Apple TV 4K keeps buffering when I watch certain chains on IPTV

My initial thought was insufficient bandwidth on the content provider's side... But your statement of the Mac's performance with the same content seems to dismiss that.

I've seen a few reports on this forum of Ethernet-connected ATV4Ks making very poor use of the available Internet bandwidth. As a troubleshooting step, try disconnecting the cable and using a WiFi connection instead. I can imagine that the QA process at Apple is heavier on the (much more commonly used) WiFi connections.

Apparently the latest ATV4K models include a WiFi-only unit and a more expensive unit with an Ethernet port. Hopefully that added-cost port is really fast! It's also possible that your home Wifi hub/router has those "100GB" ethernet ports but the device is totally optimized for WiFi.

Hi pierfconsa,

The guidance below can help resolve issues related to Apple TV playback quality:

"If the movie or TV show won't start playing

After each step, try to stream or download the movie or TV show again.

1. Check the System Status page for service interruptions or check a third-party provider's website for any interruptions. If there are service interruptions, try to stream or watch the video later.
2. If you're having trouble signing in with your Apple ID, you can reset your Apple ID password or learn how to get a verification code and sign in with two-factor authentication.
3. If your cellular connection is poor, connect to Wi-Fi instead.*
4. Try watching on a different device using the same Wi-Fi or cellular connection. If it doesn't work, contact your internet service provider to see if there's an issue with your network.
5. If other people are using Apple TV+ or Apple TV channels, make sure it doesn't exceed the limits for streaming on multiple devices.

* Make sure that your Wi-Fi router is 802.11a/g/n/ac compatible. Streaming HD content requires 8 Mbit/s or faster. Slower tiers of Wi-Fi connections might not be fast enough to stream HD video content.

If the video quality is bad or it stops playing

1. If multiple people on your network are using the internet, your connection speed might slow down. Ask them to temporarily pause their internet activities.
2. If you're using a smart TV or streaming device, turn it off and back on again. If you're using an Apple device, restart it.
3. Tap or click the download button to try downloading the movie or TV show instead.*

* You can't download movies or TV shows to Apple TV, smart TVs, or streaming devices. You can download HDR content only to certain iPhone, iPad, and iPod touch models. You can't download 4K video content to any device.

Still need help?

If you still can't play movies or TV shows, you can go to reportaproblem.apple.com and request a refund.

If you can't stream movies or TV shows in apps that you downloaded from the App Store, you can contact the app developer.

"

If you can't watch or stream movies and TV shows in the Apple TV app - Apple Support

Cheers.