External code review pushed back on the 'iPhone speaker hardware
distortion' hypothesis and pointed out we need more than just
peak measurements. The reviewer's checklist:
* peak_i16
* rms_i16
* num_clipped_samples (abs >= 32767)
* zero_fill_count / underrun_count
* callback_frame_count variability
* decoded_packet_duration_ms
* input_was_zero
* actual ASBD / actual sample rate
The format diagnostics at +71 already showed iOS honoured
48 kHz Int16 mono on both buses and that .default mode +
.defaultToSpeaker routed to the speaker correctly with
outputVolume=0.45. So format + route are confirmed correct.
The remaining mystery is WHY 'loud but distorted' \u2014 we need
sample-level metrics to isolate where in the pipeline the
breakage occurs.
This commit instruments the VPIO render callback with:
* num_frames + frames_changes : detects iOS re-negotiating
buffer size between callbacks
(which would imply jitter the
fixed scratch_stereo Vec can't
absorb cleanly).
* peak_stereo + rms_stereo : characterises AudioHandler's
output BEFORE our downmix.
Distinguishes 'real audio
arriving' from 'silence'.
* peak_out_i16 + clip_count : measures what we hand VPIO.
clip_count > 0 means we're
clipping at our boundary even
with gain=1.0 \u2014 indicates
upstream is over-driven.
* input_was_zero : explicit silence/no-talker
indicator separate from peak=0
which could mean tiny content
rounded to 0.
Reviewer's preferred diagnostic path is to dump PCM to file
and play with ffplay externally; that's iOS-impractical
without a shared filesystem path the user can extract via
Files.app. Instead we sample the same metrics in-callback at
~2 Hz which gives us the same information at run time.
Pure diagnostic. No behavioural change. Counters live in the
FnMut closure so the audio thread cost is one branch +
counter increment per callback, plus a one-pass RMS sum +
peak scan every 100 callbacks.
Build counter 71 -> 72.
Reviewer also recommended a headphone test in parallel \u2014
that will be done by the user (out-of-band) at the next
test cycle to determine whether the symptom changes when
audio leaves the speaker path.
EdisonJwa
53e09ea091