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VNOX-Client/docs/05-features/video-screen-audit.md

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Video, Camera & Screen Share — Design Audit

Audits docs/05-features/video.md against the current codebase and roadmap. Each gap has: problem, recommendation, priority, target file.

Summary

video.md provides a solid high-level sketch (video-node, H.264 UDP relay, nokhwa capture, grid UI). But critical details are missing for actual implementation. This audit fills those gaps.

1. Video-node — Integration with existing architecture

Gap 1.1 — Video-node lifecycle

Problem: video.md says "separate binary or embedded in voice-node" but doesn't decide. Voice-node has just been refactored with jitter buffer — video needs the same relay pattern.

Recommendation: Separate binary (vnox-video-node). Video frames are fundamentally different from voice packets (keyframes, fragmentation, higher bandwidth). Keeping them separate avoids coupling and allows independent scaling.

Priority: P0 — must decide before writing a line of code.

Target: video.md — add "Deployment" section.

Gap 1.2 — Channel membership signalling

Problem: Video-node needs to know which users are in which channel. Currently this is managed by gateway. How does video-node learn membership?

Recommendation: Gateway sends VIDEO_SESSION_JOIN / VIDEO_SESSION_LEAVE events to video-node over TCP (internal control channel), same pattern as planned for gateway→voice-node membership signalling (Phase 2 in roadmap).

// Gateway → Video-node (internal TCP)
{
  "event": "VIDEO_SESSION_JOIN",
  "channel_id": 12345,
  "user_id": "<pubkey>",
  "socket_addr": "192.168.1.5:7701"
}

Priority: P0 — video relay can't work without knowing recipients.

Target: video.md — add "Gateway integration" section.

Gap 1.3 — No encryption spec

Problem: Voice packets are encrypted with ChaCha20-Poly1305. Video packets are not addressed — are they encrypted? With what keys?

Recommendation: Same ChaCha20-Poly1305 AEAD as voice. Each video session gets ephemeral keys derived via the same X25519 ECDH + HKDF-SHA256 path used for voice. Video-node does NOT decrypt (transparent relay, same as voice-node).

The session key exchange happens during HELLO handshake — add a video_key field alongside the existing voice_key.

Priority: P0 — security regression if video is plaintext.

Target: video.md — add "Encryption" section; docs/02-protocol/security.md — add video encryption note.

2. Camera Capture — Missing details

Gap 2.1 — nokhwa API surface and fallback

Problem: video.md mentions nokhwa but not the concrete API or what happens on platforms where it doesn't work (Linux v4l2 permissions, Wayland).

Recommendation: Abstract behind a VideoSource trait:

// client/src/video/capture.rs
pub trait VideoSource {
    fn devices() -> Vec<DeviceInfo>;
    fn start(config: StreamConfig) -> Result<FrameStream>;
}

struct NokhwaSource { ... }
struct StubSource { ... }  // fallback

pub struct StreamConfig {
    pub device_id: String,
    pub resolution: Resolution,   // 640x480, 1280x720, 1920x1080
    pub fps: u32,                 // 15, 30
    pub format: PixelFormat,      // NV12, I420, BGRA
}

Make nokhwa a feature gate (same pattern as rnnoise for voice).

Priority: P0 — blocks camera implementation.

Target: New file: client/src/video/capture.rs (spec in video.md).

Gap 2.2 — Device hotplug / switch

Problem: No mention of what happens when camera is unplugged/replugged or user switches camera mid-call.

Recommendation: VideoSource emits events:

enum CaptureEvent {
    Frame(VideoFrame),
    DeviceLost(String),
    DeviceReconnected(String),
    Error(String),
}

Client handles DeviceLost by showing placeholder tile. User can select new device in settings without leaving call.

Priority: P1 — quality of life, not MVP blocker.

Target: video.md — add "Device lifecycle" to capture section.

Gap 2.3 — Resolution / FPS negotiation

Problem: video.md says "720p default, 30 fps" but doesn't say how clients agree on parameters. Different clients have different cameras.

