fegger
236584c240
UDP receive buffers clamp to net.core.rmem_max, whose stock Debian default (~208 KB) is smaller than one VBV-bounded keyframe burst at moderate-to-high bitrates. The resulting packet loss damages every keyframe, drop-on-damage discards them silently, and the receiver shows a black screen with no journal errors while the sender streams happily. The install script now raises rmem_max to 4 MB and persists the sysctl; buffers are allocated lazily, so this costs no RAM at rest. Wi-Fi-only boards (Pi Zero 2 W) remain bandwidth-bound — the RUNBOOK points at --bitrate as the tuning knob.
150 lines
6.0 KiB
Markdown
150 lines
6.0 KiB
Markdown
# Runbook — build and validation commands
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Reusable validation steps for this repository. Run the relevant ones before
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considering a change complete.
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## Build and test
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```sh
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meson setup build # once
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meson compile -C build
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meson test -C build --print-errorlogs
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```
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## Memory and correctness checks (codec changes)
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Run the codec round-trip test under valgrind after touching the encoder or
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decoder:
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```sh
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valgrind --leak-check=full --errors-for-leak-kinds=definite \
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build/tests/test_codec_roundtrip
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```
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Expected: no "definitely lost" bytes and no "Invalid read/write" errors.
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FFmpeg may keep some "still reachable" allocations at exit; that is normal.
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This check caught two real defects in the Phase 2 decoder: a per-packet
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payload leak and an unpadded extradata buffer over-read. Keep using it.
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## Capture smoke test (Phase 3, manual)
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Requires a running desktop session with `xdg-desktop-portal` and a backend
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that implements the ScreenCast portal (e.g. Hyprland, GNOME, KDE). The
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portal shows an interactive source picker, so this cannot run unattended.
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```sh
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meson compile -C build # builds tools/capture_smoke
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./build/tools/capture_smoke 10 out.h264 # captures 10 frames
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ffprobe -v error -show_entries stream=codec_name,width,height out.h264
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```
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Expected: the tool prints the negotiated resolution/format/stride and
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writes a non-empty file; `ffprobe` reports `codec_name=h264` and the correct
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width/height. The encoder prepends its Annex-B SPS/PPS extradata so the
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file is a self-contained elementary stream.
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If you see `impl_ext_end_proxy called from wrong context` warnings, a
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PipeWire proxy operation ran without the thread-loop lock — all pw
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calls that send messages (connect, stream, core) must happen under
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`pw_thread_loop_lock`.
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## LAN discovery and signaling (Phase 6)
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Two machines on the same LAN (mDNS via avahi-daemon, which must be running
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on both):
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```sh
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screencast --receive # machine A: announce + window
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screencast --send # machine B: discovers A, negotiates, streams
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screencast --discover # list receivers on the LAN
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```
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`--send` without `--peer` requires exactly one discovered receiver. Use
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`--peer HOST[:PORT]` to target a receiver directly (signaling port defaults
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to 5005), e.g. `--peer 192.168.178.20`.
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Operational note: never `kill -9` a running receiver — a SIGKILLed process
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cannot withdraw its mDNS registration, and avahi-daemon then keeps broken
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records for that service name until they expire (~75 min), making resolution
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time out for every peer. If that happens, `systemctl restart avahi-daemon`
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clears it. Always stop screencast with Ctrl-C (SIGTERM).
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## Receiver as a systemd service (autostart)
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`scripts/install-receiver.sh` installs and enables
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`screencast-receiver.service` (see `systemd/screencast-receiver.service`).
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It starts at boot after the network and avahi-daemon, and restarts on
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failure. On a headless console SDL renders via KMSDRM; on a desktop
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autologin, edit `/etc/systemd/system/screencast-receiver.service` and
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uncomment the Environment lines for `XDG_RUNTIME_DIR`/`WAYLAND_DISPLAY`.
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```sh
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systemctl status screencast-receiver # is it running?
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journalctl -u screencast-receiver -f # follow logs
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sudo systemctl stop screencast-receiver # graceful; withdraws mDNS
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sudo systemctl disable --now screencast-receiver # turn autostart off
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```
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Verified behavior: `systemctl stop` results in a clean exit (success,
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no restart) and the mDNS announcement is withdrawn — senders stop finding
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the receiver immediately.
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## Headless receiver (no window manager)
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The receiver does not need X11, Wayland, or any window manager: SDL3's
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KMSDRM backend renders straight to the kernel display pipeline. This is
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the recommended setup for small boards (Raspberry Pi OS **Lite**):
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1. No desktop may be enabled — a running compositor holds the DRM master
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and the receiver cannot take it (the two modes are mutually exclusive).
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No console autologin is needed either.
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2. The service renders on its **own VT (tty7)** and switches to it at
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boot: `Ctrl+Alt+F1` returns to the console login, `Ctrl+Alt+F7` back
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to the screencast. (A service must not target tty1: acquiring a tty
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that the console session or getty owns blocks the start forever.)
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3. Disable console blanking: append `consoleblank=0` to
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`/boot/firmware/cmdline.txt` and reboot.
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Under KMSDRM the receiver goes **fullscreen automatically**, with
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aspect-preserving letterboxing (a 4:3 desktop on a 16:9 TV shows black
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bars, not a stretched picture) and no mouse cursor. On desktop sessions
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`--fullscreen` forces the same behavior.
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A window manager only comes with the desktop-session alternative, where
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the receiver runs inside it (uncomment the `Environment=` lines in the
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service file as described above).
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## Sender / receiver loopback (Phase 5, manual)
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Two terminals on the same desktop session:
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```sh
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./build/src/app/screencast --receive # terminal 1: window appears
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./build/src/app/screencast --send # terminal 2: portal source picker
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```
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Expected: the receiver window shows the captured desktop in near real time.
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If the receiver starts after the sender, a few `non-existing PPS` decode
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errors are normal until the next keyframe arrives (the GOP is ~0.4s);
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video should appear within a second. Stop either side with Ctrl-C.
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Optional flags: `--port`, `--peer HOST[:PORT]`, `--bitrate KBPS`,
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`--target window`.
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Notes: the encoder runs a VBV that caps keyframe bursts to roughly two
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frame periods of bytes, and the receiver requests a 4MB UDP receive
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buffer (clamped by `net.core.rmem_max`; the install script raises it to
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4 MB and persists the change). The remaining bottleneck on Wi-Fi-only
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boards is the wireless link itself — lower `--bitrate` until the stream
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is stable.
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The headless equivalent runs as part of `meson test` (`udp loopback` test):
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synthetic frames → encode → packetize → localhost UDP → depacketize →
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decode, no portal or window involved.
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## Formatting
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```sh
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find include src tests -type f \( -name '*.cpp' -o -name '*.h' \) \
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-exec clang-format --dry-run --Werror {} +
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``` |