Stabilize live playback audio

evolution/proposals/ECP-0114-live-playback-audio-stability.md

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+# ECP-0114: Live Playback Audio Stability
+
+Status: Draft
+
+## Problem / context
+
+Local HDHomeRun playback can sound choppy even while video continues. The current desktop bridge starts a full three-rung CMAF/HLS ladder for local watching, and each variant carries its own AAC encode. OTA MPEG-TS timestamps can also jitter enough that straight AAC transcoding preserves audible gaps or corrections.
+
+## Decision
+
+Use a playback-specific encoding profile for local watching:
+
+- local desktop playback encodes only the 720p rendition instead of the full ABR ladder;
+- all live AAC transcode paths force AAC-LC stereo and resample with timestamp compensation;
+- keep the full multi-variant ladder for publishing and sharing paths.
+
+## Consequences
+
+- Local watching spends less CPU and avoids variant-switch audio discontinuities.
+- AAC output gets a continuous 48 kHz stereo timeline even when OTA timestamps jitter.
+- Published streams remain multi-variant and manifest-compatible.
+
+## Alternatives Considered
+
+- Keep full ABR for local playback. Rejected because the local player does not need ABR to watch a LAN tuner and the separate AAC timelines make audible switching more likely.
+- Fix only the player buffer. Rejected because the source fragments should already have stable audio timestamps before they reach HLS or MSE.
+
+## Rollout / teardown
+
+Remove the playback-specific variant selection and the audio resample filter from the ffmpeg profiles.