Recommendation: Server advertises max resolution per channel. Client sends its capability in VIDEO_SESSION_JOIN. Server picks min(max_server, max_client) per sender.

# server config
[video.channel_defaults]
max_resolution = "1280x720"
max_fps = 30
max_bitrate_kbps = 2500

Priority: P1 — needed before multi-user video testing.

Target: video.md — add "Capability negotiation" section.

3. Screen Share — Almost entirely missing

Gap 3.1 — Screen capture crate

Problem: video.md mentions "Screen sharing (desktop capture)" as one bullet in Phase 2, no detail.

Recommendation:

Platform Crate Notes
Windows windows-capture or DXGI via winapi DXGI Desktop Duplication API — best perf
Linux X11 x11cap or raw XSHM X11 only, no Wayland
Linux Wayland pipewire via pw-video or xdg-desktop-portal Portal is the standard path
macOS screencapturekit via objc bindings or CGDisplay ScreenCaptureKit requires macOS 13+

Abstract behind same VideoSource trait as camera. Two implementations: CameraSource, ScreenSource.

Priority: P1 — needed for Phase 2 screen share.

Target: New doc: docs/05-features/screen-share.md or extend video.md Phase 2.

Gap 3.2 — Window/display selection UI

Problem: User needs to pick which screen or window to share. No UI spec.

Recommendation: Modal dialog when user clicks "Screen Share":

┌─────────────────────────────────────────┐
│ Share Your Screen                        │
│─────────────────────────────────────────│
│ [Screens]  [Windows]                     │  ← tabs
│─────────────────────────────────────────│
│ ┌──────────┐ ┌──────────┐               │
│ │ Display 1│ │ Display 2│               │
│ │1920×1080 │ │2560×1440 │               │
│ │   [✓]    │ │          │               │
│ └──────────┘ └──────────┘               │
│─────────────────────────────────────────│
│ ☐ Share system audio                    │
│ ☐ Optimize for video (60fps)            │
│─────────────────────────────────────────│
│               [Cancel]  [Share]          │
└─────────────────────────────────────────┘

Priority: P1 — UX blocker for screen share.

Target: video.md — add "Screen share UI" section.

Gap 3.3 — System audio capture with screen

Problem: "Share system audio" checkbox in the mockup — how? No mention in video.md.

Recommendation:

  • Windows: WASAPI loopback (cpal supports it with loopback config)
  • Linux: PulseAudio monitor or PipeWire
  • macOS: BlackHole or ScreenCaptureKit (built-in on 13+)

Feature-gate it: --features screen-audio. Not all platforms support it cleanly.

Priority: P2 — nice to have, not MVP.

Target: video.md Phase 2 — add "System audio" bullet.

Gap 3.4 — Screen share FPS strategy

Problem: Screen share has different FPS needs than camera. Coding: 15fps is fine. Gaming: 60fps needed.

Recommendation: Client detects content type (static → low FPS, motion → high FPS) and adapts. User can override with "Optimize for video" checkbox.

Default: 15fps for screen share, 30fps for camera.

Priority: P2 — optimization, not MVP.

Target: video.md — add to Phase 2.

4. Interaction Model — Video + Voice

Gap 4.1 — Video tied to voice channel

Problem: video.md implies video is in the same channel as voice. What if users want video-only (no voice) or voice-only (no video)?

Recommendation: Video is a capability toggle within a voice channel, not a separate channel type:

  1. User joins voice channel (as today)
  2. User clicks "Enable Camera" → client starts sending video frames to video-node
  3. User clicks "Disable Camera" → stops sending, voice continues
  4. Same for "Share Screen"

Channel membership = voice channel membership. Video is additive.

New voice state: VOICE_STATE gets a video: bool field.

Priority: P0 — architectural decision, affects protocol design.

Target: video.md — add "Interaction model" section; docs/02-protocol/packets.md — extend VOICE_STATE.

Gap 4.2 — Video without voice

Problem: Some users may want to watch a stream without transmitting audio. Current model requires voice channel join.

