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36d086af4e
Four encoder quality improvements, all sender-side: - CRF rate control (default 22, --crf to override): targets a constant visual quality level instead of a fixed bitrate. Static desktop content uses 300-800 kbps (vs. forced 4000+), and the saved bits go to sharp text and clean motion when they appear. The VBV max rate (the --bitrate value, now a cap rather than a target) bounds bursts so the receiver's UDP buffers stay safe. Round-trip test bitrate dropped from 1390 kb/s to 47 kb/s on synthetic frames — the encoder uses only what it needs. - 5-second GOP (was 1 second): 80% fewer keyframe bits freed for detail frames. Screen content changes incrementally, not wholesale; PLI feedback recovers from loss in one frame time regardless of GOP length. - faster preset (was veryfast): better sub-pixel estimation and RDO on more decisions. The desktop handles it trivially at 1080p. - Screen-content x264 tuning: aq-mode=2 (auto-variance AQ moves bits away from flat areas toward text edges) and psy-rd=1.5 (preserves texture sharpness). Combined with the earlier veryfast upgrade and sender-side downscaling, this is roughly 2x the perceived quality at the same average bandwidth compared to the original ultrafast ABR encoder. meson test 5/5 in both configurations, valgrind clean.
screen_cast
A native Linux peer-to-peer screencast application.
- Send your desktop or a window to another Linux machine.
- Receive a stream and render it in a window.
- Discover receivers on the LAN via mDNS/Avahi; negotiate sessions with JSON signaling; stream H.264 over RTP/UDP.
Built with C++20, Meson, PipeWire, FFmpeg, and SDL3.
Quick start
Requirements:
- C++20 compiler with
<format>(GCC 13+, Clang 18+) - Meson >= 0.63, Ninja
- FFmpeg development packages (
libavcodec,libavutil,libswscale) - SDL3 development package (
sdl3) - nlohmann JSON (
nlohmann_json) and Avahi client (avahi-client) - For the sender only: PipeWire dev (
libpipewire-0.3) and libportal
Build and run tests:
meson setup build
meson compile -C build
meson test -C build --print-errorlogs
Stream between two machines:
screencast --receive # machine A: announces itself, opens a window
screencast --send # machine B: discovers A, negotiates, streams
See docs/RUNBOOK.md for all modes, flags, and validation procedures.
Receiver on a small ARM board (e.g. Raspberry Pi Zero 2 W)
The receiver does not need the sender's PipeWire/portal capture stack. On the board, run:
sudo ./scripts/install-receiver.sh
screencast --receive
The script installs the dependencies, builds a receiver-only binary
(-Dsender=false), runs the test suite, and installs to /usr/local/bin
(override with SC_RECEIVER_INSTALL_DIR). It needs Raspberry Pi OS Trixie
or newer (GCC 13+ for C++20 <format>), builds SDL3 from source when the
distribution does not package it, and enables avahi-daemon. It also
installs and enables a systemd service so the receiver starts at boot —
systemctl status screencast-receiver to check on it.
Performance note: decoding is software H.264; on very small boards expect smooth playback for modest resolutions and reduced frame rates at high resolutions. Hardware decode is planned for Phase 7. On a headless console the receiver runs fullscreen automatically with aspect-preserving letterboxing.
Architecture
See docs/ARCHITECTURE.md for module boundaries and design rules.
Roadmap
Development is split into phases in docs/PHASES.md.
Current phase: Phase 7 — Resilience and polish.
License
MIT — see LICENSE (to be added).