I stream 4K MKVs from my phone (an iPhone) to my Apple TV 4K using AirPlay all the time. It used to be a challenge getting the codecs right, but there's broader support now. It took awhile to find a good iOS app that supports this, but once I found nPlayer[0] I've never gone back. It's faarrr better than the VLC iOS app.
It works quite well even when my phone is streaming media that's on cloud storage somewhere (nPlayer supports many). But for optimal playback I download the file to my device first.
Of course if you want Dolby Atmos sound, I think you're out of luck. I think HDR should work but not sure.
edit: You can also install app on the ATV that accesses files stored over the network/internet as well, like VLC for ATV. Though I've never found a great one.
App to access files over the network. I think Infuse is pretty good. It supports NAS and if your files are well named then pulls in meta/artwork. Can also be a front-end for Ember/Jellyfin/Plex, but for my LAN media I’m currently going with DLNA.
I use nPlayer to access my files over the network/sftp/Dropbox/WebDAV/put.io/HTTP and download to my local device. But like I said, streaming directly from the network works too. But for a high bitrate 4k file downloading first is better since the server=>phone=>ATV transfer can be too slow. (Resolution doesn’t matter, it’s all about bitrate. Some 4k HEVCs are lower bitrate/smaller files than 1080p h264s)
It works quite well even when my phone is streaming media that's on cloud storage somewhere (nPlayer supports many). But for optimal playback I download the file to my device first.
Of course if you want Dolby Atmos sound, I think you're out of luck. I think HDR should work but not sure.
[0] https://apps.apple.com/us/app/nplayer-plus/id539397400#?plat...
edit: You can also install app on the ATV that accesses files stored over the network/internet as well, like VLC for ATV. Though I've never found a great one.