Command line

Both programs work without the app. The app and the host service use the same options.

Host: fernsicht-host-agent

Streams this computer's screen to paired clients. Without a command it runs the host; the commands talk to a running host (for example the system service).

fernsicht-host-agent [OPTIONS]
fernsicht-host-agent pair      # open pairing, show the PIN for the new device
fernsicht-host-agent status    # the host's key, paired devices, the session
fernsicht-host-agent unpair X  # forget a paired device (its key, or a name only it has); its session ends
fernsicht-host-agent disconnect  # end the running session (a device's or a browser's)

Option	Default
--bind <addr>	0.0.0.0:47800	UDP address to listen on
--max-width, --max-height	3840, 2160	upper bound for the stream size; a client asking for the host's size gets the screen's, scaled down to fit
--max-fps	144	upper bound for the frame rate a client may ask for
--max-bitrate	80000	upper bound for the bitrate, kbit/s
--encoder	synthetic	auto (the GPU's: VAAPI on AMD/Intel, NVENC on NVIDIA; with several GPUs the one that drives a monitor), vaapi, nvenc, vulkan (Vulkan Video on the GPU behind --render-node, encoding), or synthetic (no GPU, no real picture). The service uses auto. The hardware encoders need the build features vaapi / nvidia / vulkan
--render-node	/dev/dri/renderD128	GPU render node for VAAPI
--cuda-device	0	CUDA device index for NVENC
--capture	test-pattern	test-pattern or kms (the monitor; build feature kms, needs CAP_SYS_ADMIN, see KMS capture)
--kms-card	first card with a display	e.g. /dev/dri/card1
--kms-connector	first active display	the monitor a session starts with, e.g. DP-1; switching during the session is possible
--audio	desktop with KMS, off with the test pattern	desktop (what this computer plays), tone (440 Hz test tone), off
--input	off	accept mouse, keyboard and gamepads from paired clients (virtual devices through /dev/uinput); with it the desktop's clipboard is shared
--no-clipboard		do not share the desktop's clipboard with clients
--pair		open pairing for 5 minutes at start and show the PIN
--state-dir	/var/lib/fernsicht as root, else ~/.config/fernsicht/host	the host's key and paired clients
--control	/run/fernsicht/control.sock for the service, else the user's runtime directory	the running host's control socket
--web <addr>	0.0.0.0:47800	TCP address of the web viewer (page and API)
--no-web		no web viewer
--web-root	../share/fernsicht/viewer next to the program	the built web viewer (web/viewer/dist)
--no-gpu-boost		leave the GPU's clocks alone during sessions
--pace-mbit	400	highest pacing rate in Mbit/s for what goes beyond a 64 KiB burst (keyframes); the host paces at the rate the client measures the path deliver, up to this
--loss <f>	0	drop this fraction of outgoing video packets (testing, e.g. 0.01)

Client: fernsicht-client

Shows the host's screen in a window (build feature window) and prints the latency overlay once per second.

fernsicht-client [OPTIONS] <HOST>
fernsicht-client discover [ADDRESS…] [--wait <s>]   # look for hosts in the local network (and at these addresses), 1.5 s
fernsicht-client pair <HOST> <PIN> [--name <NAME>]  # pair with a host that shows a PIN; NAME is how it lists this device (default: the hostname)
fernsicht-client hosts               # list the paired hosts
fernsicht-client forget <HOST>       # forget a paired host

<HOST> is the paired host's name or address, e.g. zentrale or 192.168.1.20 (port 47800 unless given).

Option	Default
--width, --height	0	stream size; 0 = the host's screen size
--fps	60	frame rate
--bitrate	0	kbit/s; 0 = chosen by the host for the size (20 Mbit/s for 1080p60, about 36 for 1440p60)
--codec	auto	auto (the best this machine decodes in hardware and the host encodes: AV1, HEVC, else H.264), h264, hevc, av1
--smooth		after a loss the picture goes on and mends itself within half a second instead of waiting for a keyframe (NVIDIA hosts; others ignore it)
--decoder	auto	hardware decoder: auto (Vulkan Video, else VAAPI, else NVDEC), vulkan, vaapi, nvdec (decoding)
--render-node	/dev/dri/renderD128	GPU render node for VAAPI
--gaming		gaming mode: a click captures the pointer, which then moves relatively
--view-only		send no mouse or keyboard input
--no-audio		do not play the host's sound
--no-gamepad		leave this machine's gamepads out
--no-clipboard		do not share this machine's clipboard with the host
--headless		no window: decode only and print the overlay
--record <file>		save the received video: ffplay file.h264; HEVC as file.h265; AV1 is raw OBUs, ffplay -f obu file.obu
--duration <s>	until Ctrl+C	stop after this many seconds
--state-dir	~/.config/fernsicht	this device's key and paired hosts
--loss <f>	0	drop this fraction of incoming video packets (testing)

The window's keys are on the app page.

Examples

# Host by hand, the monitor with real video (as root, see kms-capture.md)
sudo fernsicht-host-agent --capture kms --encoder auto --input --pair

# Client: find, pair, connect
fernsicht-client discover
fernsicht-client pair zentrale 482913
fernsicht-client zentrale --fps 120 --codec hevc

# Without a window, video into a file
fernsicht-client zentrale --headless --duration 10 --record ~/test.h265

# Loss on purpose: what FEC hides
fernsicht-client zentrale --loss 0.01 --duration 10

The overlay in the terminal:

Glass-to-Glass 2,3 ms  (p95 3,0 ms, max 4,0 ms)
Capture 0,7 ms · Encode 0,2 ms · Netz 1,0 ms · Decode 0,3 ms · Anzeige 0,0 ms
Codec Synthetisch · Bildrate 60 fps · Bitrate 24 Mbit/s · Verlust (FEC) 1,0 % → 0 · RTT 0,1 ms

If keyframes drop (RcvbufErrors in /proc/net/snmp), raise the UDP buffers' limit (the host service as root sets its own past it; the client and a host without root need this):

sudo sysctl -w net.core.rmem_max=8388608 net.core.wmem_max=8388608