Using v4l2 dma hardware encoder with WebRTC reduces CPU usage. Both signalr and mqtt are the options for signaling in this project.

• RaspberryPi 3B + Raspberry Pi Camera v1.3
• RaspberryPi OS 64bit
• clang 12+
• boringssl replace openssl

• Latency is about 0.2 seconds delay.
• Temperatures up to 60~65°C.
• Using HW DMA sources minimizes CPU usage and latency down to ~50ms.

1. Follow SETUP_ARM64_ENV to prepare an arm64 env for compilation (Optional)
2. Follow BUILD_WEBRTC to compile libwebrtc.a
3. Choose a signaling mechanisum
   • Follow BUILD_SIGNALR_CLIENT_CPP to compile microsoft-signalr
   • Follow BUILD_MOSQUITTO to compile mosquitto
4. Install the needed packages on pi

   sudo apt install libboost-program-options-dev libavformat-dev libavcodec-dev libavutil-dev libswscale-dev libpulse-dev libasound2-dev libx11-dev

5. Copy the nlohmann/json.hpp to /usr/local/include
6. Run signaling server
   • Create a signalr server hub on .net
   • Follow SETUP_MOSQUITTO

Build on raspberry pi and it'll output a pi_webrtc file in /build.

mkdir build
cd build
cmake .. -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DUSE_MQTT_SIGNALING=ON
make -j

Run pi_webrtc to start the service.

• If use signalr as signaling.

  ./pi_webrtc --device=/dev/video0 --fps=30 --width=1280 --height=720 --v4l2_format=mjpeg --signaling_url=http://localhost:6080/SignalingServer --enable_v4l2_dma

• If use mosquitto mqtt as signaling.

  ./pi_webrtc --device=/dev/video0 --fps=30 --width=1280 --height=720 --v4l2_format=mjpeg --mqtt_host=127.0.0.1 --mqtt_port=1883 --mqtt_username=<username> --mqtt_password=<password>  --enable_v4l2_dma

• ./pi_webrtc -h to list all available args.
• If --enable_v4l2_dma is assigned, only H264 stream is provided. The VP8, VP9 are available as well if not be assigned. But frames will be decoded/scaled by software, and the buffer will be copied to the HW encoder though.
• If the --record_path is assigned, the background recorder will start immediately after running the program. But the performance of Pi 3B is limited, if the resolution is above 640x368@15fps the HW encoder will be unstable, stuck, or even crash.

Set pi_webrtc to run as a daemon.

• Create /etc/systemd/system/webrtc.service, config sample:

  [Unit]
  Description= the webrtc service need signaling server first
  After=systemd-networkd.service farmer-api.service
  
  [Service]
  Type=simple
  WorkingDirectory=/home/pi/IoT/RaspberryPi_WebRTC/build
  ExecStartPre=/bin/sleep 60
  ExecStart=/home/pi/IoT/RaspberryPi_WebRTC/build/pi_webrtc --fps=30 --width=1280 --height=720 --v4l2_format=h264 --enable_v4l2_dma --mqtt_username=hakunamatata --mqtt_password=wonderful --record_path=/home/pi/video/
  Restart=always
  RestartSec=20
    
  [Install]
  WantedBy=multi-user.target

• Enable and run the service

  sudo systemctl enable webrtc.service
  sudo systemctl start webrtc.service

If the cellular network is used, the coturn is required because the 5G NAT setting by ISP may block p2p.

1. Install

   sudo apt update
   sudo apt install coturn
   sudo systemctl stop coturn.service

2. Edit config sudo nano /etc/turnserver.conf, uncomment or modify below options

   listening-port=3478
   listening-ip=192.168.x.x
   relay-ip=192.168.x.x
   external-ip=174.127.x.x/192.168.x.x
   #verbose
   lt-cred-mech
   user=webrtc:webrtc
   realm=greenhouse
   no-tls
   no-dtls
   syslog
   no-cli

3. Set the port 3478 forwarding on the router
4. Start the service, sudo systemctl start coturn.service

• Version | WebRTC
• Building old revisions | WebRTC
• Using a custom clang binary | WebRTC
• Trickle ICE