CSI Cameras
A CSI camera connects to the board with a ribbon cable. pi-webrtc reads it with libcamera on a Raspberry Pi, and with libargus on a Jetson.
Raspberry Pi (libcamera)
Use --camera=libcamera:<id>. The first camera is 0. A Pi 5 with two cameras also has 1.
./pi-webrtc --camera=libcamera:0 --width=1280 --height=720 --fps=30 ...Keep the default camera_auto_detect=1 in /boot/firmware/config.txt. List the cameras with:
rpicam-hello --list-camerasThe image controls, such as --awb, --ev and autofocus, work like in rpicam-apps. See Image controls.
Jetson (libargus)
Use --camera=libargus:<id>:
./pi-webrtc --camera=libargus:0 --width=1920 --height=1080 --fps=30 --hw-accel ...The frames stay in GPU memory. The encoder reads them there, without a copy through the CPU.
Sub-stream
A CSI camera can also give a second, smaller stream at the same time, on both a Raspberry Pi and a Jetson. For example, you can record at full size and stream a smaller copy:
./pi-webrtc --camera=libcamera:0 --width=1280 --height=720 \
--sub-width=640 --sub-height=360 --webrtc-source=sub --record-source=main ...See Sub-stream.
Bandwidth limits
A CSI camera sends uncompressed YUV 4:2:0 frames. Each pixel needs 12 bits. So the link to the camera often limits the size and frame rate, not the sensor.
Each MIPI lane carries 1.5 Gbps on the Pi 5 and 1 Gbps on older models [ref]:
| Interface | 1-lane MIPI (older Pi) | 2-lane MIPI (Pi 4) | 4-lane MIPI (Pi 5) | USB 2.0 | USB 3.0 |
|---|---|---|---|---|---|
| Bandwidth | 1 Gbps | 2 Gbps | 6 Gbps | 0.48 Gbps | 5 Gbps |
For example, 4K at 60 fps needs 3840 × 2160 × 60 × 12 bits per second, which is 5.56 Gbps:
| Resolution | 4K, 60 fps | 4K, 30 fps | 1080p, 60 fps | 1080p, 30 fps |
|---|---|---|---|---|
| Bandwidth | 5.56 Gbps | 2.78 Gbps | 1.39 Gbps | 0.70 Gbps |