Opencast Capture Agent Display

Software backend for displays showing the current state of Opencast capture agents.

How to build your Capture Agent Display

List of components

• Case: https://github.com/virtUOS/opencast-ca-display/tree/3d-printed-case
• Raspberry Pi Compute Module 4: https://www.raspberrypi.com/products/compute-module-4/?variant=raspberry-pi-cm4001000
• Touchscreen: https://www.waveshare.com/7inch-hdmi-lcd-c.htm
• IO Board: https://www.waveshare.com/compute-module-4-poe-board-b.htm
• Miscellaneuos:
  • HDMI Cable: https://www.amazon.de/dp/B07R6CWPH1?th=1
  • USB Cable: https://amazon.de/dp/B095LS6S2Y
  • Ethernet Cable: https://www.amazon.de/ACT-Netzwerkkabel-gewinkelt-Flexibles-Datenzentren-Schwarz/dp/B0CYHG3HV2?th=1 (Alternatively, any other 90° right angled cable can be used)

Instuctions

1. Put Raspberry Pi CM4 on the base board
2. Set the boot switch to on
3. Connect the board via USB-C cable
4. Run rpiboot to mount the CM4 file system
5. Start Raspberry Pi Imager:

• Device: Raspberry Pi 4
• OS: Raspberry Pi OS Lite (64 bit)
• Target: Select the CM4 Module Filesystem
• Additional settings:
  • Enable SSH public key
  • Set default SSH key
  • Disable telemetry

6. Write image to CM
7. Set boot to off
8. Boot Raspberry Pi
9. Run the Ansible playbook prepare-os.yml
10. Get MAC address (e.g. ip a on system)
11. Configure the agent setting in /opt/opencast-ca-display/opencast-ca-display.yml to the corresponding capture agent
12. Reboot the Raspberry Pi

Build & Run

Make sure to install Go. This should be something like:

❯ dnf install golang

Then run the project with:

❯ go run main.go

…or build a static binary:

❯ go build

Example

The display control in action:

opencast-ca-display-prototype.mp4

• The display and laptop do not know about each other
• The laptop is running an Opencast capture agent
• When the laptop starts capturing video, the display shows an active recording

Opencast User

To improve security, you can limit the access rights for the Opencast user by creating a user which has only read access to the capture agent status API and nothing else.

To do this, first create a new security rule in your Opencast's etc/security/mh_default_org.xml allowing read access for a new role ROLE_CAPTURE_AGENT_CALENDAR:

<!-- Enable capture agent updates and ingest -->
<sec:intercept-url pattern="/capture-admin/agents/**" method="GET" access="ROLE_ADMIN, ROLE_CAPTURE_AGENT, ROLE_CAPTURE_AGENT_CALENDAR" />
<sec:intercept-url pattern="/capture-admin/**" access="ROLE_ADMIN, ROLE_CAPTURE_AGENT" />

Next, go to the Opencast REST Docs → /user-utils and fill out the form for POST / with data like this:

• username: ca-display
• password: secret-password
• roles: ["ROLE_CAPTURE_AGENT_CALENDAR"]

You should now be able to use this new user.