# screencast iOS receiver

A native iOS receiver app (Swift) so an iPhone can act as a second receiver.
It speaks the **existing signaling + RTP protocol unchanged** — no C++ changes —
mirroring the Android receiver (Phase 8) source-to-source.

- **Min iOS:** 17 (validated on iPhone 16 / iOS 26.6.1)
- **No third-party dependencies** — only Apple system frameworks (SwiftUI,
  AVFoundation, VideoToolbox, CoreMedia, BSD sockets).

## Pipeline

```
Bonjour advertise (_screencast._tcp) + TCP signaling server (offer → answer)
  UDP RTP → jitter buffer (16 pkt / 60 ms) → depacketize (single-NAL + FU-A)
  → VideoToolbox H.264 (in-band SPS/PPS) → AVSampleBufferDisplayLayer (letterbox)
```

Recovery matches the C++ receiver: a damaged frame is dropped and a PLI
(rate-limited to one per 500 ms) asks the sender for a keyframe.

## Layout

```
Receiver/
  App/        SwiftUI app, video surface (AVSampleBufferDisplayLayer), controller
  Rtp/        RtpHeader, RtpPacket, JitterBuffer, H264Depacketizer, Avcc, NAL extraction
  Signaling/  SignalingMessage (JSON), LineAssembler, SignalingServer (BSD sockets)
  Decode/     RenderSink, H.264 format description, VideoToolbox decoder
  Support/    UdpTransport (poll-based), LocalAddress
  Pipeline/   ReceiverPipeline (coordinates everything)
ReceiverTests/
  XCTest port of the Android JVM tests + added coverage (signaling, line
  framing, AVCC, NAL extraction)
```

## Build and test (on a Mac with Xcode 26)

```sh
./bootstrap.sh            # installs XcodeGen, generates the project, builds for device
./bootstrap.sh test       # runs the unit tests on the simulator
```

`bootstrap.sh` downloads XcodeGen from the GitHub release into `tools/` (no
Homebrew). Override the simulator with `IOS_DEST="platform=iOS Simulator,name=…"`.

## Install on a device

Free provisioning (or your team) is set in Xcode — this can't be scripted:

1. Open `Receiver.xcodeproj`.
2. Select the **Receiver** target → *Signing & Capabilities* → set your Apple ID
   (a 7-day development certificate is fine for sideloading).
3. Run to the iPhone (USB, trust the computer).

The first run prompts for **Local Network** access — allow it, or the sender
will never discover the phone (silent failure, like the Android
`PROTOCOL_DNS_SD` bug).

## Stream to the phone

On the sender (Linux desktop):

```sh
screencast --send --peer <phone-ip>:5005      # target the phone directly
screencast --discover                          # or list receivers; the phone shows up
```

Expected: the phone shows the captured desktop, letterboxed to its screen, with
PLI recovery on Wi-Fi loss.

## Testing notes

The pure protocol core (RTP, jitter, depacketizer, signaling JSON, line framing,
AVCC, NAL extraction) is unit-tested in the simulator. The VideoToolbox decode
path and the local-network/Bonjour flow are on-device validation items — the
highest-risk parts to verify on the borrowed Mac + iPhone.