneous networks. Browser port prediction, NAT classification, TCP probing, fake page keepalive, and quality-driven reparenting remain outside the accepted model.
 
 ## Active Boundaries

docs/todo.md

@@ -6,7 +6,7 @@ Only items in **Now** are executable after their stated decision gate. A branch
 
 ## Now
 
-1. **Align Browser SFU publication with the accepted single-`HIGH` verdict.** Exact production Chrome 151 closed the intrinsic VP8/no-hint shortfall on direct and browser-relay paths, but proved that the always-active SFU `LOW` materially reduces `HIGH` on the measured public ingress. Replace the current ordered `q,h` publication with one VP8 `HIGH` representation, remove only the now-unowned two-layer helpers and assertions, deploy the exact artifact, and physically verify one outbound video encoding plus progressing publisher/subscriber frames over LiveKit UDP. Do not change direct/browser-relay media, `contentHint`, route ordering, deadlines, or add a bitrate controller.
+1. **Deploy and prove the current single-`HIGH` Browser SFU publication.** Exact production Chrome 151 closed the intrinsic VP8/no-hint shortfall on direct and browser-relay paths, but proved that the always-active SFU `LOW` materially reduces `HIGH` on the measured public ingress. Current source now uses one VP8 `HIGH` encoding and removes only the unowned two-layer helpers and assertions. Deploy the exact artifact and physically verify exactly one outbound video encoding, no RID or second representation, and progressing publisher/subscriber frames over LiveKit UDP. Do not change direct/browser-relay media, `contentHint`, route ordering, deadlines, or add a bitrate controller.
 2. **Finish real-network route acceptance.** Measure standard ICE/STUN direct paths, peer relay, SFU ingress/subscription, exact first-frame commit and rollback, relay-ingress repair with subtree retention, disconnect/capacity drain, Pause/Resume, screen-audio continuity and real-game A/V sync, and bounded explicit failure across representative IPv4/IPv6 NATs and mobile networks. Include an all-UDP-blocked case to establish the current failure boundary. Do not add port prediction, NAT classification, TCP probes, guessed candidates, route scores, or quality-driven reparenting.
 
 ## Accepted Later Roadmap

docs/verification-status.md

@@ -35,11 +35,11 @@ Capacity and routing entries below describe the exact tested source or release o
 ## Open Proof Boundaries
 
