Creating ALSA Aliases for specific devices that are then visible to userspace

[Dejan Jovasevic]

Hi there,

I was wondering if it is possible to edit /etc/asound.conf in such a way as to create alias names for specific devices, and then when a user space application enumerates audio devices have these aliases show up? My goal is to be able to create an alias for 2 hdmi playback devices (outputdev1, outputdev2 for instance), and then use this alias when searching for alsa devices in the application.
ie. outputdev1 => plughw:CARD=X,DEV=Y
outputdev2 => plughw:CARD=X,DEV=Z
I have been able to create device aliases by editing the config as follows:
pcm.outputdev1 { type plug slave { pcm "hw:1,4" } }
pcm.outputdev2 { type plug slave { pcm "hw:1,6" } }
And then using these aliases I am able to perform capture and playback using the alsa command line utilities aplay|arecord. However these aliases do not show up in my application.
Using the definition of pcm.plughw in /usr/share/alsa/alsa.conf I have been able to construct my own pcm.outputdev type. This does show up when my appliction enumerartes alsa devices, however I am unable to specify just one device, so all plughw devices show up under outputdev aswell.
DeviceName:plughw:CARD=PCH,DEV=0 DeviceName:plughw:CARD=PCH,DEV=1 DeviceName:plughw:CARD=PCH,DEV=4 DeviceName:plughw:CARD=PCH,DEV=6 DeviceName:plughw:CARD=PCH,DEV=7 DeviceName:plughw:CARD=PCH,DEV=9 DeviceName:outputdev:CARD=PCH,DEV=0 DeviceName:outputdev:CARD=PCH,DEV=1 DeviceName:outputdev:CARD=PCH,DEV=4 DeviceName:outputdev:CARD=PCH,DEV=6 DeviceName:outputdev:CARD=PCH,DEV=7 DeviceName:outputdev:CARD=PCH,DEV=9

Thank you so much in advance,

Dejan Jovasevic

[Dejan Jovasevic]

The issue was not in the way I edited the ALSA config itself, but the way user space application was getting device hints from ALSA. I was looping through sound cards and then for each card I would call

snd_device_name_hint (int card, const char *iface, void ***hints).

and get back array of hints for all devices on that card. However, when I changed the logic and instead of looping through cards I called the fucntion with -1 snd_device_name_hint(-1,....) , I got back array with hints for all cards and devices I was able to see the aliases I created.