Fernsicht documentation

Fernsicht is a self-hosted remote desktop and game streaming tool for Linux, written in Rust. It aims for the latency of Sunshine/Moonlight or Parsec with the comfort of TeamViewer: the app finds the other computer in the network, you pair once with a PIN, and a click starts the session. Also as a website with search: https://firsttris.github.io/fernsicht/

Status	what is built, phase by phase, and what has been seen working live
Installation	the AppImage, sharing a computer, the host as a service, building from source, uninstalling
Remote access	over the internet today: Tailscale, Cloudflare WARP, port forwarding
The app	devices, pairing, sessions, the video window and its keys, gaming mode, monitors, settings
Web viewer	any browser in the LAN, phones and tablets with gestures and the on-screen keyboard
Command line	every option of fernsicht-host-agent and fernsicht-client
KMS capture	how the host reads the screen, running it by hand, troubleshooting, limits
Architecture	the pipeline from screen to screen, threads, latency measurement
Modules	every crate, app and web package, and how they fit together
Video path	capture, conversion, encoders, codecs and their negotiation, decoders, the renderer
Protocol	the UDP packets, FEC, pacing, clock sync, reliable input, sound
Security	pairing with SPAKE2, Noise IK sessions, sealed packets, the web viewer's access
Performance	measurements, what is already state of the art, what can still get faster
Next steps	the logical next things to build, with their value and effort
Code review	the review of the whole code base: bugs, security, performance, clean-up, each with its status
Latency baseline	how the comparison with Sunshine/Moonlight is measured
Development	dev container, building with features, checks, releases
Testing	the test layers, from unit tests to fuzzing and real GPUs
GPU runners	setting up a machine as a self-hosted runner for the GPU tests
Handover notes	where the work stands and how to pick it up

How Fernsicht works, in one minute

• Two programs. fernsicht-host-agent runs on the computer you control, usually as the system service fernsicht-host-agent. fernsicht-client shows its screen in a Vulkan window. The app (Tauri) is the friendly face of the client: devices, pairing, settings, sessions.
• The picture stays on the GPU. The host reads the framebuffer the monitor shows (KMS) at each vblank and hands it to the hardware encoder as a DMA-BUF: VAAPI on AMD and Intel, NVENC on NVIDIA via Vulkan and CUDA. The client decodes in hardware and draws the decoded picture straight into its window.
• Its own protocol over UDP. Frames are split into packets with Reed-Solomon FEC sized from the measured loss and paced so switches and Wi-Fi do not overflow. Input is retransmitted until acknowledged, sound is Opus with 5 ms frames. A browser gets the same stream over WebRTC.
• Encrypted, paired devices only. Devices pair once with a 6-digit PIN (SPAKE2). Every session starts with a Noise IK handshake; then every packet is sealed with ChaCha20-Poly1305.
• Measured all the way. Every packet carries the host's timestamps; the client syncs clocks and shows the latency of each stage – capture, encode, network, decode, display – in the overlay.