 - Routing: exact v10 local direct loopback remains historical evidence for admission-20 initial ingress and exact-candidate first-frame commit timing on that source. Current v12 production still needs route rollback, direct-stage exhaustion and SFU admission, relay-ingress reparent with subtree retention, disconnect/effective-capacity drain, pause/resume, and bounded failure on real browser/media paths. Silent control partitions may wait 30 to 60 seconds for heartbeat detection before the default five-second grace; a non-paused decoded-frame stall may invalidate only that exact child edge.
-- Quality: exact-production direct and Browser-relay VP8/no-hint cadence is closed. The current dual-representation SFU publication failed ADR-0007's quality gate; source/deployment alignment and exact single-representation publisher/subscriber evidence remain open. Startup ramp is stock BWE behavior and does not authorize an SDP or application bitrate workaround.
+- Quality: exact-production direct and Browser-relay VP8/no-hint cadence is closed. Current source implements ADR-0007's single-`HIGH` SFU publication; deployment and exact single-representation publisher/subscriber evidence remain open. Startup ramp is stock BWE behavior and does not authorize an SDP or application bitrate workaround.
 - Host background: deferred until the report reproduces on exact production with a continuously changing real game or replay, a separate direct wired Viewer, synchronized capture/outbound/inbound plus CPU/GPU evidence, and repeated focused/unfocused/hidden/minimized windows. The current-Chrome Browser `getDisplayMedia()` WPF-window screening did not observe an immediate Host-page media drop, and the old harmful `contentHint = "motion"` release remains a plausible confound rather than a proven background cause. Current evidence authorizes no keepalive, Wake Lock, timer, codec switch, route change, or Native fallback.
 - Relay resources: current source and production expose the authenticated `1/2/3` endpoint-cap boundary, and retained v10 local loopback evidence covers 20 Viewers at cap `2` only for that source. CPU/GPU/upload and heterogeneous-network measurements remain diagnostics, not authority to change the contract.
 - Room scale: current source and production admit 20 Viewers plus one Host, and the retained v10 local Browser convergence gate covers that bound on direct loopback. A real public-network 1:20 session, quality, and sustained resource matrix remain open.
-- SFU: production uses one Host publication with exact Viewer subscriptions and no fixed root-count or room-wide lease rule. Browser SFU PCs use the accepted empty-external-ICE-server rule and owner physical media proof closed the reported connection hold. Current production still publishes `q,h`; the accepted single-`HIGH` source/deployment change and its exact physical gate remain open. Real LiveKit lifecycle/JWT replay, resource use, SFU-fed first-child behavior, and broader heterogeneous-network acceptance remain open.
+- SFU: production uses one Host publication with exact Viewer subscriptions and no fixed root-count or room-wide lease rule. Browser SFU PCs use the accepted empty-external-ICE-server rule and owner physical media proof closed the reported connection hold. Current source publishes one `HIGH` encoding without simulcast or a subscriber layer selector, while production still publishes `q,h`; exact deployment and physical proof remain open. Real LiveKit lifecycle/JWT replay, resource use, SFU-fed first-child behavior, and broader heterogeneous-network acceptance remain open.
 - Audio: current v12 source and production select the exact active ordinary Host or SFU publisher audio sender, reset samples across track changes or absence, keep relay children synchronized with persistent-stream audio changes, and reacquire exact SFU publications/senders after reconnect. The reported active-source `1 kbps` observation and all three live ceilings are physically closed on current Chrome/production across direct, browser-relay and SFU. Audible game quality, heterogeneous-network changes and real-game A/V synchronization remain part of route acceptance; a muted/idle Opus track may still legitimately remain near 1 kbps.
 - Observability: current v12 source and production keep local connection details but no Host/Viewer diagnostic downloads or Browser file-export plumbing. The Host-only bounded snapshot stays for automatic acceptance. Chrome 151 supplied selected candidate endpoints and ordinary-route A/V playout timestamps in the current gate, but omitted the SFU A/V timestamp. Target-browser availability and actual values remain open for codec/fmtp and encoder implementation/power efficiency, media-source and encoded FPS, and broader jitter/concealment cases. All retained fields diagnose and have no recovery authority; they do not by themselves prove hardware encode, synchronization quality, or route quality.
 - Mobile: Android/iOS remain Viewer-only. Autoplay, rotation, iOS lock-screen/page reclamation, background reconnection, and network changes need device evidence. AirPlay/system mirroring is Viewer-local output, not a portable in-app WebRTC output contract.

src/client/media/quality.ts

@@ -93,19 +93,12 @@ export interface VideoSenderParameterReadback {
   mismatches: Array<keyof VideoSenderParameterValues>;
 }
 
-export interface TwoLayerVideoSenderParameterReadback {
-  low: VideoSenderParameterReadback;
-  high: VideoSenderParameterReadback;
-}
-
 export interface AudioSenderParameterReadback {
   requestedMaxBitrate: number;
   appliedMaxBitrate: number | null;
   mismatch: boolean;
 }
 
-export const SCREEN_SHARE_LOW_SCALE = 2;
-
 export function resolveScreenAudioQuality(
   quality: ScreenAudioQuality | undefined,
 ): ScreenAudioQuality {
@@ -118,10 +111,6 @@ export function screenAudioBitrate(
   return SCREEN_AUDIO_BITRATES[resolveScreenAudioQuality(quality)];
 }
 
-export function screenShareLowBitrate(profile: QualityProfile): number {
-  return Math.max(150_000, Math.floor(profile.maxBitrate / 4));
-}
-
 export function qualitySettingsEqual(
   left: QualitySettings,
   right: QualitySettings,
@@ -257,9 +246,8 @@ function requestedScaleResolutionDownBy(
 function readVideoSenderParameters(
   parameters: RTCRtpSendParameters,
   includeAppliedScalabilityMode: boolean,
-  encodingIndex = 0,
 ): VideoSenderParameterValues {
-  const encoding = parameters.encodings[encodingIndex];
+  const encoding = parameters.encodings[0];
   const scalabilityMode = (
     encoding as
       | (RTCRtpEncodingParameters & { scalabilityMode?: unknown })
@@ -290,21 +278,6 @@ function senderParameterReadback(
   return { requested, applied, mismatches };
 }
 
