I've been trying to watch videos using my old Sonos speakers for years without success: I kept getting sound delays or had to go through unreliable, convoluted tweaks. Until I found out about this trick that allowed me to use room filling digital audio for movies, using my existing Sonos setup, in perfect sync.



It prevented me from having to invest in yet another expensive sound bar for movies, while perfectly fine Sonos setup was around in my living room. The solution does not involve the Play:5 line-in, which never was a real option, as it adds an audio delay that ruins image/audio sync.



Anyways, the solutions below is working well for me so far.



Limitations:

• Digital stereo sound only, no surround or 5.1
  
• Need to have at least 1 Sonos AirPlay speaker, if you don't have one already (min 99$).
  
• Your Sonos AirPlay speaker may need to be muted each time you start a movie, if you don't use it for your home cinema.
  

What you'll need:

• Apple TV (4th gen) or Apple TV 4K, with tvOS 13 or later
  
• An iPhone with iOS 13 or later
  
• Sonos speaker(s) you'd like to use with your Apple TV. I used 2x Play:3 in stereo in the front, and 1x Play:5 (1st gen) in the back.
  
• 1x AirPlay compatible Sonos speaker. E.g. Sonos One, or SYMFONISK (cheapest as of today).
  

How to (needs to be done once only)

1. Set up your speakers around your TV as if you'll use them for home cinema. If you put a Play:5 in the back, consider flipping it upside down otherwise stereo will be inverted.
   
2. Set up Wireless Audio Sync: From your Apple TV, go to Settings > Audio Video, Wireless Audio Sync, to synchronize your wireless audio devices to your TV's audio. You need to have tvOS 13 installed, update your Apple TV if you don't see the setting. Follow the steps displayed and use your up-to-date iPhone when asked.
   
3. Set your Sonos speaker as Apple TV output: Go to Settings Video and Audio, select Audio Output, then select the name of your Sonos AirPlay speaker.
   
4. Group your speakers: Open the Sonos app and group your Sonos speakers that you want to use for home cinema with your Sonos AirPlay speaker. Go to Settings > AirPlay, and select the "Group non AirPlay speakers" setting to avoid having to group them again in the future.
   
5. Select the new output in your Apple TV: Long press the TV icon to and select the AirPlay icon, select your Sonos AirPlay speaker name. You may want to deselect your Apple TV as sound output, otherwise will get sound coming out of your TV/projector as well.
   

There you go, you should now be ready to watch Netflix, YouTube, Infuse, VLC, Apple Photos app, and more with image and audio in perfect sync with your Sonos setup. Keep in mind: Menu navigation clicks will still come out of your TV. That is normal, it's to ensure you get feedback in real time.