In addition to the answers above, you can't try using an Apple AirPlay sender app for Android in conjunction with Shairport-sync, which is available from this PPA. Just do
sudo add-apt-repository ppa:dantheperson/shairplay-sync
sudo apt-get update
sudo apt-get install shairport-sync
to install it. I personally have not tried it out, tu it looks promising. If you just want to cast from the YouTube app or Google Play Music, there are a few older Google Cast receivers you can try. For instance, if you have Chromium or a derivative you can try CR Cast, which while no longer on the Chrome Web Store, still works happily on my Raspberry Pi. You will need to download as a zip and lad in the extension manually though. You can also try Nodecast which runs on NodeJS. You'll need to run it as root for it to work right. Just note that the previous two options don't support full screen mirroring, just YouTube.