-function requiredTwoLayerEncodingIndexes(
-  parameters: RTCRtpSendParameters,
-): { low: number; high: number } {
-  if (parameters.encodings.length !== 2) {
-    throw new Error("SFU simulcast requires exactly two video encodings");
-  }
-  if (
-    parameters.encodings[0]?.rid !== "q" ||
-    parameters.encodings[1]?.rid !== "h"
-  ) {
-    throw new Error("SFU simulcast requires ordered q and h video encodings");
-  }
-  return { low: 0, high: 1 };
-}
-
 function sameParameter(
   key: keyof VideoSenderParameterValues,
   requested: number | string | null,
@@ -376,47 +349,6 @@ export function audioSenderParameterWarning(
     : `浏览器将音频码率上限改写为 ${Math.round(readback.appliedMaxBitrate / 1_000)} kbps`;
 }
 
-export async function configureTwoLayerVideoSender(
-  sender: RTCRtpSender,
-  profile: QualityProfile,
-): Promise<TwoLayerVideoSenderParameterReadback> {
-  const parameters = sender.getParameters();
-  const indexes = requiredTwoLayerEncodingIndexes(parameters);
-  const highScale = requestedScaleResolutionDownBy(sender, profile);
-  const lowEncoding = parameters.encodings[indexes.low]!;
-  const highEncoding = parameters.encodings[indexes.high]!;
-
-  lowEncoding.maxBitrate = screenShareLowBitrate(profile);
-  lowEncoding.maxFramerate = profile.maxFramerate;
-  lowEncoding.scaleResolutionDownBy = highScale * SCREEN_SHARE_LOW_SCALE;
-  highEncoding.maxBitrate = profile.maxBitrate;
-  highEncoding.maxFramerate = profile.maxFramerate;
-  highEncoding.scaleResolutionDownBy = highScale;
-  parameters.degradationPreference = profile.degradationPreference;
-
-  const requestedLow = readVideoSenderParameters(parameters, false, indexes.low);
-  const requestedHigh = readVideoSenderParameters(parameters, false, indexes.high);
-  await sender.setParameters(parameters);
-
-  const appliedParameters = sender.getParameters();
-  const appliedIndexes = requiredTwoLayerEncodingIndexes(appliedParameters);
-  const appliedLow = readVideoSenderParameters(
-    appliedParameters,
-    false,
-    appliedIndexes.low,
-  );
-  const appliedHigh = readVideoSenderParameters(
-    appliedParameters,
-    false,
-    appliedIndexes.high,
-  );
-
-  return {
-    low: senderParameterReadback(requestedLow, appliedLow),
-    high: senderParameterReadback(requestedHigh, appliedHigh),
-  };
-}
-
 const PARAMETER_LABELS = {
   maxBitrate: "码率上限",
   maxFramerate: "帧率上限",

