[alsa-devel] Attempting to understand odd snd-usb-audio code and behavior

[Keith A. Milner]

On Wednesday 23 Aug 2017 14:52:43 Clemens Ladisch wrote:
> Keith A. Milner wrote:
> >>> kernel: [ 1987.452947] usb 1-1: Unable to change format on ep #8e:
> >>> already in use> 
> > So the error messages are due to a userspace app trying to open playback
> > and capture at the same time?
> 
> For this device, playback requires a running capture stream to determine
> the rate of packets.  This error happens when the application tries to
> open the capture stream after the playback stream.  (If the format does
> not actually need to change, the error message is misleading.)
> 
> Your actual problem is that the device does not send any capture packets.

Thank you for the clarification. Hopefully I will find some time to explore 
this further.

Cheers,

Keith