How to enable exclusive mode on Mac use SFBAudioEngine

[gaoyingqi]

How to enable exclusive mode on Mac use SFBAudioEngine

[sbooth]

Enabling hog mode on the device is a multi-step process:

1. Get the audio device ID from the player using outputDeviceID
2. Set the property kAudioDevicePropertyHogMode on the device using AudioObjectSetPropertyData to the appropriate process ID, usually the result of getpid()

See startHogging() in CAAudioHardware for an example.

[gaoyingqi]

Thank you so much for your helpful answer.​ I will look into it carefully.​

[gaoyingqi]

I hope that the SFBAudioEngine player can dynamically adjust its settings based on the sample rate and bitstream of each audio file it plays, while also enabling exclusive mode. Currently, I am attempting to change the sample rate via the device's setNominalSampleRatemethod within the player's decodingCompletecallback. However, an exception occurs when reconnecting the output using engine.connect(engine.mainMixerNode, to: engine.outputNode, format: format).

[gaoyingqi]

What should I do

[sbooth]

Exclusive mode and automatic sample rate switching are somewhat separate from an SFBAudioEngine standpoint.

Exclusive Access

For exclusive device access I recommend taking hog mode before calling play on the player and releasing it when the playback state changes to .stopped in the delegate notification.

Sample Rate Switching

To automatically switch the device sample rate, before playing or enqueuing a decoder you could do something like:

1. Get the sample rate of the audio to be played
2. If it doesn't match the device sample rate, determine what sample rate you'd like to use
3. Set the device's nominal sample rate to the one you've selected
4. Wait for the device's sample rate to update
5. SFBAudioEngine will generally handle the reconfiguration of the audio processing graph after the change and will call audioPlayerAVAudioEngineConfigurationChange
6. Once the desired sample rate change effect play the desired decoder

[gaoyingqi]

hi
When selecting an audio device in SimplePlayer, I invoke try? device.startHogging().After doing so, player.setOutputDeviceID() allows playback to run in exclusive mode as expected.Nevertheless, switching the audio output on macOS will trigger AVAudioEngineConfigurationChangeNotification,which results in the automatic change of the output device.

[gaoyingqi]

Can we make the player fix the output device by using setOutputDeviceID?

[gaoyingqi]

The Sample Rate Switching function works properly, but the hog mode has quite a few issues.
Whether we enable hog mode first and then call setOutputDeviceID, or call setOutputDeviceID first and then enable hog mode, the playback will switch to another audio device automatically.

[sbooth]

It's possible that exclusive access and AVAudioEngine don't play well together. There are many pieces of functionality from AUGraph that don't work with AVAudioEngine and this could be one.