src/client/sfu/publisher.ts

@@ -8,13 +8,10 @@ import type {
 import {
   audioSenderParameterWarning,
   configureScreenAudioSender,
-  configureTwoLayerVideoSender,
-  QUALITY_RESOLUTIONS,
+  configureVideoSender,
   resolveScreenAudioQuality,
   screenAudioQualityEqual,
-  SCREEN_SHARE_LOW_SCALE,
   screenAudioBitrate,
-  screenShareLowBitrate,
   senderParameterWarning,
   videoQualitySettingsEqual,
   type AudioSenderParameterReadback,
@@ -191,7 +188,7 @@ export class SfuPublisher {
           room,
           videoTrack,
           sdk.Track.Source.ScreenShare,
-          videoPublishOptions(sdk, profile),
+          videoPublishOptions(profile),
         );
         if (!this.owns(room, generation)) {
           return false;
@@ -200,7 +197,6 @@ export class SfuPublisher {
         const videoConfiguration = await configurePublishedVideo(
           video,
           profile,
-          sdk,
           () => this.owns(room, generation),
         );
         if (!videoConfiguration || !this.owns(room, generation)) {
@@ -396,7 +392,6 @@ export class SfuPublisher {
         const videoConfiguration = await configurePublishedVideo(
           previousVideo,
           profile,
-          sdk,
           () => this.owns(room, generation),
         );
         if (!videoConfiguration || !this.owns(room, generation)) {
@@ -450,7 +445,6 @@ export class SfuPublisher {
             const videoConfiguration = await configurePublishedVideo(
               previousVideo,
               previousVideoProfile,
-              sdk,
               () => this.owns(room, generation),
             );
             if (!videoConfiguration || !this.owns(room, generation)) {
@@ -537,7 +531,6 @@ export class SfuPublisher {
           const configured = await configurePublishedVideo(
             video,
             profile,
-            sdk,
             () =>
               this.owns(room, generation) &&
               requestedRevision === this.profileRevision &&
@@ -569,7 +562,6 @@ export class SfuPublisher {
             const rolledBack = await configurePublishedVideo(
               video,
               previousVideoProfile,
-              sdk,
               () =>
                 this.owns(room, generation) &&
                 requestedRevision === this.profileRevision &&
@@ -1018,7 +1010,6 @@ export class SfuPublisher {
           identity.accumulator,
           {
             trackIdentifier: identity.videoTrack.id,
-            rid: "h",
             audioTrackIdentifier: identity.audioTrack?.id ?? null,
           },
         ),
@@ -1091,7 +1082,6 @@ async function unpublishTrack(room: Room, published: PublishedTrack): Promise<vo
 async function configurePublishedVideo(
   published: PublishedTrack,
   profile: QualityProfile,
-  sdk: LiveKit,
   ownsPublication: () => boolean,
 ): Promise<PublishedVideoConfiguration | null> {
   const videoTrack = published.publication.videoTrack;
@@ -1107,7 +1097,7 @@ async function configurePublishedVideo(
     }
     return null;
   }
-  const readbacks = await configureTwoLayerVideoSender(sender, profile);
+  const readback = await configureVideoSender(sender, profile);
   if (!ownsPublication()) {
     if (previousPreference) {
       await videoTrack.setDegradationPreference(previousPreference);
@@ -1117,18 +1107,13 @@ async function configurePublishedVideo(
   const retainedPublishOptions = {
     ...published.publication.options,
     ...videoTrack.publishOptions,
-    ...videoPublishOptions(sdk, profile),
+    ...videoPublishOptions(profile),
   };
   published.publication.options = retainedPublishOptions;
   videoTrack.publishOptions = retainedPublishOptions;
-  const highWarning = senderParameterWarning(readbacks.high);
-  const lowWarning = senderParameterWarning(readbacks.low);
   return {
-    readback: readbacks.high,
-    warning: mergeQualityWarnings(
-      highWarning,
-      lowWarning ? `低档表示：${lowWarning}` : null,
-    ),
+    readback,
+    warning: senderParameterWarning(readback),
   };
 }
 
@@ -1205,27 +1190,15 @@ function mergeQualityWarnings(...warnings: Array<string | null>): string | null
   return present.length > 0 ? present.join("；") : null;
 }
 
-function videoPublishOptions(
-  sdk: LiveKit,
-  profile: QualityProfile,
-): TrackPublishOptions {
-  const highResolution = QUALITY_RESOLUTIONS[profile.resolution];
+function videoPublishOptions(profile: QualityProfile): TrackPublishOptions {
   return {
     backupCodec: false,
     videoCodec: "vp8",
-    simulcast: true,
+    simulcast: false,
     screenShareEncoding: {
       maxBitrate: profile.maxBitrate,
       maxFramerate: profile.maxFramerate,
     },
-    screenShareSimulcastLayers: [
-      new sdk.VideoPreset(
-        Math.floor(highResolution.width / SCREEN_SHARE_LOW_SCALE),
-        Math.floor(highResolution.height / SCREEN_SHARE_LOW_SCALE),
-        screenShareLowBitrate(profile),
-        profile.maxFramerate,
-      ),
-    ],
     degradationPreference: profile.degradationPreference,
   };
 }

src/client/sfu/subscriber.ts

@@ -313,11 +313,6 @@ export class SfuSubscriber {
     }
     this.desiredTrackSids.add(publication.trackSid);
     publication.setSubscribed(true);
-    if (publication.source === sdk.Track.Source.ScreenShare) {
-      // HIGH is a ceiling. LiveKit's per-subscriber BWE may still forward LOW
-      // while this path is constrained and return to HIGH after recovery.
-      publication.setVideoQuality(sdk.VideoQuality.HIGH);
-    }
   }
 
   private rememberHostParticipant(

tests/quality.test.ts

@@ -5,14 +5,12 @@ import {
   applyCaptureProfile,
   captureDisplay,
   configureScreenAudioSender,
-  configureTwoLayerVideoSender,
   configureVideoSender,
   matchingQualityProfileId,
   QUALITY_PROFILES,
   QUALITY_RESOLUTIONS,
   qualitySettingsEqual,
   SCREEN_AUDIO_BITRATES,
-  screenShareLowBitrate,
   senderParameterWarning,
   setMediaPaused,
 } from "../src/client/media/quality.ts";
@@ -353,93 +351,6 @@ describe("realtime quality controls", () => {
     expect(readback.mismatches).not.toContain("scalabilityMode");
   });
 
