The Amp is on it's first generation, though Sonos has produced products like it before. Sonos does not do Chromecast, which is Google's equivalent to Apple's Airplay. If your girlfriend wants to use Youtube Video for music, you need to hook up a TV to the Amp. Youtube Music is supported in the Sonos app.

Sonos must has thought of this (and you are not the first one telling them he misses it), but Sonos has not implemented it. 

It’s actually, I believe, up to Google to make this available. Given the ongoing legal battles between the two companies, it seems unlikely that Google will allow it. Google certainly haven’t so far, and there are years of requests for it here in these forums. 

I don’t know if it holds true any more, but my understanding is that google does not allow casting of youtube to device that don’t carry video.  The thought was that the content and ads required video to be seen as the content producers intended.  It does make some sense when you consider that companies for ads based on views want them to actually be viewed.  So anyway, even if chromecast was supported, I’m not sure that youtube videos would be.

Also worth noting that you can get a Sonos speaker that is bluetooth compatible (Roam, Move, Era 100, Era 300) and it can group it share that bluetooth audio with your amp.  Alternatively, you can get a bluetooth receiver dongle and attach it to the aux input  on the amp.

There is the rumoured new app coming soon; who knows what features and facilities might be introduced with that…

Anything involving additional features from Google, I’m skeptical about, given the antipathy between the two companies. 

Well it’s also a matter of definition.   Airplay is doing it.  And sonostube does it.  

All it would require is for the app, to make the phono reconize a new sound source like (cable, wireless headphones etc.)  which is pretty simple.  once the phone is directing it’s sound signal to that new source.   that source can then be transferede via the wifi transmistion.

so it ONLY at matter of “do we want to” at sonos’ end

Hmm. Sonos needs Airplay to do this from an iPhone, so it seems they can’t do it themselves. Why should they be able to doe this from an Android phone? Especially since Sonostube seems not to be able to do it from (paid) video sources.

Isn’t it as much a ‘we’ll sue you if you implement our code’?

Airplay is doing it because Sonos pays for Apple Airplay licensing.  A similar arrangement would be required with Google, who isn’t in the best relationship with Sonos right now.  As far as Sonostube goes, that’s an independent app developer coding away in their basement.  Airplay had the same, and Apple would occasionally shut them down, but small fish seldom get much attention.  Sonos has far deeper pockets than that, and Google’s lawyers would be on them faster than you can say “I hacked Chromecast”.

That’s a more polite way of saying ‘you don’t have a license to implement our code’ than perhaps my other post. ;)