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docs/05-features/video.md

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+# Video Chat — Architecture
+
+## Goal
+
+Add real-time video to voice channels.
+Users can share their webcam feed alongside voice.
+
+## Architecture
+
+```
+Current (voice only):
+├─ Gateway: TCP (signaling, chat)
+├─ Voice-node: UDP (Opus voice relay)
+└─ Client: mic → Opus → UDP → voice-node → UDP → client → playback
+
+With video:
+├─ Gateway: TCP (signaling) — UNCHANGED
+├─ Voice-node: UDP (Opus voice) — UNCHANGED
+├─ Video-node: UDP (H.264/VP9 relay) — NEW
+│   └─ Receives encoded frames, relays to channel members
+└─ Client: mic → Opus → UDP → voice-node
+           webcam → H.264 → UDP → video-node ← UDP → decode → display grid
+```
+
+## Video-node
+
+New optional component, separate binary or embedded in voice-node.
+
+### Responsibilities
+- Receive encoded video frames over UDP
+- Relay to all other clients in the same voice channel
+- No transcoding (relay only — CPU efficient)
+- Max resolution / bitrate per channel configurable
+
+### Packet format
+
+```json
+{
+    "packet_id": "VIDEO_FRAME",
+    "channel_id": 12345,
+    "sender_id": "<pubkey>",
+    "frame_seq": 42,
+    "codec": "h264",           // or "vp9"
+    "keyframe": false,
+    "data": "<base64 encoded frame>"
+}
+```
+
+Initially JSON (matching Phase 1 convention), binary framing in Phase 2.
+
+## Client capture pipeline
+
+New file: `client/src/video/capture.rs`
+
+1. Enumerate webcam devices via `nokhwa` or `video4linux`
+2. Capture frames at configurable resolution (720p default)
+3. Encode to H.264 via `ffmpeg-next` or hardware encoder
+4. Packetize into MTU-friendly chunks
+5. Send over UDP to video-node
+
+### Dependencies
+
+- `nokhwa` — cross-platform camera capture (Rust)
+- `ffmpeg-next` or `rav1e` — H.264/VP9 encoding
+
+## Client UI — Video grid
+
+New component: `client/src/ui/video.rs`
+
+- Grid layout (max 4×4 = 16 participants visible)
+- Active speaker highlight (green border)
+- Self-view (small, picture-in-picture corner)
+- Mute video button per participant
+- Resolution/quality indicator per stream
+
+Layout modes:
+- 1 participant → full width
+- 2-4 → 2×2 grid
+- 5-9 → 3×3 grid
+- 10-16 → 4×4 grid with scrolling
+
+## Implementation phases
+
+### Phase 1 (MVP)
+- H.264 encoding with `nokhwa` + `ffmpeg-next`
+- Single video-node binary
+- 2×2 grid in UI
+- 720p max resolution, 30 fps
+
+### Phase 2
+- VP9 support (better quality/bitrate)
+- Adaptive resolution (auto downscale on packet loss)
+- Picture-in-picture self-view
+- Screen sharing (desktop capture)
+
+### Phase 3
+- Hardware encoding (NVENC/VAAPI)
+- Simulcast (different resolution per stream)
+- Recording support