Recommendation: Phase 1: allow joining voice channel muted+deafened to watch video. Phase 3: separate "watch-only" mode (VIEW permission).

Priority: P2 — Phase 1 workaround is acceptable.

Target: video.md — add "Watch-only mode" to Phase 3.

5. Performance & Quality

Gap 5.1 — Bitrate adaptation

Problem: No mechanism to adjust video bitrate based on network conditions. Voice has jitter buffer adaptation, video has nothing.

Recommendation: Client-side adaptive bitrate (ABR):

  • Measure packet loss and RTT from video-node ACKs
  • Adjust encoder bitrate up/down based on available bandwidth
  • 3 tiers: low (500kbps), medium (1500kbps), high (4000kbps)

Video-node sends periodic VIDEO_STATS with per-receiver loss rates:

{
  "channel_id": 12345,
  "receivers": {
    "user_a": { "loss_pct": 0.5, "rtt_ms": 12 },
    "user_b": { "loss_pct": 8.0, "rtt_ms": 150 }
  }
}

Priority: P1 — needed for real-world use.

Target: video.md — add "Adaptive bitrate" section.

Gap 5.2 — Simulcast design

Problem: "Simulcast" is listed as Phase 3 with no design. Different receivers have different bandwidth.

Recommendation: Sender encodes 2-3 quality layers. Video-node forwards appropriate layer to each receiver based on their reported bandwidth.

Sender → encode:  1080p (4Mbps) + 720p (1.5Mbps) + 360p (500kbps)
                         │
                   Video-node
                    ╱    │    ╲
            1080p→A  720p→B  360p→C  (based on per-receiver stats)

Requires VP9 SVC or H.264 simulcast. Complex — Phase 3 is correct.

Priority: P2 — Phase 3, but design it now to avoid architecture lock-in.

Target: video.md Phase 3 — expand "Simulcast" bullet.

Gap 5.3 — Keyframe interval

Problem: New viewers joining mid-stream need a keyframe to start decoding. Video.md doesn't mention keyframe strategy.

Recommendation:

  • Sender inserts keyframe every 2 seconds (configurable)
  • Video-node caches last keyframe per sender
  • On new viewer join: video-node sends cached keyframe immediately, then regular frames
  • VIDEO_SESSION_JOIN triggers keyframe push

Add REQUEST_KEYFRAME packet for explicit PLI (Picture Loss Indication).

Priority: P1 — new viewers can't see video without keyframe.

Target: video.md — add "Keyframe handling" section.

6. Missing Protocol Details

Gap 6.1 — No packet fragmentation spec

Problem: Video frames can be 50-100KB. UDP MTU is ~1400 bytes. Video.md says "Packetize into MTU-friendly chunks" but doesn't define the fragmentation protocol.

Recommendation: Reuse the LNEx fragmentation flags from the base packet header (bits 2-3):

FRAGMENTED (bit 2) + LAST_FRAG (bit 3)

Each video frame:

  1. Split into 1400-byte chunks
  2. Each chunk gets same frame_seq, incrementing fragment_seq
  3. Last chunk sets LAST_FRAG flag
  4. Receiver reassembles before decode

New packet type: VIDEO_FRAME_FRAGMENT (0x0012) — separate from unfragmented VIDEO_FRAME (0x0011).

Wait — VIDEO_FRAME ID isn't assigned in the packet registry yet. Register:

0x0011  VIDEO_FRAME        single (small) video frame, no fragmentation
0x0012  VIDEO_FRAME_FRAG   fragment of a larger video frame

Priority: P0 — video can't work over UDP without fragmentation.

Target: video.md — replace packet format section; docs/02-protocol/packets.md — add 0x0011/0x0012 to registry.

Gap 6.2 — No RTCP-like receiver reports

Problem: Sender has no feedback about what receivers are experiencing. Voice has implicit feedback (jitter buffer stats), video needs explicit.

