树莓派Airplay将有线音箱变成WiFi音箱

docker run -d --restart unless-stopped --net host --device /dev/snd \
    mikebrady/shairport-sync -a DenSystem -- -d hw:0 -c PCM

root@rpi0:~# grep output_device ./shairport-sync/audio_alsa.c -C 2
    // this is very crude -- if the device is a hardware device, then it's assumed the delay is
    // precise
    const char *output_device_name = snd_pcm_name(alsa_handle);
    int is_a_real_hardware_device = 0;
    if (output_device_name != NULL)
      is_a_real_hardware_device = (strstr(output_device_name, "hw:") == output_device_name);

    // The criteria as to whether precision delay is available
--
        warn("The output device \"%s\" is busy and can't be used by Shairport Sync at present.",
             alsa_out_dev);
      debug(2, "the alsa output_device \"%s\" is busy.", alsa_out_dev);
    } else if (ret == -ENOENT) {
      die("the alsa output_device \"%s\" can not be found.", alsa_out_dev);
    } else {
      char errorstring[1024];
--

    /* Get the Output Device Name. */
    if (config_lookup_string(config.cfg, "alsa.output_device", &str)) {
      alsa_out_dev = (char *)str;
    }

root@rpi0:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Headphones [bcm2835 Headphones], device 0: bcm2835 Headphones [bcm2835 Headphones]
  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 1: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

iw dev wlan0 set power_save off

mkdir -p /home/shairport-sync/.config/pulse
chown -R shairport-sync:shairport-sync /home/shairport-sync/

output_device = "hw:3";
mixer_control_name = "Speaker";