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# Development Phases
This file breaks the project into incremental milestones. Each phase produces a
working, testable slice of functionality. Do not start a phase until the
previous one is validated.
## Phase 1 — Project Skeleton
**Goal**: configure, compile, and run tests with no real dependencies.
- [x] Meson build files (`meson.build`, `meson_options.txt`).
- [x] Public module headers with `namespace sc`.
- [ ] Unit test that exercises a trivial utility function.
- [ ] `README.md` with build instructions.
**Validation**: `meson setup build && meson compile -C build && meson test -C build`.
## Phase 2 — Software H.264 Encode / Decode
**Goal**: encode raw pixel buffers to H.264 and decode them back, purely with
FFmpeg software paths.
- Add `libavcodec`, `libavutil`, `libswscale` dependencies.
- Implement `EncoderFactory::create()` and `Encoder::encode()`.
- Implement `DecoderFactory::create()` and `Decoder::decode()`.
- Round-trip test: synthetic RGB frames → H.264 → decoded RGB.
**Validation**: unit test produces visually/structurally correct round-trip
frames.
## Phase 3 — PipeWire Screen Capture
**Goal**: capture the desktop and feed frames into the encoder.
- Add `libpipewire-0.3` dependency.
- Implement `CaptureFactory::create()` using the xdg-desktop-portal.
- Wire `CaptureSession::next_frame()``Encoder::encode()` in a local smoke
test that just writes a few encoded frames to disk.
**Validation**: manual run on a real Linux desktop session produces a valid
H.264 bitstream.
## Phase 4 — RTP Framing
**Goal**: packetize NAL units into RTP and depacketize them.
- Implement `RtpHeader` and `RtpPacket` serialize/parse.
- Add H.264 NAL splitting and FU-A fragmentation.
- Unit test for serialization, fragmentation, and reassembly.
**Validation**: unit tests cover single-NAL and fragmented packet paths.
## Phase 5 — Local UDP Sender → Receiver Loopback
**Goal**: send RTP packets over UDP and render the result locally.
- Implement `RtpTransport` with ASIO or raw UDP sockets.
- Wire sender pipeline: capture → encode → RTP → localhost UDP.
- Wire receiver pipeline: localhost UDP → RTP → decode → renderer.
- Add SDL2/3 dependency and a minimal `Renderer`.
**Validation**: `screencast --send` and `screencast --receive` on the same
machine show the captured desktop in a window.
## Phase 6 — LAN Signaling and Discovery
**Goal**: two peers on the same LAN can find each other and negotiate a
session.
- Implement mDNS/DNS-SD discovery with Avahi.
- Implement JSON WebSocket signaling.
- Extend CLI with `--peer-address` or `--discover`.
**Validation**: two machines on the same LAN connect without hard-coded IP
addresses.
## Phase 7 — Resilience and Polish
**Goal**: loss recovery, hardware acceleration, and packaging.
- NACK / PLI feedback loop.
- Jitter buffer on the receiver.
- VAAPI/NVENC hardware encode probes and fallback.
- Optional GUI target behind `meson -Dgui=true`.
- `.desktop` file, icon, packaging notes.
**Validation**: sustained streaming under packet loss; hardware accel smoke
where available.
## Current phase
Phase 1 — skeleton and tooling.