So, I have a StarTech dock which means I can extend my displays on the Mac to 3 HP screens. The minute I've tried to watch Netflix et al, via the external monitor (and the Mac screen too), the sounds is ok but no picture?
[Re-Titled by Moderator]
MacBook Air 13″, macOS 15.1
Your tag line says that you are using a 13" MacBook Air running macOS 15.1 (Sequoia).
You say that you are extending your displays "to 3 HP screens." None of the MacBook Airs that are compatible with Sequoia support three external displays, and many support only one. That tells us that the dock you are using relies on some sort of "stunt box" workaround – using DisplayLink or something like it.
These workarounds, which involve installing special software drivers on your Mac, often do not play well with DRM-infested video from commercial movie and TV streaming services. The streaming services see that the path to the display, through your own hardware and software, is not completely locked down against you. The DRM treats you as if you were a pirate, and intentionally cuts off the video.
For instance, if you are using adapters or hubs with the DisplayLink workaround, "as soon as one DisplayLink screen is connected, protected content becomes unavailable on all screens." (Reference: DisplayLink – Content protected video does not play on Mac while DisplayLink screens are connected). I expect the behavior would be pretty much the same with other workaround technologies.
Your tag line says that you are using a 13" MacBook Air running macOS 15.1 (Sequoia).
You say that you are extending your displays "to 3 HP screens." None of the MacBook Airs that are compatible with Sequoia support three external displays, and many support only one. That tells us that the dock you are using relies on some sort of "stunt box" workaround – using DisplayLink or something like it.
These workarounds, which involve installing special software drivers on your Mac, often do not play well with DRM-infested video from commercial movie and TV streaming services. The streaming services see that the path to the display, through your own hardware and software, is not completely locked down against you. The DRM treats you as if you were a pirate, and intentionally cuts off the video.
For instance, if you are using adapters or hubs with the DisplayLink workaround, "as soon as one DisplayLink screen is connected, protected content becomes unavailable on all screens." (Reference: DisplayLink – Content protected video does not play on Mac while DisplayLink screens are connected). I expect the behavior would be pretty much the same with other workaround technologies.
So the external monitors work fine otherwise when displaying computer windows on the three monitors?
If so, SERVANT of CATS is likely right.
There is a chance your cables are not fit for the bandwidth but that is more remote.
Try just using two external monitors and not three and see what happens.
If that does not work, try just using one external monitor to see what happens.
Netflix, Amazon, Apple TV+ streaming issues on MacBook Air with external monitors
