how to channel mask for alsasrc under gst-launch?

[Charlie Laub]

I'm using a USB audio interface under Ubuntu/ALSA. It has 6 input channels
and 10 output channels. I am having problems getting input working correctly
with this device with gstreamer. I believe that this has to do with the
bitmask that gstreamer assumes for the input. 

 

When I look at debug output I see that it is using
channel-mask=(bitmask)0x3f. This is certainly correct for, e.g. 7.1 audio,
however, I think this is incorrect for my audio interface. I know that the
output channel bitmask for this device is 0x000, and I need to set all
output channels to channel-mask=-3 when I sink my pipeline to this device. I
assume that the input (alsasrc) bitmask also needs to be set to 0x000,
however, I have not been able to find a way to do this. I am using Gstreamer
version 1.8.3

 

When I tell gstreamer to use the audio interface as the source for the
pipeline all I get it a kind of "ground loop hum" type of noise. If I use a
separate program to get data from the device and send it to the ALSA
loopback, and then use the loopback as gstreamer alsasrc everything works
fine.  In both cases the pipeline runs without error. The problem is
definitely within gstreamer and is very likely channel-mask related.

 

Any advice on how to solve this problem under gst-launch is appreciated.

 

Charlie Laub

 

 

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