With Audio Passthrough on, every (E-)AC-3 track on Apple TV dropped
100-220ms of audio every 1.79s. The system pipeline behind the
compressed AVPlayer path reads unboundedly far ahead of the playhead
and consumes its buffer in fixed ~1.8s quanta; the AO's 2s feed lead
meant each refill overran the write head and the renderer skipped the
missing audio to stay on clock. Bitrate- and route-independent, and
invisible to the AO: item status, time control, and the feed margin
all stayed clean while the sink output gapped (#1300, #1776).
MPVKit 1.0.25 feeds the elementary stream 8s ahead of the observed
playhead -- 4x the pipeline's refill quantum -- sizes the ES window
from the configured lead, exposes it as
--ao-avfoundation-compressed-lead, and keeps waiting during preroll
while a slow source (a realtime-pinned server transcode) is still
making priming progress instead of abandoning Atmos for PCM.
Verified on an Apple TV 4K gen 3 with an HDMI audio capture rig
against EAC3 768k and 640k streams: 21 dropouts/min on 2.15.0, zero
across 10.7 minutes with the new lead; a 997Hz sine encoded as EAC3
through the full passthrough path is statistically identical to
first-party AVKit playback of the same tone; a rate-limited server at
0.95x realtime now prerolls late on the compressed path instead of
downgrading, and once the lead is filled mpv's cache pauses absorb
the deficit with the margin intact.
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