AudioUnit is not playing back audio on tvOS

Question

I'm working on an application for tvOS platform for playing back audio using WebRTC (https://webrtc.org/). WebRTC uses AudioUnit for audio playout (https://chromium.googlesource.com/external/webrtc/+/7a82467d0db0d61f466a1da54b94f6a136726a3c/sdk/objc/native/src/audio/voice_processing_audio_unit.mm). It works perfectly on iOS, but produces errors on tvOS.

First of all I've disabled audio capturing at all. The first error happens when creating a Voice Processing IO audio unit:

// Create an audio component description to identify the Voice Processing
  // I/O audio unit.
  AudioComponentDescription vpio_unit_description;
  vpio_unit_description.componentType = kAudioUnitType_Output;
  vpio_unit_description.componentSubType = kAudioUnitSubType_VoiceProcessingIO;
  vpio_unit_description.componentManufacturer = kAudioUnitManufacturer_Apple;
  vpio_unit_description.componentFlags = 0;
  vpio_unit_description.componentFlagsMask = 0;
  // Obtain an audio unit instance given the description.
  AudioComponent found_vpio_unit_ref =
      AudioComponentFindNext(nullptr, &vpio_unit_description);
  // Create a Voice Processing IO audio unit.
  OSStatus result = noErr;
  result = AudioComponentInstanceNew(found_vpio_unit_ref, &vpio_unit_);
  if (result != noErr) {
    vpio_unit_ = nullptr;
    RTCLogError(@"AudioComponentInstanceNew failed. Error=%ld.", (long)result);
    return false;
  }

AudioComponentInstanceNew returns -3000 OSStatus (I assume it means an invalid component ID). This issue can be fixed by replacing kAudioUnitSubType_VoiceProcessingIO → kAudioUnitSubType_GenericOutput (I'm not sure this is a correct replacement, but the error is gone).

After that WebRTC is trying to enable output

// Enable output on the output scope of the output element.
  UInt32 enable_output = 1;
  result = AudioUnitSetProperty(vpio_unit_, kAudioOutputUnitProperty_EnableIO,
                                kAudioUnitScope_Output, kOutputBus,
                                &enable_output, sizeof(enable_output));
  if (result != noErr) {
    DisposeAudioUnit();
    RTCLogError(@"Failed to enable output on output scope of output element. "
                 "Error=%ld.",
                (long)result);
    return false;
  }

and this doesn't work as well: it returns -10879 OSStatus (I assume it means an invalid property). I think the problem is in providing kAudioOutputUnitProperty_EnableIO property, but have no idea why should be utilized instead.

Any ideas pr advices are very much appreciated. Thanks in advance.

AudioUnit is not playing back audio on tvOS

0 Answers