Hello. I sent this message previously before I solidified my membership to the list and it seems my message never posted. Here it is again. My apologies if did go through and I missed it.

I am new to audio development in Linux. I have worked with user space development with respect to UVC code and I have worked with specifying an XU in UVC. I wrote a user space driver/application to talk to a device supporting the UVC XU in Linux. I am trying to specify an extension to the UAC specification and then write a user space driver/application to use the extension when a device that supports it is available in Linux. Pretty much the same situation as I have already done with UVC XU. Windows and Mac code will follow, but right now I am only concerned with Linux.

Can anyone assist me with the best path forward for writing user space code to use the XU I am going to define? Meaning generically speaking how to use UAC XU controls in ALSA. I was looking for code samples that use the audio.h header file interface, but after a day and a half I am coming to conclusion that only kernel space uses audio.h and that I will need to go through ALSA to accomplish my task. Again, this will be user space code I want distribute easily, with minimal dependencies. Our code will be apache licensed afterwards if possible, just like our UVC code was. So any work I do should be freely available to the community afterwards. **EDIT FROM PREVIOUS MESSAGE** After more searching, it appears that any XU controls would be processed through usbmixer.c, but I don't see how to use the code in usbmixer from user space. And so far I can't tell what source usbmixer resides in. I downloaded the alsa-lib source in Fedora, but I don't see that file. Is this a Linux kernel file? So far I am having lots of trouble finding anything useful regarding audio XUs in Linux. My apologies if this should be simple. Thank you in advance for any assistance.

Best Regards,

Brent