User reports capture-side audio (mic -> remote) is clean but
local playback (remote -> speaker via VPIO render callback) is
'broken and poor' at +65. The pipeline appears correct on paper:
fill_buffer -> downmix (L+R)*0.5 -> gain -> clamp -> i16 -> VPIO.
No errors logged. To stop guessing, add structured logging
inside the render callback so the next test cycle yields data
about what's actually flowing through.
Diagnostic emitted every 100th callback (~2 s at iOS's typical
20-50 Hz callback rate):
ios VPIO render callback diagnostic sample
cb=<counter>
num_frames=<N> VPIO buffer size in mono samples.
Expected ~960 (20ms) or ~1104 (23ms).
Outliers point at format mismatch.
peak_stereo_f32=<f32> Peak |sample| of AudioHandler's
output BEFORE gain + downmix.
0.0 = handler is producing silence
(jitter underrun, no audio).
~1.0 = full-scale content reaching
the callback as expected.
peak_out_i16=<i16> Peak |sample| of the downmixed mono
i16 we write to VPIO. Zero with
non-zero peak_stereo = downmix bug.
Near 32767 = clipping pressure.
gain=<f32> Current master output gain.
What we'll be able to diagnose from a 5-second talker session:
* peak_stereo_f32 = 0 throughout
-> AudioHandler isn't producing samples. Inbound forwarder
may not be feeding it, or jitter buffer is stuck in
buffering_samples state. NOT a render-callback bug.
* peak_stereo_f32 oscillating, peak_out_i16 = 0
-> Downmix or i16 cast is broken. Math bug in the loop.
* num_frames wildly different from ~960-1104
-> StreamFormat got rejected and VPIO is delivering a
different rate. Format-pinning fight with the session.
* peak_stereo_f32 normal AND peak_out_i16 normal AND user
still says 'broken'
-> The signal reaches the device cleanly but iOS's VPIO
output processing (AEC residual subtraction, AGC
compression, NS gate) is mangling it after our callback
returns. That's a VPIO-config problem, not a render-
callback problem; fix is to disable specific VPIO
voice-processing properties on the unit before
initialize().
Pure diagnostic commit. No behavioural change beyond a
warn-rate-limited info log line every ~2 seconds. Cost in the
audio thread is one branch + counter increment + (every 100th)
a tracing macro invocation.
Build counter 65 -> 66.
EdisonJwa
63cbab901e