Let's discuss HDCP and the 2 common computer types that interface with AV systems, PCs with Windows and Apple Macs. There are subtle differences how each react, and the manner with which each company has decided to handle connections to an HDCP-capable sink device. There are pros and cons with both however, understanding the differences will help to troubleshoot commercial AV installations. If there are any terms you may be unfamiliar with, please check out the AVPro Edge AV Glossary
First up: PCs and Windows
When you connect a Windows machine to a sink device, it will perform the HDMI negotiation and begin playing content. What about HDCP? Even if the sink is HDCP enabled, the PC will not send an HDCP encrypted video stream. In fact, it will wait until you attempt to play protected content. When protected content is ready to play, HDCP will attempt to re-negotiate and encrypt the content. If the sink device is not HDCP capable, the PC outputs a black screen. If the sink is HDCP capable, it will send the content via an encrypted stream which sink devices can decode and display. This process is no different than what you would expect from a Blu-Ray player or other media devices (though it may vary depending on manufacturer and model).
There are good things about this approach, mainly a guarantee unencrypted content will display when users connect devices. This limits a potential for failure, especially in distributed systems where HDCP may not be available at all endpoints. This is the "just make it work" approach.
The downside with this approach is you may have, then lose, an image making it harder to troubleshoot, as it may not be easy to identify this as an HDCP issue, especially since there was an image present at one point in time. Additionally, it is not easily known what programs, websites, etc. may be requesting HDCP playback.
Next up: Apple Mac computers
Apple takes a slightly different viewpoint on the HDCP challenge. Rather than wait until protected content is playing, the Mac negotiates with the sink device and if the sink reports back as HDCP compliant the Mac establishes an HDCP encrypted stream immediately. That's it, either HDCP or no HDCP. Pretty simple to think about!
Apple uses a slightly different approach with HDCP. Rather than waiting until protected content is playing, a Mac computer negotiates with a sink device and if it is determined the sink is HDCP compliant, Mac immediately initiates an HDCP-encrypted stream. Apple's Mac makes it simple: HDCP or no HDCP.
The benefit to the Apple approach is simplified troubleshooting plus an ability to identify HDCP problems. The signal does not change or become encrypted, which you are then forced into identifying and monitoring.
However, a downfall to the all-or-nothing approach in distributed systems are sink devices that follow a distribution system or a device functioning as a repeater may not support HDCP. One example is conference rooms, where most applications include video conferencing with either Cisco / Poly or Zoom / Teams. The content inputs on these codecs are typically not HDCP compliant. When a Mac is connected directly or its input is routed to the codec in a conference room, it does not attempt to renegotiate with the codec. And since the codec is non-HDCP compliant, a Mac will subsequently output a black / blank stream.
How to manage Windows and Mac devices in a distributed system:
Now that the pros and cons of each approach are understood, I'm sure you can picture various scenarios where end-users may have challenges displaying content in distributed systems. There are two primary recommendations for overcoming these issues:
1. Disable HDCP on input sink devices. If you are using a wall plate for signal input or extension with a distributed system, disable HDCP support on the input. This forces Apple Mac computers into a non-HDCP stream, while for Windows PCs, they are prevented from switching over.
2. Require system designs to account for HDCP compliance with every device. This may not be feasible or entirely possible, depending on
customer requirements but it will provide the richest experience for end-users without compromising playback options.