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wt-publish: force explicit AAC-LC stereo mapping

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every.channel 2026-02-24 23:06:30 -08:00
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# ECP-0077: Explicit AAC-LC Live Audio Profile In `wt-publish`
## Context
Live OTA inputs expose multiple AC-3 audio tracks (5.1 + stereo language variants). Browser watcher behavior is more stable when the published relay stream has a single explicit AAC-LC stereo track shape.
## Decision
In `ec-node wt-publish` transcode mode, force explicit stream mapping and AAC profile:
- `-map 0:v:0`
- `-map 0:a:0?`
- `-c:a aac`
- `-profile:a aac_low`
- `-b:a 160k`
- `-ac 2`
- `-ar 48000`
## Rationale
- Removes ambiguity from ffmpeg auto stream selection when multiple audio tracks exist.
- Keeps audio encoding browser-friendly and deterministic.
- Preserves optional audio behavior (`0:a:0?`) for edge cases where input temporarily lacks audio.
## Reversibility
- Revert to ffmpeg auto mapping/profile by removing explicit `-map` and `-profile:a` flags.