every.channel/evolution/proposals/ECP-0090-pat-derived-broadcast-identity.md

ECP-0090: PAT-Derived Broadcast Identity Promotion

Status: Implemented

Decision

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.

Current rule:

• If source/channel metadata already yields a usable broadcast identity, use it.
• If transport probing finds PAT data, fill missing transport_stream_id and program_number.
• If PAT shows exactly one non-zero program, that program is eligible for broadcast-scoped convergence.
• If PAT is ambiguous (multiple non-zero programs), do not guess; keep program_number unset and fall back to source scope when needed.
• If the probe sees ATSC PSIP traffic, label the standard as atsc; otherwise use a generic mpegts fallback when PAT is the only signal.

Motivation

ECP-0089 fixed the first duplication bug by preferring channel metadata over source-local IDs. That still left a hole:

• raw TS sources without lineup metadata could not converge,
• channel metadata could be incomplete or inconsistent,
• and weak identity inputs risked accidental convergence on the wrong broadcast.

PAT-derived identity gives us a stronger on-wire fingerprint without waiting for full PSIP/VCT parsing.

Scope

In scope:

• PAT parsing in ec-ts
• bounded transport probing for tsid / single-program extraction
• source integration for raw TS inputs and HDHomeRun enrichment
• tests that enforce "single program promotes, ambiguous stream does not"

Out of scope:

• full ATSC VCT/MGT descriptor parsing
• DVB service table parsing
• cryptographic origin authentication for discovery announcements

Alternatives considered

• Keep trusting channel metadata only. Rejected because it leaves raw TS paths weak and incomplete.
• Always promote from PAT even with multiple programs. Rejected because it guesses the channel and increases junk-collision risk.
• Require manual --stream-id for TS inputs. Rejected because it pushes canonicalization burden onto operators.

Rollout / Reversibility

• Additive and reversible: explicit --stream-id still overrides everything.
• Roll back by removing PAT probing and returning to metadata-only promotion.
• Future PSIP/VCT work can refine the broadcast identity without changing the override surface.