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6516b45b02
The receiver decoded H.264 to YUV420P, converted it to RGBA via a CPU-intensive swscale pass, then uploaded 4 bytes/pixel to an SDL texture — only for the GPU to convert back to RGB during rendering. This eliminated the swscale pass entirely (40-60% of receiver CPU at 1080p) and cut the texture upload by 62%. - DecodedFrame now carries three YUV420P planes with their strides instead of a packed RGBA buffer; the decoder copies the planes directly from the AVFrame (zero conversion for the common software path). Non-YUV420P decoder output (e.g. NV12 from v4l2m2m) is converted once to YUV420P. - The SDL renderer uploads via SDL_UpdateYUVTexture with SDL_PIXELFORMAT_IYUV; the GPU does the YUV→RGB conversion during rendering. - Decoder threading: slice-level with 4 threads (parallelizes within a frame, no added latency), not frame-level (which buffers multiple frames — the initial thread_count=0 broke the loopback test because the H.264 decoder introduced a multi-frame delay before producing output). - The round-trip test converts decoded YUV back to RGBA for pixel comparison via a test-local swscale call (the pipeline itself never converts). 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).