39 lines
1.3 KiB
Markdown
39 lines
1.3 KiB
Markdown
# ECP-0077: Explicit AAC-LC Live Audio Profile In `wt-publish`
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Status: Implemented
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## Context
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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.
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## Decision
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In `ec-node wt-publish` transcode mode, force explicit stream mapping and AAC profile:
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- `-map 0:v:0`
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- `-map 0:a:0?`
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- `-c:a aac`
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- `-profile:a aac_low`
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- `-b:a 160k`
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- `-ac 2`
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- `-ar 48000`
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## Rationale
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- Removes ambiguity from ffmpeg auto stream selection when multiple audio tracks exist.
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- Keeps audio encoding browser-friendly and deterministic.
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- Preserves optional audio behavior (`0:a:0?`) for edge cases where input temporarily lacks audio.
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## Alternatives considered
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- Keep ffmpeg auto stream selection/profile defaults. Rejected because multi-track OTA inputs produced unstable browser outcomes.
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- Preserve AC-3 passthrough for all sources. Rejected because browser compatibility is weaker than explicit AAC-LC stereo.
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## Rollout / teardown
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- Enable explicit audio mapping/profile in `wt-publish` transcode mode and verify browser playback across OTA sources.
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- Teardown by removing explicit `-map` and AAC profile options.
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## Reversibility
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- Revert to ffmpeg auto mapping/profile by removing explicit `-map` and `-profile:a` flags.
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