Bug 299853 – REGRESSION (Safari 26): Live HLS ID3 timed metadata cues mapped with endTime = Infinity cause TextTrack.activeCues to include all past cues indefinitely

• Component: Media
• Status: RESOLVED FIXED

**Product/Component**

* Product: WebKit
* Component: Media → TextTracks / Timed Metadata
* Version/Build: Safari 26.0 (20622.1.22), 26.0.1 on macOS 26 / iOS 26

**Summary**
Since Safari 26, ID3 timed metadata (in-band HLS) seems to be mapped to `DataCue` objects whose `endTime` is `Infinity`. As a result, `textTrack.activeCues` no longer represents “cues overlapping the current time” but **keeps all cues inserted so far**.
Our ad logic reads the latest **NMSS timestamp** (`info = "com.timestamp"`) from `activeCues`. On Safari 26, `activeCues[0]` sticks to the very first cue, so the parsed `current-utc` value **never updates**. Earlier Safari versions and other browsers behave as expected.

**Context / Potential cause**

* Safari 26 release notes mention *“Added support for in-band tracks in MSE.”* Our path does not use MSE, but there may have been broader changes in TextTrack/timed-metadata plumbing. ([Apple Developer][1])
* The HTML spec defines **unbounded cues** as those with `endTime = +Infinity`, which **cannot become inactive** during normal playback. Safari 26 appears to map ID3 cues as unbounded now. ([html.spec.whatwg.org][2])
* Past discussions proposed using `Infinity` to represent end-of-media, and the Media Timed Events TF discussed **bounding the previous unbounded cue when a new event arrives** to keep a meaningful active set. Safari 26 seems to keep **all** previous ID3 cues unbounded. ([GitHub][3])

**Actual Results**

* `textTrack.activeCues` permanently includes **all NMSS timestamp cues since insertion** → `activeCues[0]` holds a stale `current-utc`
* Mid-roll ad polling logic stops (no “latest timestamp” detected), so no subsequent ad requests fire

**Expected Results**

* Either keep `activeCues` limited to cues that overlap the current playback time (as before), **or**
* If adopting unbounded cues, **bound the previous cue’s `endTime` when a new event arrives**, so the active set remains meaningful around “now”

**Workaround (production-safe)**
On Safari 26, avoid `activeCues` and **search by `startTime` around the current time** (binary search for performance):

```ts
function isSafari26() {
  const ua = navigator.userAgent;
  const isSafari = !!ua.match(/Version\/[\d.]+.*Safari/) && navigator.vendor === 'Apple Computer, Inc.';
  if (!isSafari) return false;
  const m = ua.match(/Version\/(\d+)/);
  return m && parseInt(m[1], 10) === 26;
}

function getNmssTimestampCue(player: HTMLVideoElement, tolerance: number): DataCue | null {
  for (const track of Array.from(player.textTracks)) {
    if (track.kind !== 'metadata') continue;
    if (!track.cues) { if (track.mode === 'disabled') track.mode = 'hidden'; continue; }

    let hasNmss = false;
    for (let i = 0; i < track.cues.length; i++) {
      const { value } = track.cues[i] as any;
      if (value && value.info === 'com.timestamp') { hasNmss = true; break; }
    }
    if (!hasNmss) continue;

    const active = isSafari26() ? getAdjacentCues(track, player.currentTime, tolerance)
                                : (track.activeCues ? Array.from(track.activeCues) : []);
    if (active.length === 0) continue;
    return active[0] as DataCue;
  }
  return null;
}

function getAdjacentCues(track: TextTrack, currentTime: number, tolerance: number): TextTrackCue[] {
  const result: TextTrackCue[] = [];
  const cues = track.cues;
  if (!cues || cues.length === 0) return result;

  let l = 0, r = cues.length - 1, last = -1;
  while (l <= r) {
    const mid = (l + r) >> 1;
    if (cues[mid].startTime <= currentTime) { last = mid; l = mid + 1; }
    else { r = mid - 1; }
  }
  if (last === -1) return result;

  for (let i = last; i >= 0; i--) {
    const cue = cues[i];
    if (currentTime - cue.startTime > tolerance) break;
    result.unshift(cue);
  }
  return result;
}
```

**Regression?**

* Yes. Works on earlier Safari and other engines; breaks on Safari 26.0/26.0.1 (macOS/iOS).

**Questions / Requests**

1. Was mapping ID3 cues to **unbounded** (`endTime = Infinity`) an intentional change in Safari 26?
2. If intentional, could WebKit consider **bounding the previous unbounded cue** when a new event arrives (per MTE TF discussions), or provide guidance on how to fetch the *latest* metadata event without scanning? ([W3C][4])
3. If this is expected by spec, please update release notes/docs to call out the web-compat impact for apps that rely on `activeCues` semantics. Current public notes don’t mention this detail. ([Apple Developer][1])

**References**

* Safari 26 Release Notes (26.0 / 20622.1.22; 26.1 beta list) ([Apple Developer][1])
* WebKit Features in Safari 26.0 (in-band tracks in MSE) ([WebKit][5])
* HTML Standard: unbounded text track cue (`endTime = +Infinity`) & “cannot become inactive” ([html.spec.whatwg.org][2])
* WHATWG: proposal to use `Infinity` for end-of-media ([GitHub][3])
* W3C Media Timed Events TF minutes: bounding previous unbounded cue when a new event arrives ([W3C][4])
* Apple HLS docs (timed metadata overview) ([Apple Developer][6])

---

[1]: https://developer.apple.com/documentation/safari-release-notes
[2]: https://html.spec.whatwg.org/dev/media.html
[3]: https://github.com/whatwg/html/issues/5297
[4]: https://www.w3.org/2021/04/19-me-minutes.html"
[5]: https://webkit.org/blog/17333/webkit-features-in-safari-26-0
[6]: https://developer.apple.com/documentation/http-live-streaming/links-to-additional-specifications-and-videos
[7]: https://docs.aws.amazon.com/medialive/latest/ug/insert-timed-metadata.html

# Reproduction Steps

Test on Safari 26.0 or 26.0.1 (macOS 26 / iOS 26)

Open Developer Tools (Inspector) → Console tab

Run the following snippet:

const video = document.querySelector('video');
for (const track of video.textTracks) {
  if (track.kind === 'metadata') {
    track.mode = 'hidden'; // ensure cues are exposed
    console.log('metadata track:', track);
    console.log('activeCues:', Array.from(track.activeCues || []));
  }
}

- On Safari 26, track.activeCues does not include only the latest cue, but instead retains all past NMSS timestamp cues
- On Safari 25 or earlier, and on Chrome/Firefox, activeCues correctly returns only the cues that overlap the current playback position

[Radar WebKit Bug Importer]

<rdar://problem/161687917>

issue can be reproduced on https://chzzk.naver.com/
while some streams are region-locked, most can be played.

reproduced on iOS 18 and later, macOS Sequoia, and macOS Tahoe.
Similar to bug 255499.

[Eric Carlson]

Pull request: https://github.com/WebKit/WebKit/pull/53144

[EWS]

Committed 302395@main (01952a527b50): <https://commits.webkit.org/302395@main>

Reviewed commits have been landed. Closing PR #53144 and removing active labels.