-  it("configures ordered LOW and HIGH simulcast encodings without flattening LOW", async () => {
-    let applied = {
-      encodings: [{ rid: "q" }, { rid: "h" }],
-    } as RTCRtpSendParameters;
-    const sender = {
-      track: {
-        getSettings: () => ({ width: 2560, height: 1440 }),
-      },
-      getParameters: () => applied,
-      setParameters: vi.fn(async (parameters: RTCRtpSendParameters) => {
-        applied = parameters;
-      }),
-    } as unknown as RTCRtpSender;
-
-    const readbacks = await configureTwoLayerVideoSender(
-      sender,
-      QUALITY_PROFILES["1080p60"],
-    );
-
-    expect(applied).toMatchObject({
-      degradationPreference: "balanced",
-      encodings: [
-        {
-          rid: "q",
-          maxBitrate: 2_000_000,
-          maxFramerate: 60,
-          scaleResolutionDownBy: 8 / 3,
-        },
-        {
-          rid: "h",
-          maxBitrate: 8_000_000,
-          maxFramerate: 60,
-          scaleResolutionDownBy: 4 / 3,
-        },
-      ],
-    });
-    expect(readbacks.low.requested.maxBitrate).toBe(2_000_000);
-    expect(readbacks.high.requested.maxBitrate).toBe(8_000_000);
-    expect(readbacks.low.mismatches).toEqual([]);
-    expect(readbacks.high.mismatches).toEqual([]);
-  });
-
-  it("keeps the standard LOW bitrate floor for small custom HIGH ceilings", () => {
-    expect(
-      screenShareLowBitrate({
-        resolution: "720p",
-        maxFramerate: 30,
-        maxBitrate: 400_000,
-        degradationPreference: "balanced",
-      }),
-    ).toBe(150_000);
-  });
-
-  it.each([
-    {
-      label: "drops HIGH",
-      after: { encodings: [{ rid: "q" }] },
-      message: "exactly two video encodings",
-    },
-    {
-      label: "reorders the RIDs",
-      after: { encodings: [{ rid: "h" }, { rid: "q" }] },
-      message: "ordered q and h video encodings",
-    },
-    {
-      label: "adds a third RID",
-      after: { encodings: [{ rid: "q" }, { rid: "h" }, { rid: "f" }] },
-      message: "exactly two video encodings",
-    },
-  ])("fails closed when sender readback $label", async ({ after, message }) => {
-    const before = {
-      encodings: [{ rid: "q" }, { rid: "h" }],
-    } as RTCRtpSendParameters;
-    const sender = {
-      track: { getSettings: () => ({ width: 1920, height: 1080 }) },
-      getParameters: vi
-        .fn<() => RTCRtpSendParameters>()
-        .mockReturnValueOnce(before)
-        .mockReturnValue(after as RTCRtpSendParameters),
-      setParameters: vi.fn(async () => undefined),
-    } as unknown as RTCRtpSender;
-
-    await expect(
-      configureTwoLayerVideoSender(sender, QUALITY_PROFILES["1080p60"]),
-    ).rejects.toThrow(message);
-  });
-
   it("pauses and resumes the shared video and audio tracks together", () => {
     const { stream, videoTrack, audioTrack } = createVideoStream();
 

tests/sfu-client.test.ts

@@ -8,30 +8,6 @@ import { mergeStatsReports } from "../src/client/webrtc/stats.ts";
 type EventHandler = (...args: unknown[]) => void;
 
