A small Linux appliance for converting analog RCA audio into HDMI audio plus a fullscreen now-playing display.

The intended hardware path is:

• RCA stereo source
• USB audio interface for capture
• Raspberry Pi or Jetson Nano HDMI output to a TV/projector/capture chain
• Live audio monitor from USB capture input to HDMI audio output
• Shazam-style now-playing recognition for the vinyl feed
• Fullscreen now-playing display with track metadata and progress

This repository contains an installer and systemd units to make the box boot directly into the appliance experience:

• automatic graphical login through LightDM
• fullscreen now-playing display launched on boot
• PipeWire/PulseAudio audio loopback from USB capture to HDMI output
• unattended security upgrades enabled
• unattended upgrade window set to 4:00 AM
• optional Jetson Nano 10W/jetson_clocks performance service
• optional now-playing recognition daemon using a Shazam-style snippet recognizer
• Tailscale installed and tailscaled enabled for manual login/configuration

Recommended options:

• Jetson Nano Developer Kit running official JetPack 4.6.x / L4T Ubuntu 18.04.
• Raspberry Pi OS 64-bit with desktop on a Raspberry Pi 4 or Pi 5.

Raspberry Pi 3 can output 1080p and should be much happier with the lightweight now-playing display than it was with a full audio visualizer.

On a freshly installed supported desktop image:

sudo apt update
sudo apt install -y git

git clone https://github.com/rmkraus/rca-audio-hdmi-visualizer.git
cd rca-audio-hdmi-visualizer
sudo ./scripts/install.sh
sudo reboot

Force a platform if auto-detection is wrong:

sudo ./scripts/install.sh --platform jetson-nano
sudo ./scripts/install.sh --platform raspberry-pi
sudo ./scripts/install.sh --platform generic

Tailscale is installed by the installer, but it is not authenticated automatically. After install, log in manually on the node:

sudo tailscale up

After reboot, the system should log in as the configured desktop user, start the graphical session, show the fullscreen now-playing display, and start audio loopback from the USB audio interface to HDMI.

The Jetson Nano has plenty of headroom for the current now-playing display. Use a proper 5V/4A barrel-jack power supply, cooling, and 10W mode.

The installer adds jetson-performance.service on Jetson Nano. It runs:

nvpmodel -m 0
jetson_clocks

The original Cavasik visualizer is now legacy/optional. The installed boot path does not start a visualizer; it starts the fullscreen now-playing display only.

Recognition is disabled by default. To use it, enable RECOGNITION_ENABLED=true in /etc/rca-hdmi-visualizer.env and restart the recognition services.

sudo nano /etc/rca-hdmi-visualizer.env
sudo systemctl restart rca-now-playing.service rca-now-playing-overlay.service

One-shot test:

sudo rca-now-playing identify-once
jq . /var/lib/rca-hdmi-visualizer/now-playing.json

The default conservative sample length is 12 seconds. See docs/now-playing.md for tuning sample length, polling interval, silence detection, and overlay opacity.

• Use a USB audio interface with stereo line input. Many cheap dongles expose mic input only; those can clip or sum the signal incorrectly.
• RCA output is line-level. If your interface has gain controls, start low and raise until recognition sees healthy RMS without clipping.
• HDMI audio output must be selected as the default output, or explicitly configured in /etc/rca-hdmi-visualizer.env.
• If the RCA source hums, use a USB interface with isolation or add an RCA ground-loop isolator.

The installer creates /etc/rca-hdmi-visualizer.env from config/rca-hdmi-visualizer.env.example.

Useful settings:

• VISUALIZER_USER: desktop user that runs the GUI and user audio session.
• PLATFORM: detected install platform, such as jetson-nano, raspberry-pi, or generic.
• SOURCE_MATCH: case-insensitive text used to identify the USB capture source.
• SINK_MATCH: case-insensitive text used to identify the HDMI output sink.
• LOOPBACK_LATENCY_MSEC: requested PipeWire/PulseAudio loopback latency.
• RECOGNITION_ENABLED: enables/disables now-playing recognition.
• RECOGNITION_SAMPLE_SECONDS: sample length sent to the recognizer; 12 seconds is the default, 15-20 can improve difficult passages.
• RECOGNITION_MIN_RMS: silence gate; samples quieter than this skip lookup.
• OVERLAY_ALPHA: fullscreen overlay opacity.

To inspect audio device names after install:

sudo -u "$USER" pactl list short sources
sudo -u "$USER" pactl list short sinks

Then edit:

sudo nano /etc/rca-hdmi-visualizer.env
sudo systemctl restart rca-audio-loopback.service

System services installed by this repo:

• rca-audio-loopback.service: creates an audio loopback from the selected USB capture source to HDMI output.
• rca-now-playing.service: records short audio samples and identifies them with the Shazam-style recognizer.
• rca-now-playing-overlay.service: shows now-playing metadata in a fullscreen always-on-top display.
• jetson-performance.service: Jetson Nano only; enables 10W mode and max clocks.

Useful commands:

systemctl status rca-audio-loopback.service
systemctl status rca-now-playing.service
systemctl status rca-now-playing-overlay.service
systemctl status jetson-performance.service
journalctl -u rca-audio-loopback.service -f
journalctl -u rca-now-playing.service -f

The installer configures unattended-upgrades and apt timers so package updates run around 4:00 AM.

Files installed:

• /etc/apt/apt.conf.d/20auto-upgrades
• /etc/apt/apt.conf.d/51rca-hdmi-unattended-upgrades
• systemd timer drop-ins for apt-daily.timer and apt-daily-upgrade.timer

Check timers with:

systemctl list-timers 'apt-daily*'

• This setup currently expects X11 because the fullscreen display uses Tk.
• Recognition uses an unofficial Shazam-style recognizer. Keep polling conservative and expect the upstream endpoint/library to change without notice.