Hooking up a chromecast to a Play:1 (Play:3) without line-in

  • 1 October 2016
  • 12 replies

I got tired of waiting for Sonos to get around to release some kind of cast support (they have good reasons not to too).

Before I began this was my wish list:
  • Cast from android/iphone using chromecast,
  • it should start automatically when I cast,
  • have acceptable sound quality (I tried bluetooth with a similar setup but it sounded awful) and
  • be relatively cheap.

So, to the hardware:
  • chromecast audio (I would recommend getting a normal chromecast and extract the audio - the one I got has some limitations),
  • raspberry pi as transcoder (record output from chromecast and transform it into a mp3-stream that the sonos can handle)
  • (and a USB sound card because the raspberry has no line-in (got a behringer UCA202 which is supported)

Here is an image of the mess! :)

After installing the standard raspbian (and running the raspi-config + apt update/upgrade) I proceeded to install pulseaudio (~for capturing and monitoring), vlc (for transcoding) and sox (for sound manipulation):

** Note: I probably install way to much than is really needed... **

$ sudo apt install pulseaudio pulseaudio-module-zeroconf alsa-utils avahi-daemon vlc-nox vlc-plugin-pulse sox bc

The pulseaudio deamon should start "when needed by a client", otherwise, now is a good time to start it so do
pulseaudio --start
to start it...
Then I plugged in my USB sound capture which was connected to the chromecast (and was playing ) device it showed up directly using arecord:

$ pacmd list-sources | grep  'name:'
name: <alsa_output.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00-CODEC.analog-stereo.monitor>
name: <alsa_input.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00-CODEC.analog-stereo>
name: <alsa_output.0.analog-stereo.monitor>

Note the name of your input, mine was alsa_input.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00-CODEC.analog-stereo.

Now comes the time to try stuff out, start by recording some sound from the chromecast:

parec -d <YOUR_DEVICE_NAME> | sox -t raw -r k -sLb 16 -c 2 - test.wav

Transfer the file to your computer and try and play it (you could also hook up some speakers to the raspberry directly and try playing the wav file using mplayer or vlc).

All good? Hopefully. Now comes the transcoding part. Instead of recoding the sound we want to serve it as a http-mp3 stream, I use cvlc for this but there are other alternatives (icecast?):

cvlc -vvv pulse://<YOUR_DEVICE_NAME> --sout "#transcode{vcodec=none,acodec=mp3,ab=320,channels=2}:standard{access=http,dst=}"

If there are no dangerous errors you should be good to go and try and open the stream using the sonos application (desktop) using this URL: http://<IP_TO_RASPBERRY>:8080/sonos.mp3). We are close to success if you hear the chromecast sound...

For the last part I've written a small script to detect start and stop of casting and automatically steer the sonos to the cast. Pay extra close attention to the variables in the beginning.


sonos_host='sonos' # you should set up static ip/or let the router give the same ip each time
this_host='cast2sonos' # ...

volume='15' # default volume
pause_timeout='20' # seconds till it pauses the sonos
noise_level='0.005' # depends on your noise level, mine was very low


main () {
# start the transcoder...
cvlc -q pulse://$pulse_input --sout "#transcode{vcodec=none,acodec=mp3,ab=320,channels=2}:standard{access=http,dst=}" &
sleep 5 # .. and let it settle

# this is the timestamp when we heard sound the last time (initialize it to now)
last_sound=$(date +%s)

while true; do
now=$(date +%s)

# check the max amplitude of the recording sound
amplitude=$(timeout 1 parec -d $pulse_input | sox -t raw -b 16 -e signed -c 2 -r 44100 - -n stat 2>&1 | sed -n 's#^Maximum amplitude:[^0-9]*\([0-9.]*\)$#\1#p')

# the code below:
# if we hear some noise (music?)
# swich over the sonos to the chromecast radio station if NOT we are already listening to it
# if it is silence for a while (so it's not just a pause in a song)
# pause the sonos if the user has not switched to another channel already

echo $amplitude

if [ 1 -eq $(echo "$amplitude > $noise_level" | bc -l) ]; then
echo "noise"
if ! is_our_stuff_playing; then
echo "PLAY!"
play >> /dev/null
echo "silence"
if [ 1 -eq $(echo "$now - $last_sound > $pause_timeout" | bc -l) ]; then
if is_our_stuff_playing; then
echo "PAUSE!"
pause >> /dev/null

sonos () {
local "${@}"
curl -s -X POST -H "SOAPAction: $full_type:1#$action" -d "<?xml version=\"1.0\" encoding=\"utf-8\"?><s:Envelope xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\" s:encodingStyle=\"http://schemas.xmlsoap.org/soap/encoding/\"><s:Body><u:$action xmlns:u=\"$full_type\">$arguments</u:$action></s:Body></s:Envelope>" "http://$sonos_host:1400/MediaRenderer/$service_type/Control"


play () {

# sets the uri to this transcoder
sonos service_type='AVTransport'\

# sets the initial volume
sonos service_type='RenderingControl'\

# play :)
sonos service_type='AVTransport'\

pause() {
# pause
sonos service_type='AVTransport'\

is_our_stuff_playing() {
# check that the station is the same as ours
if sonos service_type='AVTransport' action='GetMediaInfo' arguments='<InstanceID>0</InstanceID>' | grep -v -q $media_uri; then
return 1

# check that we are indeed playing our station
if sonos service_type='AVTransport' action='GetTransportInfo' arguments='<InstanceID>0</InstanceID>' | egrep -v -q "PLAYING|TRANSITIONING"; then
return 2

return 0


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12 replies

I did my best to keep the formatting and the code intact.
Hats off to the hackers! Wish I still had the time and inclination...
Video showing the delay when you first start casting:

Here is an image of the mess! :)

In that case why bother?:-)

All this to get Apple music cast from my phone instead of directly via the Sonos controller app???
Userlevel 7
Badge +17
Well done matey, maybe sonos should give you a job 🆒
Chromecast to PLAY1, that I might buy.
Have you tried the multi room function on Chromecast with non Sonos speakers? Any issues with syncing?
NuLevel, I don't have more than one speaker and I don't know the details of the multiroom functionality but I would assume it's on the "sonos side" and thus it should be agnostic where the sound actually comes from.
Userlevel 7
Badge +17
My chromecasts sycn ok when I tested it, not that I group them much, who wants music in empty rooms ;0)
Each chromecast has a sycn delay setting you can set as well.
Oh, I missread your question NuLevel, sorry. No I haven't tested googles multiroom support.
Hi, you wrote that I need a "chromecast audio (I would recommend getting a normal chromecast and extract the audio - the one I got has some limitations)", but what do you mean with "normal chromecast and extract the audio"?
That it works also with chromecast video? If it is, how can I extract the audio?
Thank you in advance.
I used a Chromecast video for avoid Chromecast audio limitations (eg: Spotify doen't work on chromecast audio without a premium account).
I used an HDMI audio extractor to extract audio from the HDMI: https://www.amazon.it/gp/product/B01MRMQM7O/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
I didn't use the script for auto play/pause sonos when some noise was recorded from Chromecase because I have two sonos speakers and I want to be free to decide on which one I want to play sound (or two together, why not?).
So, for do this, I used the Sonos dekstop application to add my streaming as a web radio. After that, when I send video or audio to chromecast and I listen to that web radio (that I called "Cast2Sonos"), I can hear Spotify audio, YouTube audio, Facebook videos audio, etc.
I also created a service on raspberry pi that autostart pulseaudio and create the cvlc streaming.