[Enhancement]Stereo playout

[ipavlidakis]

Summary

This revision adds support on ADM for stereo playout control. The changes were made in the audio_engin_device and specifically target the AVAudioEngine deviceModule.

Usage

The ADM now provides API that can be observed around StereoPlayout availability and status. In order to toggle Stereo Playout based on the current route or user input you can do the following

let prefersStereoPlayback = true/false // User option
let currentRouteSupportsStereoOutput = true/false // Driven by AVAudioSession route change notifications

let enableStereoPlayout = prefersStereoPlayback && currentRouteSupportsStereoOutput
adm.isVoiceProcessingBypassed = enableStereoPlayout // if stereo is enabled we bypass VP
adm.setVoiceProcessingEnabled(!enableStereoPlayout) // if stereo is enabled then VP should be disabled
adm.isStereoPlayoutEnabled = enableStereoPlayout // activate stereoPlayout

[Copilot]

Pull Request Overview

Adds stereo playout support to the audio engine and exposes availability/enabled properties in the Objective-C API.

• Introduces API properties to query and toggle stereo playout.
• Implements engine-side stereo channel negotiation, route capability checks, and voice processing overrides.
• Extends engine state management and render paths to handle variable (mono/stereo) output channels.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
sdk/objc/api/peerconnection/RTCAudioDeviceModule.h	Adds stereo playout availability and enablement properties to public API.
sdk/objc/api/peerconnection/RTCAudioDeviceModule.mm	Implements property accessors and setter invoking native stereo playout logic.
modules/audio_device/audio_engine_device.h	Extends EngineState, state update logic, and public/internal methods for stereo handling.
modules/audio_device/audio_engine_device.mm	Adds stereo capability checks, playout channel negotiation, voice processing override/fallback, and channel-aware render paths.

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[Copilot]

[nitpick] The voice processing restore logic is duplicated in two branches (requested_channels fallback and mono route case). Extract this into a helper (e.g. RestoreVoiceProcessingIfNeeded(state, restore_voice_processing)) to reduce duplication and future maintenance risk.

[Copilot]

[nitpick] Using __bridge_transfer when removing the existing observer releases the retained object during removeObserver, which is unconventional; removeObserver does not assume ownership. Prefer (__bridge id) for removal followed by CFRelease/ARC release to avoid unintended lifetime side effects, or wrap observer management in a RAII/objc helper.

Suggested change

	[center removeObserver:(__bridge_transfer id)configuration_observer_
	name:AVAudioEngineConfigurationChangeNotification
	object:nil];
	[center removeObserver:(__bridge id)configuration_observer_
	name:AVAudioEngineConfigurationChangeNotification
	object:nil];
	CFRelease(configuration_observer_);