I'm a huge AV nerd and I borrowed a pair of AirPods Pro from a friend to test out the Spatial Audio feature, and I see there's a lot of ambiguity regarding this feature and a lot of misinformation and these are my findings after thorough testing:

Firstly, the technology behind this is fascinating. It uses math and HRTFs to map audio frequencies as if they were around you, along with the extra mile Apple goes to have dynamic data by tracking your head movement through the sensors on the AirPods.

Secondly, content support: Right now it’s super limited, only Apple TV content mixed in 7.1 and 5.1 or Dolby Atmos works.

What iOS looks for is atleast a 5.1 track output, in Dolby Digital or Digital to trigger the Spatial Audio feature hence, AAC won't work, and music won’t work by default.

And the only apps which output 5.1 audio are AppleTV and Disney You can try Tidal if it’s available in your country since that supports Dolby Atmos music, I tried listening to some Shawn Mendes and Ariana Grande on my OnePlus device when I had a subscription but it sounded terrible, music doesn’t work that well with any virtual surround sound tech.

Secondly if you want to watch locally downloaded content, you need to play it back through the built-in QuickTime Player, Infuse doesn’t support Spatial audio yet, and those files need to be 5.1, AC3 in an mp4 container. I have custom converted and muxed some trailers and i'll try linking those below. Just download and Save to Files app and you'll be golden.

If you are willing to shell out money on Apple TV rentals, try out Gravity and Mission Impossible Rogue Nation, excellent Atmos mixes with great overhead activity.

In Gravity, around the 42 minute mark, the alarm sound has a great overhead effect. In M:I-5, around the 50 minute mark, the helicopter blades also provide an excellent spatial effect.

Also PSA: Do not download or try out “3D Audio” or Dolby Atmos sample videos on YouTube, they're mixed and exported as binaural audio, and will work on any pairs of headphones. The specialty of Spatial Audio is that it converts normal 5.1 and 7.1 tracks to Binaural Audio on the fly.

That’s it, Reddit is the only place where I can talk about niche things, hopefully somebody cares lol

EDIT: THANKS FOR THE AWARDS, STRANGERS!

My YouTube video: https://youtu.be/nAJyVorZFxQ

Samples: https://drive.google.com/drive/mobile/folders/1-3kiX97nUJE0t8yzgT4rWbXgbaR_zROp?usp=sharing

Also my YouTube video was mastered in 5.1 Atmos, and the raw file is in the drive link itself, you can get an idea of how a YouTube video should sound through it :)