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# Overview This CL chain exposes new API from ObjC WebRTC SDK to inject custom means to play and record audio. The goal of CLs is achieved by having additional implementation of `webrtc::AudioDeviceModule` called `ObjCAudioDeviceModule`. The feature of `ObjCAudioDeviceModule` is that it does not directly use any of OS-provided audio APIs like AudioUnit, AVAudioEngine, AudioQueue, AVCaptureSession etc. Instead it delegates communication with specific system audio API to user-injectable audio device instance which implements `RTCAudioDevice` protocol. `RTCAudioDevice` is new API added to ObC WebRTC SDK in the CL chain. # AudioDeviceBuffer `ObjCAudioDeviceModule` does conform to heavy `AudioDeviceModule` interface providing stubs for unrelated methods. It also implements common low-level management of audio device buffer, which glues audio PCM flow to/from WebRTC. `ObjCAudioDeviceModule` owns single `webrtc::AudioDeviceBuffer` which with the help of two `FineAudioBuffer` (one for recording and one for playout) is exchanged audio PCMs with user-provided `RTCAudioDevice` instance. `webrtc::AudioDeviceBuffer` is configured to work with specific audio: it has to know sample rate and channels count of audio being played and recorded. These formats could be different between playout and recording. `ObjCAudioDeviceModule` stores current audio parameters applied to `webrtc::AudioDeviceBuffer` as fields of type `webrtc::AudioParameters`. `RTCAudioDevice` has it's own variable audio parameters like sample rate, channels count and IO buffer duration. The audio parameters of `RTCAudioDevice` must be kept in sync with audio parameters applied to `webrtc::AudioDeviceBuffer`, otherwise audio playout and recording will be corrupted: audio is sent only partially over the wire and/or audio is played with artifacts. `ObjCAudioDeviceModule` reads current `RTCAudioDevice` audio parameters when playout or recording is initialized. Whenever `RTCAudioDevice` audio parameters parameters are changed, there must be a notification to `ObjCAudioDeviceModule` to allow it to reconfigure it's `webrtc::AudioDeviceBuffer`. The notification is performed via `RTCAudioDeviceDelegate` object, which is provided by `ObjCAudioDeviceModule` during initialization of `RTCAudioDevice`. # Threading `ObjCAudioDeviceModule` is stick to same thread between initialization and termination. The only exception is two IO functions invoked by SDK user code presumably from real-time audio IO thread. Implementation of `RTCAudioDevice` may rely on the fact that all the methods of `RTCAudioDevice` are called on the same thread between initialization and termination. `ObjCAudioDeviceModule` is also expect that the implementation of `RTCAudioDevice` will call methods related to notification of audio parameters changes and audio interruption are invoked on `ObjCAudioDeviceModule` thread. To facilitate this requirement `RTCAudioDeviceDelegate` provides two functions to execute sync and async block on `ObjCAudioDeviceModule` thread. Async block could be useful when handling audio session notifications to dispatch whole block re-configuring audio objects used by `RTCAudioDevice` implementation. Sync block could be used to make sure changes to audio parameters of ADB owned by `ObjCAudioDeviceModule` are notified, before interrupted playout/recording restarted. Bug: webrtc:14193 Change-Id: I5587ec6bbee3cf02bad70dd59b822feb0ada7f86 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/269006 Reviewed-by: Henrik Andreasson <henrika@google.com> Commit-Queue: Yury Yarashevich <yura.yaroshevich@gmail.com> Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org> Reviewed-by: Henrik Andreassson <henrika@webrtc.org> Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org> Cr-Commit-Position: refs/heads/main@{#37928}
WebRTC Obj-C SDK
This directory contains the Obj-C SDK for WebRTC. This includes wrappers for the C++ PeerConnection API and some platform specific components for iOS and macOS.
Organization
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api/
Wrappers around classes and functions in the C++ API for creating and configuring peer connections, etc.
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base/
This directory contains some base protocols and classes that are used by both the platform specific components and the SDK wrappers.
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components/
These are the platform specific components. Contains components for handling audio, capturing and rendering video, encoding and decoding using the platform's hardware codec implementation and for representing video frames in the platform's native format.
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helpers/
These files are not WebRTC specific, but are general helper classes and utilities for the Cocoa platforms.
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native/
APIs for wrapping the platform specific components and using them with the C++ API.
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unittests/
This directory contains the tests.