fegger
3f8e92c6af
The first real sender/receiver run failed permanently: the receiver reported 'non-existing PPS 0' for every frame. Without a VBV, a 2256x1504 IDR keyframe bursts hundreds of kilobytes of back-to-back FU-A packets, overflowing the ~208KB default UDP receive buffer; the resulting sequence gap made the depacketizer drop whole keyframes including their in-band SPS/PPS, so the decoder never initialized and never recovered, because every keyframe burst overflowed again. - Encoder: add rc_max_rate = bitrate and rc_buffer_size = bitrate*2/fps, capping any single frame to about two frame periods of bytes (~40KB at the 4Mbps default). - Encoder: switch the time_base to microseconds. It was derived from the configured frame rate, which quantized capture-rate timestamps and duplicated pts; RTP timestamps are now lossless. - Transport: request a 4MB SO_RCVBUF on the receive socket (best-effort; the kernel clamps to net.core.rmem_max). meson test 4/4, valgrind clean (loopback + codec).
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Runbook — build and validation commands
Reusable validation steps for this repository. Run the relevant ones before considering a change complete.
Build and test
meson setup build # once
meson compile -C build
meson test -C build --print-errorlogs
Memory and correctness checks (codec changes)
Run the codec round-trip test under valgrind after touching the encoder or decoder:
valgrind --leak-check=full --errors-for-leak-kinds=definite \
build/tests/test_codec_roundtrip
Expected: no "definitely lost" bytes and no "Invalid read/write" errors. FFmpeg may keep some "still reachable" allocations at exit; that is normal.
This check caught two real defects in the Phase 2 decoder: a per-packet payload leak and an unpadded extradata buffer over-read. Keep using it.
Capture smoke test (Phase 3, manual)
Requires a running desktop session with xdg-desktop-portal and a backend
that implements the ScreenCast portal (e.g. Hyprland, GNOME, KDE). The
portal shows an interactive source picker, so this cannot run unattended.
meson compile -C build # builds tools/capture_smoke
./build/tools/capture_smoke 10 out.h264 # captures 10 frames
ffprobe -v error -show_entries stream=codec_name,width,height out.h264
Expected: the tool prints the negotiated resolution/format/stride and
writes a non-empty file; ffprobe reports codec_name=h264 and the correct
width/height. The encoder prepends its Annex-B SPS/PPS extradata so the
file is a self-contained elementary stream.
If you see impl_ext_end_proxy called from wrong context warnings, a
PipeWire proxy operation ran without the thread-loop lock — all pw
calls that send messages (connect, stream, core) must happen under
pw_thread_loop_lock.
Sender / receiver loopback (Phase 5, manual)
Two terminals on the same desktop session:
./build/src/app/screencast --receive # terminal 1: window appears
./build/src/app/screencast --send # terminal 2: portal source picker
Expected: the receiver window shows the captured desktop in near real time.
If the receiver starts after the sender, a few non-existing PPS decode
errors are normal until the next keyframe arrives (the GOP is ~0.4s);
video should appear within a second. Stop either side with Ctrl-C.
Optional flags: --port, --peer HOST[:PORT], --bitrate KBPS,
--target window.
Notes: the encoder runs a VBV that caps keyframe bursts to roughly two
frame periods of bytes, and the receiver requests a 4MB UDP receive
buffer (clamped by net.core.rmem_max). For very high --bitrate
values, raise net.core.rmem_max on the receiver machine.
The headless equivalent runs as part of meson test (udp loopback test):
synthetic frames → encode → packetize → localhost UDP → depacketize →
decode, no portal or window involved.
Formatting
find include src tests -type f \( -name '*.cpp' -o -name '*.h' \) \
-exec clang-format --dry-run --Werror {} +