 const livekit = vi.hoisted(() => {
-  class FakeVideoPreset {
-    readonly encoding: {
-      maxBitrate: number;
-      maxFramerate?: number;
-    };
-
-    constructor(
-      readonly width: number,
-      readonly height: number,
-      maxBitrate: number,
-      maxFramerate?: number,
-    ) {
-      this.encoding = { maxBitrate, maxFramerate };
-    }
-
-    get resolution(): { width: number; height: number; frameRate?: number } {
-      return {
-        width: this.width,
-        height: this.height,
-        frameRate: this.encoding.maxFramerate,
-      };
-    }
-  }
-
   class FakeSender {
     track: MediaStreamTrack;
     failNextSetParameters = false;
@@ -131,32 +107,21 @@ const livekit = vi.hoisted(() => {
       ) => {
         const localTrack = new FakeLocalTrack(rawTrack);
         localTrack.publishOptions = options;
-        const simulcastLayers = options.screenShareSimulcastLayers;
-        const highEncoding = options.screenShareEncoding;
+        const screenShareEncoding = options.screenShareEncoding;
         if (
           rawTrack.kind === "video" &&
-          options.simulcast === true &&
-          Array.isArray(simulcastLayers) &&
-          simulcastLayers.length === 1 &&
-          simulcastLayers[0] instanceof FakeVideoPreset &&
-          typeof highEncoding === "object" &&
-          highEncoding !== null
+          options.simulcast === false &&
+          typeof screenShareEncoding === "object" &&
+          screenShareEncoding !== null
         ) {
-          const high = highEncoding as {
+          const encoding = screenShareEncoding as {
             maxBitrate?: number;
             maxFramerate?: number;
           };
           localTrack.sender.parameters.encodings = [
             {
-              rid: "q",
-              maxBitrate: simulcastLayers[0].encoding.maxBitrate,
-              maxFramerate: simulcastLayers[0].encoding.maxFramerate,
-              scaleResolutionDownBy: 2,
-            },
-            {
-              rid: "h",
-              maxBitrate: high.maxBitrate,
-              maxFramerate: high.maxFramerate,
+              maxBitrate: encoding.maxBitrate,
+              maxFramerate: encoding.maxFramerate,
               scaleResolutionDownBy: 1,
             },
           ];
@@ -205,15 +170,9 @@ const livekit = vi.hoisted(() => {
 
   class FakeRemotePublication {
     subscribed = false;
-    requestedVideoQuality: string | null = null;
     readonly setSubscribed = vi.fn((subscribed: boolean) => {
       this.subscribed = subscribed;
     });
-    readonly setVideoQuality = vi.fn((quality: string) => {
-      if (this.subscribed) {
-        this.requestedVideoQuality = quality;
-      }
-    });
 
     constructor(
       readonly trackSid: string,
@@ -285,7 +244,6 @@ const livekit = vi.hoisted(() => {
     FakeRemoteParticipant,
     FakeRemotePublication,
     FakeRoom,
-    FakeVideoPreset,
     state,
   };
 });
@@ -310,17 +268,11 @@ const Track = {
   },
 } as const;
 
-const VideoQuality = {
-  HIGH: "high",
-} as const;
-
 vi.mock("livekit-client", () => ({
   AudioPresets: livekit.AudioPresets,
   Room: livekit.FakeRoom,
   RoomEvent,
   Track,
-  VideoPreset: livekit.FakeVideoPreset,
-  VideoQuality,
 }));
 
 class FakeMediaStream {
@@ -407,27 +359,11 @@ function senderReport(
   framesEncoded: number,
 ): RTCStatsReport {
   return statsReport([
-    {
-      id: "video-out-low",
-      type: "outbound-rtp",
-      timestamp,
-      kind: "video",
-      rid: "q",
-      mediaSourceId: "video-source",
-      bytesSent: Math.floor(bytesSent / 4),
-      framesEncoded: Math.floor(framesEncoded / 4),
-      framesPerSecond: 15,
-      frameWidth: 960,
-      frameHeight: 540,
-      totalEncodeTime: framesEncoded * 0.002,
-      qualityLimitationReason: "none",
-    },
     {
       id: "video-out",
       type: "outbound-rtp",
       timestamp,
       kind: "video",
-      rid: "h",
       transportId: "transport",
       codecId: "codec",
       mediaSourceId: "video-source",
@@ -558,7 +494,7 @@ describe("SfuPublisher", () => {
       captureHeight: 1080,
       captureFramesPerSecond: 60,
       trackIdentifier: previousVideo.id,
-      rtpRid: "h",
+      rtpRid: null,
       mediaSourceFramesPerSecond: 59,
       framesPerSecond: 57,
       resolution: "1920x1080",
@@ -699,7 +635,7 @@ describe("SfuPublisher", () => {
     expect(livekit.state.rooms[0]?.disconnect).toHaveBeenCalledWith(false);
   });
 
