Currently, we do not support using both HDMI ports on the Xandadeck 4K Player (Raspberry Pi 4). Why?
If you wanted to always show identical content on two screens, then you can always use a $5 HDMI splitter. This way, you can even drive more screens, using larger 1-to-10 HDMI splitters. The real question is for driving 2 screens with different content on each. The latest version of our hardware platform, the Raspberry Pi 4, provides two micro-HDMI ports for connecting two screens. However, the hardware has several restrictions when it comes to supporting a dual-screen setup. Here are the most important ones.
- Dual 4K screen setup is limited to a refresh rate of 30Hz.
Normally, a refresh rate of 60Hz is supported for 4K screens, but adding a second screen limits output to 30Hz. While this is not a significant restriction, it does affect playback quality.
- There is only 1 hardware decoder for video, making it difficult to show two different videos on the two screens.
Actually, there is 1 hardware decoder for video encoded in the H.265 format (supporting up to 4K video) and 1 hardware decoder for video encoded in the H.264 format (supporting up to 1080p video). However, this means that we need to have videos in multiple formats, just to allow playback of different videos on the two screens.
- The Player cannot turn both screens on and off.
The Player uses the HDMI-CEC protocol for turning screens on and off. Unfortunately, CEC support is only provided for the primary screen, so the second screen cannot be turned off and on based on a schedule.
- The hardware cannot handle Layouts on two screens, especially if one is running at 4K.
The Player has a hardware component called “compositor”. The compositor takes the different layered content (e.g. video, overlayed images, RSS tickers, etc) and combines them in a single output. If the compositor is overloaded, then the output turns black. And this is out of our control. Currently, the compositor may be overloaded at 4K even with a single screen.
Besides the hardware restrictions, building support for dual screens also has several implications on the software side. And not all of our users are tech-savvy; we have HR and marketing departments purchasing Xandadeck, and we cannot explain all the above restrictions in a clear way during their (short) evaluation of what we provide. It is much better to leave out the dual-screen option and keep it simple for everyone.
For special projects over 1000 units that might need dual screen support, we can investigate it as special customization. As a mainstream feature for all customers, dual-screen support is not a priority right now. We might provide it down the road, but not in the near future.
If you have any questions, do not hesitate to contact our support team.