ALSA

mkchromecast can cast to google cast without the need of pulseaudio. One advantage I have seen, is that delay is maximum 4 seconds. For that, you have to use the ffmpeg or avconv backends together with the --alsa-device flag. You need to checkout the alsa branch to test this feature for the moments. This will be merged to master soon.

Example:

python mkchromecast.py --encoder-backend ffmpeg --alsa-device hw:2,1

However, some previous configuration is needed. We will try to figure out how to build the hw:X1,Y1 alsa device needed to complete a .asoundrc configuration file, and the virtual alsa device hw:X2,Y2 needed by the --alsa-device flag in mkchromecast. It seems that always Y1 has to be 0 while Y2 is 1.

How to determine hw:X1,Y1

First, check what are the cards available in your system in /proc/asound/cards. Below an example:

  % cat /proc/asound/cards                                                                                                                             
 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xc1814000 irq 57
 1 [HDMI           ]: HDA-Intel - HDA Intel HDMI
                      HDA Intel HDMI at 0xc1810000 irq 61

In the case above, the principal card is 0 [PCH]: HDA-Intel - HDA Intel PCH for which the index X1 is 0. Normally, our needed alsa sound card (hw:X1,Y1) can be built as hw:0,0. We will need it in the next step.

The ~/.asoundrc file

Second, we need to create the ~/.asoundrc shown below. Note that this file may not exist. You will need to changehw:X1,Y1 accordingly (in the case shown in this wiki is hw:0,0):

pcm.!default {
  type asym
  playback.pcm "LoopAndReal"
  #capture.pcm "looprec"
  capture.pcm "hw:X1,Y1"
}

pcm.looprec {
    type hw
    card "Loopback"
    device 1
    subdevice 0
}


pcm.LoopAndReal {
  type plug
  slave.pcm mdev
  route_policy "duplicate"
}


pcm.mdev {
  type multi
  slaves.a.pcm pcm.MixReale
  slaves.a.channels 2
  slaves.b.pcm pcm.MixLoopback
  slaves.b.channels 2
  bindings.0.slave a
  bindings.0.channel 0
  bindings.1.slave a
  bindings.1.channel 1
  bindings.2.slave b
  bindings.2.channel 0
  bindings.3.slave b
  bindings.3.channel 1
}


pcm.MixReale {
  type dmix
  ipc_key 1024
  slave {
    pcm "hw:X1,Y1"
    rate 48000
    #rate 44100
    periods 128
    period_time 0
    period_size 1024 # must be power of 2
    buffer_size 8192
  }
}

pcm.MixLoopback {
  type dmix
  ipc_key 1025
  slave {
    pcm "hw:Loopback,0,0"
    rate 48000
    #rate 44100
    periods 128
    period_time 0
    period_size 1024 # must be power of 2
    buffer_size 8192
  }
}

Test that this is working. For that, open any audio file to see if it is playing correctly.

How to determine hw:X2,Y2 and the Loopback device

We now need to load the snd-aloop module:

sudo modprobe snd-aloop

This will create a new virtual device called Loopback that we above referenced as hw:X2,Y2 and we will pass it to the --alsa-device flag of mkchromecast:

  % cat /proc/asound/cards                                                                                                                               

 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xc1814000 irq 57
 1 [HDMI           ]: HDA-Intel - HDA Intel HDMI
                      HDA Intel HDMI at 0xc1810000 irq 61
 2 [Loopback       ]: Loopback - Loopback
                      Loopback 1

As it can be seen, Loopback has an index X2 equals 2. This device is then hw:2,1. This won't survive reboot. If you want to make this permanent, add snd-aloop to /etc/modules.

Now we can execute mkchromecast passing all desired parameters:

python mkchromecast.py --encoder-backend ffmpeg --alsa-device hw:2,1 -c aac --volume

Happy Casting!