User report after the 8x boost commit (e85a6d3): playback STILL
broken, but now the diagnostic clearly shows the actual problem.
Render-callback peak_out_i16 SATURATES at 32767 on speech peaks
(cb=600, 1100, 1200, 2400) because the 8x boost amplifies an
already-loud signal into hard clipping. Quiet content reaches
audible level but loud peaks are catastrophically distorted.
The 8x boost was treating the wrong cause.
Real root cause (researched online after user prompted: 'this is
iOS a popular platform, there must be solutions'): iOS has TWO
independent audio channels:
In-call channel (.voiceChat / .videoChat modes)
* Routes through the phone-call audio path.
* Aggressively ducks non-voice content to the earpiece.
* Volume controlled by a separate in-call hardware
register, not the side buttons when not actively on a
phone call.
Media channel (.default mode)
* Routes through the standard media playback path.
* No automatic ducking.
* Volume controlled by the side volume buttons normally.
With AVAudioSession mode .voiceChat, iOS sends our output
through the in-call channel which plays at 'earpiece-level'
loudness on the speaker too. Signal is technically present but
buried under the speaker's noise floor. With mode .default +
.defaultToSpeaker option, output routes via media channel and
plays at normal loudness.
Both Twilio (video-quickstart-ios) and Daily.co (patched WebRTC
module) document the same workaround and use VPIO for AEC while
keeping the session mode at .default for loud playback:
github.com/twilio/video-quickstart-ios/issues/522
stackoverflow.com/questions/79834998 (Daily.co)
The user also noticed 'tx/rx almost no changes even receiving
packages' \u2014 likely a misinterpretation of the frames counter
not advancing as fast as expected during quiet voice; AudioHandler
returns silence when its jitter buffer is in buffering_samples
state which doesn't fire 'decode failed' but also doesn't
increment frames_received. The real issue is still the playback
ducking; the counter behaviour is a downstream symptom.
Changes:
1. AppDelegate.swift: AVAudioSession mode .voiceChat -> .default
with options [.defaultToSpeaker, .allowBluetoothHFP,
.allowBluetoothA2DP]. VPIO continues to do its job (AEC, NS,
AGC on the mic side); only the playback routing changes.
The earlier 'speaker selector silent under .default' bug
does NOT apply because we no longer use cpal RemoteIO \u2014
VPIO honours overrideOutputAudioPort under any mode.
2. ios_voice_unit.rs: revert the 8x output boost from e85a6d3.
With media-channel routing, signal levels are correct and
no software amplification is needed. Render callback restored
to plain (l+r)*0.5*gain downmix.
3. ios_voice_unit.rs: revert the BypassVoiceProcessing toggle
from c16318c. The VPIO chain stays enabled so we keep
capture-side AEC/AGC/NS for free \u2014 the playback breakage
it was trying to fix was the wrong layer all along.
4. ios_voice_unit.rs: drop the diagnostic render-callback log
line. Production-clean code; can be re-enabled by reverting
the diff in the closure if future debugging needs it.
Build counter 69 -> 70.
EdisonJwa
6e0bf21295