| name | browser-playback-align |
| description | Align a browser media playback session with a local worker, runtime, or decrypt/remux pipeline. Use when debugging playback mismatches between browser and local runs, reproducing worker state locally from a page URL or playlist, comparing `vmpTag`-like state sequences, tracing zero-length decrypt outputs, mapping browser worker calls back to raw media units, or replaying browser-to-worker message order offline. |
Browser Playback Align
Use this skill when a browser player works one way and a local reproduction works another way.
Core Workflow
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Identify the real browser session.
Capture the target page URL, actual worker URL, actual session/media ID, actual playlist/segment URLs, and the browser worker state sequence.
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Reproduce with the worker path first.
Prefer the actual browser worker or worker-harness path over calling a lower-level runtime directly. Lower-level runtime calls are useful for reduction, but they often miss session state.
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Map zero-output calls back to raw media units.
Search worker logs for zero-length outputs, then map them to segment index, call ordinal, media unit type, timing, and raw input bytes.
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Compare state lines, not just inputs.
When the same media unit behaves differently, compare the browser and local state sequence at the same ordinal. A matching input with a different state line is a different experiment.
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Replay browser message order locally.
Capture the actual main-worker postMessage sequence from the browser. Replaying just the final media segments is often not enough.
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Reduce the divergence window.
Once you locate a problematic call, compare its neighboring ordinals, try alternate timing tags, and skip earlier ordinals to find which earlier inputs build the later state line.
Operating Rules
- Treat the browser main worker as authoritative for state sequencing.
- Ignore audio-worker state when the bug is in the main video/decrypt path.
- Do not assume the worker state is a pure function of one media unit. Earlier control messages and prior media units can matter.
- Do not assume matching page URL, time, and worker URL are sufficient. They help, but they do not guarantee a matching state line.
- Keep browser capture artifacts and local replay artifacts side by side so each claim can be traced to a file.
Typical Questions This Skill Should Answer
- Which earlier browser call first pushed the worker into the problematic state line?
- Does zero-length output happen only in the browser, only locally, or in both?
- Is the problem tied to one timing tag, one media unit family, or one state transition?
- Does skipping or replaying an earlier ordinal change the later failure?
- Does replaying the browser main-worker message order make the local state sequence converge?
Reference File
