Performance

Measure where the delay comes from, and make the device faster.

Measure the delayCopy Anchor Link

--latency-trace measures each frame from the sensor to WebRTC. It prints the median (p50), p95 and maximum time of each step every few seconds. It works in release builds.

./pi-webrtc ... --latency-trace --latency-trace-interval=5

General tipsCopy Anchor Link

• Use --hw-accel. pi-webrtc then uses the hardware decoder, scaler and encoder when the board has them, and moves frames without copies.
• For a USB camera, use mjpeg or h264 instead of an uncompressed format. See USB cameras.
• Ask for the size and frame rate that you need, not the largest one. Check the bandwidth limits of CSI cameras.

Jetson: speed up the VIC and NVENC clocksCopy Anchor Link

On a Jetson, the VIC (image copies) and NVENC (encoding) engines can run at low clock speeds under the default tegra_wmark governor. This can add a lot of delay. jetson_clocks and nvpmodel MAXN do not raise the speed of these engines.

For example, on an Orin NX at 1080p and 60 fps, the performance governor cut the delay on the device from about 36.5 ms to 24 ms in our test.

1. Check the current state:

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   for d in /sys/class/devfreq/*vic* /sys/class/devfreq/*nvenc*; do
       echo "$d: $(cat $d/governor) $(cat $d/cur_freq) / $(cat $d/max_freq)"
   done

2. Use the performance governor until the next boot:

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   echo performance | sudo tee /sys/class/devfreq/15340000.vic/governor
   echo performance | sudo tee /sys/class/devfreq/154c0000.nvenc/governor

Keep it after a rebootCopy Anchor Link

The governor resets at every boot. Create /etc/systemd/system/tegra-mm-perf.service:

[Unit]
Description=Pin Tegra VIC/NVENC devfreq governors to performance
After=nvargus-daemon.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/sh -c 'for d in /sys/class/devfreq/*vic* /sys/class/devfreq/*nvenc*; do echo performance > "$d/governor"; done'

[Install]
WantedBy=multi-user.target

Then enable it:

sudo systemctl daemon-reload
sudo systemctl enable --now tegra-mm-perf.service

The *vic* and *nvenc* patterns make the service work on Jetson modules with different device addresses.