-  it("publishes exactly the ordered q and h video encodings", async () => {
+  it("publishes exactly one VP8 video encoding", async () => {
     const publisher = new SfuPublisher();
     const video = track("video", "video-1");
     const audio = track("audio", "audio-1");
@@ -715,21 +651,11 @@ describe("SfuPublisher", () => {
       source: Track.Source.ScreenShare,
       backupCodec: false,
       videoCodec: "vp8",
-      simulcast: true,
+      simulcast: false,
       screenShareEncoding: {
         maxBitrate: 8_000_000,
         maxFramerate: 60,
       },
-      screenShareSimulcastLayers: [
-        expect.objectContaining({
-          width: 960,
-          height: 540,
-          encoding: {
-            maxBitrate: 2_000_000,
-            maxFramerate: 60,
-          },
-        }),
-      ],
       degradationPreference: "maintain-resolution",
     });
     expect(
@@ -743,22 +669,13 @@ describe("SfuPublisher", () => {
     });
     expect(sender.setParameters).toHaveBeenCalledOnce();
     expect(sender.parameters.encodings).toEqual([
-      expect.objectContaining({
-        rid: "q",
-        maxBitrate: 2_000_000,
-        maxFramerate: 60,
-        scaleResolutionDownBy: 2,
-      }),
-      expect.objectContaining({
-        rid: "h",
+      {
         maxBitrate: 8_000_000,
         maxFramerate: 60,
         scaleResolutionDownBy: 1,
-      }),
+      },
     ]);
-    expect(
-      sender.parameters.encodings.every((encoding) => encoding.active !== false),
-    ).toBe(true);
+    expect(sender.parameters.encodings[0]).not.toHaveProperty("rid");
     expect(publisher.getSenderParameters()).toEqual({
       requested: {
         maxBitrate: 8_000_000,
@@ -858,13 +775,6 @@ describe("SfuPublisher", () => {
         degradationPreference: "balanced",
         encodings: [
           expect.objectContaining({
-            rid: "q",
-            maxBitrate: 750_000,
-            maxFramerate: 30,
-            scaleResolutionDownBy: 2,
-          }),
-          expect.objectContaining({
-            rid: "h",
             maxBitrate: 3_000_000,
             maxFramerate: 30,
             scaleResolutionDownBy: 1,
@@ -1184,13 +1094,6 @@ describe("SfuPublisher", () => {
       degradationPreference: "maintain-framerate",
       encodings: [
         {
-          rid: "q",
-          maxBitrate: 750_000,
-          maxFramerate: 30,
-          scaleResolutionDownBy: 2,
-        },
-        {
-          rid: "h",
           maxBitrate: 3_000_000,
           maxFramerate: 30,
           scaleResolutionDownBy: 1,
@@ -1328,41 +1231,6 @@ describe("SfuPublisher", () => {
     expect(publisher.getQualityWarning()).toContain("码率上限");
   });
 
-  it("reports a LOW rewrite while retaining HIGH sender readback", async () => {
-    const publisher = new SfuPublisher();
-    await publisher.connect(connection);
-    await publisher.activate(stream(track("video", "video-1")), qualityProfile);
-    const sender = livekit.state.rooms[0].localParticipant.publications[0].track
-      .sender;
-    sender.setParameters.mockImplementationOnce(async (parameters) => {
-      sender.parameters = {
-        ...parameters,
-        encodings: parameters.encodings.map((encoding, index) =>
-          index === 0
-            ? { ...encoding, maxBitrate: 200_000 }
-            : { ...encoding },
-        ),
-      };
-    });
-
-    await expect(
-      publisher.updateProfile({
-        resolution: "1080p",
-        maxFramerate: 30,
-        maxBitrate: 5_000_000,
-        degradationPreference: "balanced",
-      }),
-    ).resolves.toBe(true);
-
-    expect(publisher.getSenderParameters()).toMatchObject({
-      requested: { maxBitrate: 5_000_000 },
-      applied: { maxBitrate: 5_000_000 },
-      mismatches: [],
-    });
-    expect(publisher.getQualityWarning()).toContain("低档表示");
-    expect(publisher.getQualityWarning()).toContain("码率上限");
-  });
-
   it("retains a visible warning when SFU sender parameters are rejected", async () => {
     const publisher = new SfuPublisher();
     await publisher.connect(connection);
@@ -1396,12 +1264,6 @@ describe("SfuPublisher", () => {
       degradationPreference: "maintain-resolution",
       encodings: [
         expect.objectContaining({
-          rid: "q",
-          maxBitrate: 2_000_000,
-          maxFramerate: 60,
-        }),
-        expect.objectContaining({
-          rid: "h",
           maxBitrate: 8_000_000,
           maxFramerate: 60,
         }),
@@ -1411,7 +1273,7 @@ describe("SfuPublisher", () => {
     expect(publisher.getQualityWarning()).not.toContain("unsupported");
   });
 
