I am developing an application which does custom audio processing and sends the processed audio to the USB headset. My requirement is that the USB headset should not be visible to the user in the list of Audio output devices in System Preferences. Using "SampleUSBAudioOverrideDriver" code-less kext sample code from Apple, I'm able to change the interface name but I really need to hide it.
Is subclassing AppleUSBAudioDevice an option?
The recommended way to do pre-processing of a USB audio device's input and output streams in kernel space is to use the AppleUSBAudioPlugin API. This kext does not appear in the list of devices because it isn't an instance of IOAudioEngine, so there is no "hiding" involved.
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I'm developing driver for USB video capture device. First of all, I've started with CoreMediaIO sample:
https://developer.apple.com/library/content/samplecode/CoreMediaIO/Introduction/Intro.html
The kernel extension is based on IOVideoSample. It gets data from the USB device and sends to the assistant. Kext has IOKitPersonalities based on the USB device. So the device is real and should support HotPlug. Kext main class loads when the device is plugged in and unloads when the device is plugged out.
SampleAssistant was changed only to detect my kext class. PlugIn has NoCMIOHardwarePluginLazyLoadingInfo property.
When all video capture apps are closed - hotplug works well. Terminate function is being called from kext and kext object is being unloaded without any problem.
Even if you start video capture app with the stream from the device, then close it and plug out device - hotplug also works.
It works well with QuickTime player. It can find a stream and show an image, but there is one problem.
When QuickTime (or any other video capture app) works and show stream from the device - hotplug doesn't work. If you try to plug out the device it will remain in the system and USB port won't work until you reboot Mac. According to logs - terminate function wasn't called at all. Seems that something retains a link to the device.
I've started digging into the problem.
First of all, I figured out that SampleAssistant doesn't support hotplug by default. It has notification only for device arriving (DeviceArrived). I've added "interest" notification and handle only "kIOMessageSeviceIsTerminated" message - executing DeviceRemoved function and force deleting device object, but it didn't help.
There is also a file CMIO_DPA_Sample_Server_Stream.cpp. If you go to Stream::Start function and delete "mIOSAStream.Open;" and "mIOSAStream.Start();" lines - hotplug works.
Can you please advise what can be done to solve this problem?
I am developing a audio driver to do some custom audio processing using audio reflector driver sample code from Apple. Output from audio reflector driver is passed to real USB audio hardware device using core audio application. Now I want to hide USB audio hardware device from the system preferences so that user is not able to select the USB audio hardware output device as the default output device. Using the "SampleUSBAudioOverrideDriver" codeless kext I am able to change the name of output interface but not hide it. Any idea on how I will be able to hide USB audio hardware output device.
Thanks in advance.
Vin Pai
After a lof of R&D on this topic, I found that codeless kext provided in the sample code, SampleUSBAudioOverrideDriver doesn't use the property set to hide the device interface.
I'm working on an application that plays audio on OsX. I'm able to list the available output devices with CodeAudio, but I have issues with a bluetooth headset; Even though the device is powered off and not connected, it's still listed in the OsX sound pref pane, and therefore picked up by CoreAudio as a valid output.
I'd like not to display bluetooth outputs if the corresponding device isn't connected already.
I've tried to check CoreAudio properties like those:
kAudioDevicePropertyDeviceIsAlive
kAudioDevicePropertyDeviceIsRunning
kAudioDevicePropertyDeviceIsRunningSomewhere
but there's no difference between the default output and the bluetooth output.
Is this kind of detection something doable with Coreaudio?
For the benefit of future searchers the way I've done it in the past is to:
Enumerate the detected devices
Query the kAudioDevicePropertyTransportType property for each AudioDeviceID
which will return a transport type ID constant.
Match for the
kAudioDeviceTransportTypeBluetooth or
kAudioDeviceTransportTypeBluetoothLE type
That way you can determine the type of connection the device is using (USB, Firewire etc). You can find the full list of transport types in AudioHardwareBase.h
There are two apps for OS X that allow you to pre-amplify audio before it gets played by the hardware: Audio Hijack (pre-amplifies output from particular applications) and Boom (pre-amplifies all system audio). These apps work by applying equalization to pre-existing audio streams - with a high pre-amp setting - before they are sent to the sound card.
My question is: how to hijack the system audio stream and then send it along to the sound card. Is this somewhere in an API, or would it require altering a system library ?
1) Create a standard sound device that shows up in audio system preferences. This has to be in the form of a kernel extension (kext). Difficult to create by just reading apple docs - try looking at an app called Soundflower.
2) Once you've loaded the kext and have the new audio device available, select it in preferences as the default output device for system audio.
3) Now you need to alter the audio and pipe it to the real system output. This can be done in an accompanying application that adds callback "IOProc" functions to a) the new device and b) your computer's built-in output device. You can then copy audio buffers from one device to the other, to pipe the audio to your speakers. To increase the volume, multiply all the bytes in the buffer by some factor. See Soundflower's accompanying app.
I am currently using the Mac OS X Audio Queue Services API for audio recording and sound analysis. Works fine using the default mic input.
If there is more than one microphone plugged into the Mac (USB, headset jack, etc.), is there a way to programmatically enumerate and select which mic is to be used for audio input within an application? (e.g. not have to send the user to the system preferences panel, which may affect a users other audio applications.) If so, which APIs should be used to select the mic input.
To enumerate available input devices please see my answer to AudioObjectGetPropertyData to get a list of input devices.
Once you've determined the input device you'd like to use, you can set the kAudioQueueProperty_CurrentDevice property to the device's UID.
I fear, no, because AQ is hard-coded to use default input (to my best knowledge). AQ is fairly limited and only iOS gives more control via AutoSessions. However, you can use AUHAL to record from an arbitrary device:
http://developer.apple.com/library/mac/#technotes/tn2091/_index.html
You won't need listing 4 from above because you'll use the AudioDeviceID for the device you have chosen (presumably by getting the list of devices using AudioObjectGetPropertyDataSize and picking the one you want).
FWIW: if you decide that's too much, you can presumably still use AudioHardwareSetProperty to set kAudioHardwarePropertyDefaultInputDevice from your code - not what you wanted but certainly less work...
If you set up the Audio Queue to read from the default input device, then it will read from the mic that is selected as default in the System Preferences->Soubd->Input tab.