Play Cam video on Pi via projector

Posted Aug 16, 2025

By phruit

4 min read

Goal

Set up a 2×2 video wall using the Raspberry Pi, connected to a projector via HDMI, and then project it onto the wall. The easiest path on a Pi is to let FFmpeg tile the 4 RTSP feeds, and pipe to mpv.

Test on PC first

Use mpv (ffmpeg → mpv)

Quick test:

  
mpv --no-audio --profile=low-latency \
    --demuxer-lavf-o=rtsp_transport=tcp \
    rtsp://admin:PASS@Cam_IP:554/Streaming/Channels/102

2×2 video wall:

  
ffmpeg -fflags nobuffer -flags low_delay -rtsp_transport tcp \
 -i "rtsp://admin:PASS@CAM1_IP/Streaming/Channels/102" \
 -i "rtsp://admin:PASS@CAM2_IP/Streaming/Channels/102" \
 -i "rtsp://admin:PASS@CAM3_IP/Streaming/Channels/102" \
 -i "rtsp://admin:PASS@CAM4_IP/Streaming/Channels/102" \
 -filter_complex "[0:v]scale=960:540[v0];[1:v]scale=960:540[v1];[2:v]scale=960:540[v2];[3:v]scale=960:540[v3];\
 [v0][v1][v2][v3]xstack=inputs=4:layout=0_0|960_0|0_540|960_540,format=yuv420p" \
 -f matroska - | mpv --no-audio --fullscreen -

Performance Setting

Pi 4/5 is fine with 4× 720p H.264; 4× H.265 may choke. If needed, drop each scale to 640:360.
Prefer wired Ethernet; Wi-Fi + 4 RTSP feeds can stutter.

Shell Function

  
nvrsub() {
  ffmpeg -hide_banner -loglevel warning -rtsp_transport tcp \
    -thread_queue_size 512 -i "rtsp://admin:PASS@CAM1_IP:554/Streaming/Channels/102" \
    -thread_queue_size 512 -i "rtsp://admin:PASS@CAM2_IP:554/Streaming/Channels/102" \
    -thread_queue_size 512 -i "rtsp://admin:PASS@CAM3_IP:554/Streaming/Channels/102" \
    -thread_queue_size 512 -i "rtsp://admin:PASS@CAM4_IP:554/Streaming/Channels/102" \
    -filter_complex "[0:v]scale=640:360[v0];[1:v]scale=640:360[v1];[2:v]scale=640:360[v2];[3:v]scale=640:360[v3];\
[v0][v1][v2][v3]xstack=inputs=4:layout=0_0|640_0|0_360|640_360,format=yuv420p" \
    -f matroska - | mpv --no-audio --fullscreen --profile=low-latency --hwdec=auto-safe -
}

Save and reload: source ~/.zshrc.

Use:

nvrsub

Hands on Raspberry Pi

Install on Raspberry Pi OS (Bookworm/Bullseye)

  
sudo apt update
sudo apt install ffmpeg mpv

Extra niceties:

  
sudo apt install libavcodec-extra      # widest codec set
sudo apt install fonts-dejavu-core     # if you'll use drawtext labels

Test GUI on Pi by SSH

SSH X11 forwarding: run the app on the Pi, window pops up on PC.

Fast path (works on Linux PC)

SSH to Pi:

  
sudo apt update
sudo apt install xauth x11-apps   # xeyes/xclock for testing
# (optional) sudo apt install mesa-utils  # glxinfo/glxgears tests

Make sure SSH allows X11:

sudo nano /etc/ssh/sshd_config

Set (or add):

X11Forwarding yes
X11UseLocalhost yes

Then:

sudo systemctl restart ssh

Open another session, from PC → Pi:

  
ssh -X -C pi@<pi-ip>    # try -Y if some apps complain
echo $DISPLAY           # should print something like: localhost:10.0
xeyes &                 # or xclock/xcalc - a window should appear on your PC

Now launch any Pi GUI app the same way (from that SSH session).

Tip: X11 forwarding is okay for light GUIs. Don’t try video playback this way; use ffmpeg/mpv pipeline instead.

That little eyeball is xeyes. It’s a tiny X11 demo that follows your mouse, and it proves X11 forwarding is working: the app is running on the Pi, but the window is drawn on your PC.

The & just runs it in the background so your shell prompt comes back.
- See it with jobs
- Bring it back: fg %1
- Kill it: kill %1 (or just close the window)

Use X11 forwarding for light GUIs

From your existing ssh -X or -Y session, try:

xclock &
xcalc &
nm-connection-editor &   # edit Wi-Fi/Ethernet (Pi OS Bookworm uses NM)

Good for config tools and simple apps. But don’t stream video this way.

After this test, just exit the ssh -X -C session.

Launch GUI on the Pi’s projector from your PC

That will pop the 2×2 mosaic on the projector (not PC).

Interactive (ssh first → then run GUI there)

From PC:

 ssh pi@PI_IP

Now you’re inside the Pi’s shell (prompt shows something like pi@raspberry). Re-do this step first -> shell function. Then:

  
 # 1 Grant once per boot - this edits the Pi's display permissions
 DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority xhost +SI:localuser:pi
 # 2 Launch a test GUI ON THE PI'S SCREEN
 DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority xeyes &
 # 3 Launch your camera wall ON THE PI'S SCREEN
 DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority nvrsub

Make the grant automatic (systemd user unit)

From your PC (one shot to install on the Pi):

 ssh pi@PI_IP 'mkdir -p ~/.config/systemd/user && cat > ~/.config/systemd/user/xhost-localuser.service <<EOF
 [Unit]
 Description=Allow local SSH user to access X/XWayland
 After=graphical-session.target
 PartOf=graphical-session.target

 [Service]
 Type=oneshot
 Environment=DISPLAY=:0
 Environment=XAUTHORITY=/home/pi/.Xauthority
 ExecStart=/usr/bin/xhost +SI:localuser:pi

 [Install]
 WantedBy=graphical-session.target
 EOF
 systemctl --user daemon-reload
 systemctl --user enable --now xhost-localuser.service'

Now each time the Pi’s desktop starts, the permission is granted.

Then, whenever you want to launch stuff (interactive):

  
 ssh pi@PI_IP
 DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority xeyes &
 DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority nvrsub

Or as a one-liner from another device (quotes keep it on the remote side):

 ssh pi@PI_IP \
 'DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority nvrsub'

Alias (optional)

Add this alias to Pi’s ~/.bashrc:

  
# draw GUI on the Pi's local screen from SSH
alias onpi='DISPLAY=:0 XAUTHORITY=/home/pi/.Xauthority '

Reload:

source ~/.bashrc
type onpi