-  it("retains a LOW rewrite warning after rolling back sender parameters", async () => {
+  it("retains a sender rewrite warning after rolling back parameters", async () => {
     const publisher = new SfuPublisher();
     await publisher.connect(connection);
     await publisher.activate(stream(track("video", "video-1")), qualityProfile);
@@ -1422,11 +1284,10 @@ describe("SfuPublisher", () => {
       .mockImplementationOnce(async (parameters) => {
         sender.parameters = {
           ...parameters,
-          encodings: parameters.encodings.map((encoding, index) =>
-            index === 0
-              ? { ...encoding, maxBitrate: 1_500_000 }
-              : { ...encoding },
-          ),
+          encodings: parameters.encodings.map((encoding) => ({
+            ...encoding,
+            maxBitrate: 1_500_000,
+          })),
         };
       });
 
@@ -1441,12 +1302,11 @@ describe("SfuPublisher", () => {
 
     expect(publisher.getSenderParameters()).toMatchObject({
       requested: { maxBitrate: 8_000_000 },
-      applied: { maxBitrate: 8_000_000 },
-      mismatches: [],
+      applied: { maxBitrate: 1_500_000 },
+      mismatches: ["maxBitrate"],
     });
     expect(publisher.getQualityWarning()).toContain("应用 SFU 发送参数失败");
     expect(publisher.getQualityWarning()).not.toContain("unsupported");
-    expect(publisher.getQualityWarning()).toContain("低档表示");
     expect(publisher.getQualityWarning()).toContain("码率上限");
   });
 
@@ -1648,7 +1508,6 @@ describe("SfuSubscriber", () => {
 
     expect(subscriber.activate()).toBe(true);
     expect(hostVideo.setSubscribed).toHaveBeenCalledWith(true);
-    expect(hostVideo.setVideoQuality).toHaveBeenCalledWith(VideoQuality.HIGH);
   });
 
   it("reconciles a Host participant that appears after activation", async () => {
@@ -1666,10 +1525,9 @@ describe("SfuSubscriber", () => {
     room.emit(RoomEvent.ParticipantConnected, host);
 
     expect(hostVideo.setSubscribed).toHaveBeenCalledWith(true);
-    expect(hostVideo.setVideoQuality).toHaveBeenCalledWith(VideoQuality.HIGH);
   });
 
-  it("keeps the assigned screen subscription at a HIGH ceiling", async () => {
+  it("subscribes only to assigned Host screen tracks", async () => {
     const gate = deferred();
     livekit.state.connectGate = gate.promise;
     const streams: Array<MediaStream | null> = [];
@@ -1711,19 +1569,9 @@ describe("SfuSubscriber", () => {
     expect(hostVideo.setSubscribed).not.toHaveBeenCalled();
     expect(streams).toEqual([]);
 
-    hostVideo.setVideoQuality(VideoQuality.HIGH);
-    expect(hostVideo.requestedVideoQuality).toBeNull();
-    hostVideo.setVideoQuality.mockClear();
-
     expect(subscriber.activate()).toBe(true);
     expect(hostVideo.setSubscribed).toHaveBeenCalledWith(true);
     expect(hostAudio.setSubscribed).toHaveBeenCalledWith(true);
-    expect(hostVideo.setVideoQuality).toHaveBeenCalledWith(VideoQuality.HIGH);
-    expect(hostVideo.requestedVideoQuality).toBe(VideoQuality.HIGH);
-    expect(hostVideo.setSubscribed.mock.invocationCallOrder[0]).toBeLessThan(
-      hostVideo.setVideoQuality.mock.invocationCallOrder[0]!,
-    );
-    expect(hostAudio.setVideoQuality).not.toHaveBeenCalled();
     expect(hostCamera.setSubscribed).not.toHaveBeenCalled();
     expect(viewerScreen.setSubscribed).not.toHaveBeenCalled();