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. If you find any problems, please report it here.

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!