docs(millicast): document enableUTCInsertion publishing parameter

[bcostdolby]

Summary

Documents the new enableUTCInsertion ingest option (media-server OPTI-3526) in the public Millicast docs. The feature stamps H.264 media with an unregistered SEI carrying the server's UTC receive time (Unix epoch ms), for RTMP/SRT passthrough and transcoded H.264 layers, without re-encoding, and only when the ingest doesn't already provide an onFi/AMF sender time.

Two files change:

1. millicast/broadcast/publishing-parameters.md — new enableUTCInsertion row in the parameters table (alphabetical, after audioOnly). Covers: what it does, H.264-only + RTMP/SRT scope (not WebRTC ingest passthrough, not H.265), the onFi/AMF preservation + mixed-clock caveat, seiKeyFrameOnly interaction (passthrough limited to keyframes; transcoded layers always per-frame), and configuration surfaces/precedence (URL param > publishing-token setting > account-level default). Links to the frame-metadata page for the consumer/verification path.

2. millicast/playback/frame-metadata.md — new "Server-Inserted UTC Timecode" section under Timecode Metadata. Explains that the SEI reuses the same UUID as onFi (9a21f3be-…) so players parse it identically (no player-side change), and documents behavior across the three processing modes:

Processing mode	Default (seiKeyFrameOnly=false)	seiKeyFrameOnly=true
Passthrough layer	Every frame	Keyframes only
Transcoded layer	Every frame	Every frame (setting does not apply)

Also covers transcode-with-a-passthrough-layer (mix of the two), the per-frame fresh timestamp value, and the onFi/AMF non-overwrite guarantee.

The parameters-table column padding was re-flowed by prettier (repo version) because the new row is the widest cell — hence whitespace-only churn on surrounding rows. prettier --check passes.

Notes for reviewers

• Precedence, UUID reuse, and per-mode SEI behavior were verified against the merged media-server implementation (RtmpValidator.js, H264Packetizer.cpp, rtmppacketizer.cpp, h264encoder.cpp). The admin feature flag (highest priority in the media server) is internal-only and intentionally omitted from customer docs.
• WebRTC/WHIP ingest passthrough is intentionally called out as unsupported; H.265 is unaffected.

Link to Devin session: https://dolby.devinenterprise.com/sessions/b635c9bf3add4fd393c2280136e1c01f
Requested by: @bcostdolby

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[devin-ai-integration]

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[dcoffey3296]

@bcostdolby can we also add a detail on how this is applied at the publishing token?

[devin-ai-integration]

Happy to add this. The row currently notes only that a token-level setting takes precedence over the URL param. Before documenting how it's applied at the token, we should confirm the customer-facing mechanism, since the utcInsertion feature flag is set on the token via internal admin tooling today — I want to avoid documenting a self-serve path that doesn't exist publicly.

@bcostdolby — is enabling utcInsertion on a publishing token something customers do themselves (dashboard / Customer API when creating a token), or is it applied by Dolby/support on request? Once you confirm, I'll add a short sentence (or a "Publishing token" subsection) describing the exact steps.

[devin-ai-integration]

Devin Review found 1 new potential issue.