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.

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