52 lines
2.3 KiB
Markdown
52 lines
2.3 KiB
Markdown
# ECP-0090: PAT-Derived Broadcast Identity Promotion
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Status: Implemented
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## Decision
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Extend default discovery identity synthesis to probe early MPEG-TS packets for Program Association Table (PAT) data and use that to strengthen broadcast-scoped stream IDs.
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Current rule:
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- If source/channel metadata already yields a usable broadcast identity, use it.
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- If transport probing finds PAT data, fill missing `transport_stream_id` and `program_number`.
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- If PAT shows exactly one non-zero program, that program is eligible for broadcast-scoped convergence.
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- If PAT is ambiguous (multiple non-zero programs), do not guess; keep `program_number` unset and fall back to source scope when needed.
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- If the probe sees ATSC PSIP traffic, label the standard as `atsc`; otherwise use a generic `mpegts` fallback when PAT is the only signal.
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## Motivation
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ECP-0089 fixed the first duplication bug by preferring channel metadata over source-local IDs. That still left a hole:
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- raw TS sources without lineup metadata could not converge,
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- channel metadata could be incomplete or inconsistent,
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- and weak identity inputs risked accidental convergence on the wrong broadcast.
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PAT-derived identity gives us a stronger on-wire fingerprint without waiting for full PSIP/VCT parsing.
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## Scope
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In scope:
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- PAT parsing in `ec-ts`
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- bounded transport probing for `tsid` / single-program extraction
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- source integration for raw TS inputs and HDHomeRun enrichment
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- tests that enforce "single program promotes, ambiguous stream does not"
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Out of scope:
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- full ATSC VCT/MGT descriptor parsing
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- DVB service table parsing
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- cryptographic origin authentication for discovery announcements
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## Alternatives considered
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- Keep trusting channel metadata only. Rejected because it leaves raw TS paths weak and incomplete.
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- Always promote from PAT even with multiple programs. Rejected because it guesses the channel and increases junk-collision risk.
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- Require manual `--stream-id` for TS inputs. Rejected because it pushes canonicalization burden onto operators.
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## Rollout / Reversibility
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- Additive and reversible: explicit `--stream-id` still overrides everything.
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- Roll back by removing PAT probing and returning to metadata-only promotion.
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- Future PSIP/VCT work can refine the broadcast identity without changing the override surface.
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