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SCMF — Simulator Camera Message Format

⚠️ Historical (v0.2.x). SCMF was the wire format between the TCP server and the SimulatorCameraClient iOS SDK, both removed in v1.0.0. Frames now travel through macOS CoreMediaIO via CMIOExtensionStream, so there is no wire protocol and no SDK to link. Kept for reference.

v1 · little-endian on the wire · framed over TCP.

Wire layout

+--------+---------------+------------------+--------+---------+------------------+
| magic  | payloadLength | timestamp        | width  | height  | jpegData         |
| 4 B    | 4 B uint32 LE | 8 B Float64 LE   | 4 B LE | 4 B LE  | payloadLength-16 |
+--------+---------------+------------------+--------+---------+------------------+
Field Type Notes
magic 4 bytes, ASCII 0x53 0x43 0x4D 0x46 — "SCMF"
payloadLength uint32 LE Size of timestamp + width + height + jpegData = 16 + jpegData.count
timestamp Float64 LE Seconds since a server-chosen epoch (monotonic)
width uint32 LE Frame width in pixels
height uint32 LE Frame height in pixels
jpegData bytes Baseline or progressive JPEG, any color space

Integers MUST be little-endian. Decoders should use unaligned loads — the ARM64 Simulator is strict about alignment.

Framing rules

  1. A single TCP connection is a stream of consecutive SCMF frames.
  2. The server MAY send any number of frames. The client MUST drain all complete frames on every read.
  3. If the client reads a frame whose magic is not "SCMF", it MUST close the connection — the stream is corrupt.
  4. If a TCP read yields fewer than 8 + payloadLength bytes, the client MUST buffer and wait for more data.

Transport

  • Default endpoint: 127.0.0.1:9876
  • Localhost-only by default. Servers that expose a LAN port MUST log a warning.
  • No TLS in v1. All frames transit loopback; add TLS in v2 for remote use.

Versioning

The protocol is versioned by the 4th byte of magic. Current SCMF = v1. Future SCMG/SCMH reserved for HEVC / multi-track.

Reference encoder (Swift)

The reference implementation lived in Sources/SimulatorCameraClient/SCMFDecoder.swift (SCMFCodec.encode(_:)), deleted in v1.0.0. To read it, check out the last commit before removal:

git show 3bbc6f6^:Sources/SimulatorCameraClient/SCMFDecoder.swift