Two audio fixes on the V3 planner and transcode pipeline:
- Copied DTS in an HLS route drags Media3's audio clock (device stall
corrections, ~0.3x pacing, frozen position reports). DTS/TrueHD/PCM
are not HLS-native codecs regardless of the client's progressive
decode claims, so HLS remux routes now convert them to AAC. Validated
on the Shield: the copy-remux fallback went from ~0.3x pacing to
exactly real time.
- Transcodes no longer hard-downmix to stereo: multichannel sources
keep 5.1 through the AAC re-encode (384k, -ac 6), plumbed through
TranscodeOpts, the planner result, and the transcode-node protocol
(new optional target_audio_channels field, ignored by older nodes).
Also logs one "playback plan decided" line per V3 start (decision
reason, delivery, play method, DV profile, quality inputs) so route
selection is reconstructible from server logs alone.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