Recommendation: Minimal receiver report packet:

// 0x0013 VIDEO_RECEIVER_REPORT — client → video-node → sender
{
  "frame_seq": 1042,
  "loss_cumulative": 15,
  "loss_fraction": 2,       // percent of last N packets
  "jitter_ms": 8,
  "rtt_ms": 35
}

Client sends every 1 second. Video-node aggregates and forwards to sender.

Priority: P1 — needed for ABR and quality adaptation.

Target: video.md — add "Receiver reports" section.

7. Guild Integration (Phase 1.2)

Gap 7.1 — Video permissions already defined

Status: ✅ STREAM (bit 18) permission is already in the community model (docs/07-community-model.md). Covers both camera and screen share.

No gap here — just implement the check in gateway when processing VIDEO_SESSION_JOIN.

Gap 7.2 — Channel-level video settings

Problem: Guild admins may want to disable video in certain channels (text-only channels, AFK channel).

Recommendation: Add video_allowed: bool to channel config. Default: true for voice channels, false for text channels.

ALTER TABLE channels ADD COLUMN video_allowed BOOLEAN NOT NULL DEFAULT 1;

Gateway rejects VIDEO_SESSION_JOIN if video_allowed = false.

Priority: P1 — admin control expected by guild owners.

Target: docs/10-database.md — add column to channels table; docs/07-community-model.md — add video_allowed to channel settings.

8. Mobile Considerations (Phase 3)

Gap 8.1 — Front/back camera switch

Problem: Mobile video.md doesn't mention camera switching at all.

Recommendation: Mobile client sends CAMERA_SWITCH event to video-node — no protocol change needed, just local capture change. New frame stream with camera: front|back metadata.

Priority: P2 — Phase 3.

Target: docs/04-clients/mobile.md (doesn't exist yet — create in Phase 3).

Gap 8.2 — Self preview

Problem: Desktop video grid has "Self-view (small, picture-in-picture corner)". On mobile the self-view is more important (front camera framing).

Recommendation: Mobile layout: self-view full-width at top, other participants in scrollable grid below. Toggle button to swap.

Priority: P2 — Phase 3.

Target: docs/04-clients/mobile.md.

Gap Summary — What to Add Before Implementation

# Gap Priority Target file
1 Video-node binary decision + deployment P0 video.md
2 Gateway membership signalling to video-node P0 video.md
3 Video encryption (ChaCha20-Poly1305) P0 video.md, security.md
4 Video frame fragmentation protocol P0 video.md, packets.md
5 Video ↔ voice interaction model P0 video.md, packets.md
6 VideoSource trait + feature-gated nokhwa P0 video.md
7 Keyframe caching + PLI request P1 video.md
8 Receiver reports (RTCP-like) P1 video.md
9 Adaptive bitrate design P1 video.md
10 Screen share crate selection + ScreenSource P1 video.md
11 Window/display selection UI P1 video.md
12 Resolution/FPS negotiation P1 video.md
13 Channel-level video_allowed setting P1 database.md, community-model.md
14 Camera hotplug/switch handling P1 video.md
15 Video-only (watch) mode P2 video.md
16 System audio with screen share P2 video.md
17 Screen share FPS strategy P2 video.md
18 Simulcast design P2 video.md
19 Mobile front/back camera + self preview P2 mobile.md

Recommended Implementation Order

  1. Update video.md — incorporate P0 and P1 gaps from this audit into the design doc
  2. Register packet types — 0x0011–0x0013 in packets.md
  3. Video-node prototype — separate binary, UDP relay, no encoding/decoding (transparent relay like voice)
  4. Gateway ↔ video-node signalling — internal TCP control channel for membership
  5. Client camera capture — VideoSource trait + NokhwaSource behind feature gate
  6. Fragmentation — implement FRAGMENTED/LAST_FRAG for video frames
  7. Grid UI — basic 2×2 grid in client
  8. Encryption — ChaCha20-Poly1305 for video frames
  9. ABR + receiver reports — iterate toward production quality
  10. Screen share — ScreenSource implementation + picker UI