How to play audio via a USB sound card using libao?

Question

I get the following from aplay -l, lsusb.

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pi@raspberrypi:~ $ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Device [USB PnP Sound Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Device_1 [USB PnP Sound Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
pi@raspberrypi:~ $ lsusb
Bus 001 Device 005: ID 046d:c31c Logitech, Inc. Keyboard K120 for Business
Bus 001 Device 008: ID 0d8c:013c C-Media Electronics, Inc. CM108 Audio Controller
Bus 001 Device 007: ID 0d8c:013c C-Media Electronics, Inc. CM108 Audio Controller
Bus 001 Device 006: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 001 Device 004: ID 1bcf:0005 Sunplus Innovation Technology Inc. 
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

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I want to play my MP3 via CM108 Audio Controllers with libao. I tried these:

ao_initialize();
ao_option aoption;
ao_option *poption;
poption = &aoption;
poption->key = (char*)"dev";
poption->value = (char*)"hw:0";
dev = ao_open_live(driver, &format, poption); 
    while (mpg123_read(mh, buffer, buffer_size, &done) == MPG123_OK)
        ao_play(dev, (char *)buffer, done);

So sound is played via the Pi successfully. I understand that hw:0 is a sound card of the Pi. What should I use instead of hw:0 if I want to play via the first or second CM108 Audio Controller? I already tried hw:1 and hw:2 and it does not work.

Answer 1

Use the full Alsa designation from output of aplay -l, so in your case the first sound card is hw:0,0, the first usb card is hw:1,0 and the second usb card is hw:2,0.

If you install mpg123 and your sound file is called test.mp3 then use following:

mpg123 -o alsa -d hw:1,0 test.mp3

Note that -o alsa will attempt to play the file via alsa, omitting this uses system default (alsa or pulse) whatever is installed. So

mpg 123 -d hw:2,0 test.mp3

will also work on the second usb card using the default sound server (alsa or pulse) on your system.