Adding Display

In automation scenarios, the Raspberry Pi is typically managed remotely via Web Interfaces and the browser. There are valid reasons though why it makes sense to hook up the local HDMI outputs, too.

Overview

Like any other computer, the Raspberry Pi has Micro HDMI connectors for up to two computer displays. This way, you can work locally (directly) with the Raspberry and see its direct output. Here are some reasons why you would want to do this:

• Use As Regular Computer: Raspberry Pi is a full-fledged computer and can run Debian distributions or even a graphical user interface. If you want to use it this way, you need displays.
• Bug Fixing: A Web Interface requires that you can actually connect to the Raspberry. If you need to know its currently assigned IP address in order to connect, or if anything else is amiss, a display helps because it does not rely on remote connections.
• Advanced Configuration: most fundamental configuration tasks (i.e. setting or changing the boot loader order) can only be done locally, in which case you need a display and a USB keyboard.

Regular Computer Display

If you opt to connect a regular computer display, then there is not much special to know. All you need is a Micro USB HDMI cable, or better yet two of them for both Micro HDMI connectors.

Plug the Micro HDMI end of it into one of the Raspberry Pi HDMI connectors, and the other end with the regular-sized HDMI plug into any computer display or TV set of your choice.

Using a HDMI Switch Box is the simplest option: when needed, simply switch the Raspberry HDMI output to your regular computer display.

Virtual Displays

If you need the Raspberry Pi Display only occasionally, or you want to keep an eye on it while working with your normal computer, then get a simple USB HDMI Grabber.

Connect the HDMI cable to the Grabber connector, and plug in the USB adapter into your computer. Use an adapter plug to convert USB-C and USB-A when needed.

The grabber needs to be connected to a high speed USB port. Typically it suffices to plug it directly into one of the computer USB ports. If you use external USB switches, some are low quality: when the grabber is plugged in here, it will be discovered and installed but does not produce a picture.

Now you just need software to show the screen output delivered by the USB HDMI Grabber. There are a couple of free options that work well.

OBS Studio

OBS Studio is an open-source streaming and recording solution available for Windows, macOS, and Linux.

After download and install, the software asks whether you record only or also plan to stream. Choose record only (unless you do want to use *OBS** for other purposes, too).

Next, add a new video source, and choose Video Capture Device:

A dialog opens. Choose Create new, and assign a name to it:

Once you choose your USB HDMI Grabber in the Device combo box, you already start to see the Raspberry Pi Screen in the upper part. Click OK

By right-clicking into the screen, choose Windowed Projector (Preview). This opens a separate monitor window (a so-called Projector) showing only the Raspberry Pi Screen Cast:

Right-click the OBS icon in the taskbar and Pin it to Taskbar (on Windows) so you can later easily open OBS when you need it.

Strip Down

Since you do not need the feature-packed OBS studio UI, click Settings in its lower right area. This opens the Settings dialog.

Scroll down to the section Projectors, and enable these options:

• Make projectors always on top: makes sure the screen window is never obscured by other windows.
• Save projectors on exit: re-opens all projector windows that were open when you exited OBS. So next time you open OBS, it automatically opens your projector window again. Just make sure there was indeed a projector window open when you exit OBS: never close the projector window when you are done. Always close the OBS Studio window instead.

In the next section System Tray, enable this option:

• Minimize to system tray when started: when you launch OBS, the main studio UI is not visible. Instead, OBS places just an icon into the system tray area of the OS taskbar.

Then click OK.

Test Drive

Make sure you opened a Projector Window as illustrated above, and it is showing the Raspberry Pi Screen.

Now close the OBS studio window (do not close the projector window; it will be closed automatically).

When you now click the pinned OBS icon in your taskbar, OBS starts quietly, and you only get the projector window with the Raspberry Pi screen cast.

VLC Media Player

You can also use the popular VLC Media Player to connect to the USB HDMI grabber.

Before you proceed: VLC has caused significant CPU load in my experiments. It works great to have a quick peek but it is not recommended as a computer display replacement for longer use.

Launch VLC, then choose Media/Open Capture Device. This opens a dialog. In video device name, select the name of the USB HDMI grabber you use, then click Play.

Fixing Low Resolution

VLC immediately displays the Raspberry Pi screen, however the resolution may be extremely poor.

This is the consequence of using a cheap HDMI grabber that is not able to support USB3 standards (even if it claims to):

To fix this, go back to Media/Open Capture Device, and check Show more options. At the bottom, you now see a textbox labeled Edit Options with default options: ` :dshow-vdev=USB2 Video :dshow-adev= :live-caching=300`.

Add these options to the end of the line, and click Play:

:dshow-chroma=MJPG  :dshow-aspect-ratio=16:9

Now the display looks good and is using the original resolution and aspect ratio.

Creating Shortcut

You can launch VLC with all required setting via this command line:

"C:\Program Files\VideoLAN\VLC\vlc.exe" dshow://  ":dshow-vdev=USB3 Video" :dshow-adev=  :live-caching=300 :dshow-chroma=MJPG  :dshow-aspect-ratio=16:9

Make sure you adjust the path where you store vlc.exe. Also make sure to change the video source name from USB3 Video to whatever name your grabber uses. Important: this setting must be quoted if the grabber name contains spaces or other special characters.

When using VLC this way, unfortunately you may now hear your computer fan spin up frequently. Task manager reveals: VLC is hogging one CPU core. It’s ok to have an occasional peek at the Raspberry Pi screen but won’t work well for continuous use. This is the downside of using the MJPEG mode. Using a grabber with better hardware acceleration can fix this. Or use the OBS Studio solution shown first. It handles the video processing superbly without noticeable strain on the CPU.

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