SIYI HM30 — RTP H.264 Receiver Dashboard

A production-grade, low-latency C++17/Qt5 dashboard that receives and displays raw RTP/UDP H.264 streams from a DJI Osmo Action 5 Pro via the SIYI HM30 datalink.

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Quick Start

# 1. Install dependencies
sudo apt install -y build-essential cmake pkg-config qtbase5-dev \
    libavformat-dev libavcodec-dev libswscale-dev libavutil-dev

# 2. Build
mkdir -p build && cd build && cmake .. -DCMAKE_BUILD_TYPE=Release && make -j$(nproc)

# 3. Run (default URL udp://0.0.0.0:5600)
./build/hm30_rtp_receiver

For a custom stream URL: ./build/hm30_rtp_receiver --url rtsp://192.168.144.25:8554/stream

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Key Features

Feature	Detail
Transport	Passive RTP/UDP listener (no RTSP handshake)
Codec	H.264 via FFmpeg direct — no OpenCV
Threading	Decoder on a dedicated QThread; UI never blocks
Thread safety	std::atomic stats; deep-copied QImage across signal boundary
Styling	100% QSS-driven with dynamic properties — zero runtime setStyleSheet()
Self-contained	QSS embedded in binary via Qt Resource System
Reconnection	Automatic on stream loss with 100 ms back-off
Latency	Sub-frame (no RTSP overhead, fflags=nobuffer, max_delay=0)

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Data Flow

DJI Osmo Action 5 Pro
    └─ H.264 ──► GStreamer (stream_to_siyi.sh)
                    └─ RTP/UDP ──► HM30 Air ──[radio]──► HM30 Ground
                                                              └─ Ethernet ──► This app (udp://0.0.0.0:5600)
                                                                                  ├─ FFmpeg decode ──► VideoWidget (Qt UI)
                                                                                  └─ Ros2Bridge ──────► ROS 2 Topic (/hm30/image_raw)

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Project Structure

hm_30_rtp_receiver/
├── CMakeLists.txt           Build system (CMake 3.19+)
├── main.cpp                 Entry point, CLI parsing, stylesheet loading
├── stream.sdp               RTP stream descriptor (port patched at runtime)
│
    ├── src/
    │   ├── core/
    │   │   ├── app_config.h     Compile-time constants
    │   │   ├── stream_decoder.h Async H.264 decode worker (QThread)
    │   │   └── stream_decoder.cpp
    │   ├── ros2/
    │   │   ├── ros2_bridge.h    ROS 2 image publisher (Optional, conditionally compiled)
    │   │   └── ros2_bridge.cpp
    │   └── ui/
    │       ├── dashboard.h      Main window
    │       ├── dashboard.cpp
    │       ├── video_widget.h   Pure display canvas (QPainter)
    │       └── video_widget.cpp
│
├── resources/
│   ├── resources.qrc        Qt resource bundle (embeds style.qss)
│   └── style.qss            Dark theme with dynamic-property selectors
│
├── cmake/
│   └── version.h.in         CMake version header template
│
└── docs/
    ├── ARCHITECTURE.md      Data flow, class diagram, threading model
    └── BUILDING.md          Prerequisites, build modes, install, troubleshooting

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CLI Options

Usage: hm30_rtp_receiver [options]

Options:
  -h, --help              Display help
  -v, --version           Display version
  -u, --url <url>         Stream URL to connect to (default: udp://0.0.0.0:5600)
  --headless              Run without the GUI (useful for ROS 2 background publisher)

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ROS 2 Integration

This application natively supports ROS 2. If ROS 2 is sourced before building, it will automatically compile the Ros2Bridge and publish frames to /hm30/image_raw.

# 1. Source ROS 2
source /opt/ros/humble/setup.bash

# 2. Build
cd build && cmake .. && make -j$(nproc)

# 3. Run Headless Publisher
./hm30_rtp_receiver --headless --url "udp://0.0.0.0:5600"

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Architecture Summary

The application uses a two-thread model:

• UI thread — Qt event loop, VideoWidget painting, dashboard status refresh (2 Hz)
• Worker thread (StreamDecoder : QThread) — FFmpeg demux → H.264 decode → YUV→RGB conversion → emit frameReady(QImage)

All cross-thread communication uses Qt's queued signal/slot mechanism. See docs/ARCHITECTURE.md for the full data-flow diagram and class relationships.

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Comparison: RTP vs RTSP

Feature	RTSP Dashboard	RTP Receiver (this)
Transport	RTSP over UDP (client)	Raw RTP/UDP (passive)
Stream initiation	Client-pull	Server-push
Negotiation	RTSP + auto SDP	SDP file (manual)
RTSP handshake cost	Yes	None
Latency	Low	Lower

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Building in Debug Mode (ASAN/UBSan)

mkdir -p build_debug && cd build_debug
cmake .. -DCMAKE_BUILD_TYPE=Debug
make -j$(nproc)

See docs/BUILDING.md for full instructions.