I use infuse on an ATV4k to stream 4K MKV files off my 2013 MacBook Air. My air is connected to my Apple TV via an Ethernet cable but video still freezes to buffer. Any idea why? Settings says the Ethernet is connected and my laptop is even connected to my network via Ethernet. Everything is hardwired but I still get lag/buffer.
Welcome to the forum!
On your MacBook Air, are you using a USB2 or Lightning Ethernet adapter? Apple’s USB2 adapter is actually limited to 100Mbs, so you may in fact be able to get faster speeds by connecting via Wi-Fi. The Thunderbolt adapter will support 1Gbs.
One other thing you may try is adjusting the SMB version as described here.