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013c2519dc
The full chain — mDNS discovery, signaling negotiation, RTP over Wi-Fi, software H.264 decode, and fullscreen KMSDRM letterboxed rendering — is confirmed working on a real two-machine setup (desktop -> Raspberry Pi Zero 2 W headless receiver). The probe gradient appeared on the Pi's display.
99 lines
3.6 KiB
Markdown
99 lines
3.6 KiB
Markdown
# Development Phases
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This file breaks the project into incremental milestones. Each phase produces a
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working, testable slice of functionality. Do not start a phase until the
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previous one is validated.
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## Phase 1 — Project Skeleton
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**Goal**: configure, compile, and run tests with no real dependencies.
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- [x] Meson build files (`meson.build`, `meson_options.txt`).
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- [x] Public module headers with `namespace sc`.
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- [x] Unit test that exercises a trivial utility function.
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- [x] `README.md` with build instructions.
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**Validation**: `meson setup build && meson compile -C build && meson test -C build`.
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## Phase 2 — Software H.264 Encode / Decode
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**Goal**: encode raw pixel buffers to H.264 and decode them back, purely with
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FFmpeg software paths.
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- [x] Add `libavcodec`, `libavutil`, `libswscale` dependencies.
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- [x] Implement `EncoderFactory::create()` and `Encoder::encode()`.
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- [x] Implement `DecoderFactory::create()` and `Decoder::decode()`.
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- [x] Round-trip test: synthetic RGB frames → H.264 → decoded RGB.
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**Validation**: unit test produces visually/structurally correct round-trip
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frames.
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## Phase 3 — PipeWire Screen Capture
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**Goal**: capture the desktop and feed frames into the encoder.
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- [x] Add `libpipewire-0.3` dependency.
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- [x] Implement `CaptureFactory::create()` using the xdg-desktop-portal.
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- [x] Wire `CaptureSession::next_frame()` → `Encoder::encode()` in a local smoke
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test that just writes a few encoded frames to disk.
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**Validation**: manual run on a real Linux desktop session produces a valid
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H.264 bitstream.
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## Phase 4 — RTP Framing
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**Goal**: packetize NAL units into RTP and depacketize them.
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- [x] Implement `RtpHeader` and `RtpPacket` serialize/parse.
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- [x] Add H.264 NAL splitting and FU-A fragmentation.
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- [x] Unit test for serialization, fragmentation, and reassembly.
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**Validation**: unit tests cover single-NAL and fragmented packet paths.
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## Phase 5 — Local UDP Sender → Receiver Loopback
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**Goal**: send RTP packets over UDP and render the result locally.
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- [x] Implement `RtpTransport` with ASIO or raw UDP sockets.
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- [x] Wire sender pipeline: capture → encode → RTP → localhost UDP.
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- [x] Wire receiver pipeline: localhost UDP → RTP → decode → renderer.
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- [x] Add SDL2/SDL3 dependency and a minimal `Renderer`.
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**Validation**: `screencast --send` and `screencast --receive` on the same
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machine show the captured desktop in a window.
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## Phase 6 — LAN Signaling and Discovery
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**Goal**: two peers on the same LAN can find each other and negotiate a
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session.
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- [x] Implement mDNS/DNS-SD discovery with Avahi.
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- [x] Implement JSON signaling (newline-delimited JSON over TCP for now;
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the WebSocket transport is deferred to Phase 7 with its dependency).
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- [x] Extend CLI with `--peer` and `--discover`.
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**Validation**: two peers connect without hard-coded IP addresses.
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Validated over loopback AND on real two-machine hardware: a Raspberry
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Pi Zero 2 W (Wi-Fi, headless KMSDRM, systemd autostart) was discovered,
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negotiated with, and streamed to from the desktop; the receiver rendered
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a synthetic feed fullscreen on its display. On that network the LAN's
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6to4 addresses are unreachable between peers, so senders try all
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discovered addresses in reachability order (private IPv4 first).
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## Phase 7 — Resilience and Polish
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**Goal**: loss recovery, hardware acceleration, and packaging.
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- NACK / PLI feedback loop.
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- Jitter buffer on the receiver.
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- VAAPI/NVENC hardware encode probes and fallback.
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- Optional GUI target behind `meson -Dgui=true`.
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- `.desktop` file, icon, packaging notes.
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**Validation**: sustained streaming under packet loss; hardware accel smoke
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where available.
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## Current phase
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Phase 7 — Resilience and Polish.
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