# Audio Unit AEC Test

## Modify WebRTC source code
1. Hack `voice_processing_audio_unit.mm`

2. Add `kAUVoiceIOProperty_BypassVoiceProcessing`
- `enable_aec`: 0 is enable, 1 is disable

  // QNAP(Chungyi): Force enable built-in AEC - 2020/06/09
  UInt32 enable_aec = 0;
  result =
      AudioUnitSetProperty(vpio_unit_,
                           kAUVoiceIOProperty_BypassVoiceProcessing,
                           kAudioUnitScope_Global, kOutputBus, &enable_aec,
                           sizeof(enable_aec));
    if (result != noErr) {
      RTCLogError(@"Failed to set built-in AEC."
                   "Error=%ld.",
                  (long)result);
    }

- Definision in headers:

- Reference: [Official Doc](https://developer.apple.com/documentation/audiotoolbox/kauvoiceioproperty_bypassvoiceprocessing)

> Note:
> https://developer.apple.com/documentation/avfoundation/audio_track_engineering/using_voice_processing
按照這個官方的sample code: AudioEngine也有bypassing的參數，我剛剛run起來測試：
當一邊播聲音依邊路自己的聲音時，bypass有開的話：錄到的音黨會伴隨稍早自己播放的音樂
bypass關閉的話則只會有自己的聲音。
所以研判這個參數:
bypass on (1): mic會錄到自己喇叭播放的聲音
bypass off (0): 背景音會被過濾掉
所以我想我們在audio unit層把 kAUVoiceIOProperty_BypassVoiceProcessing設定成0應該就是不要錄到自己喇叭播放的聲音，讓人聲比較清楚一點這樣

- - -

## Test

- Two Devices:
- Device A
- Two KoiTalk app
- non_aec
- aec
- Device B
- KoiTalk app without aec

- Methods:
- Device B:
- Mic off
- video off
- host network
- volume to speaker

- Device A:
- Mic on
- Video off
- host network
- Disable remote audio volume

- Result: