DisplayFlow/demo/windows_sender/README.md

# Windows Sender Demo

This is a simplified demo of the Windows Host sender for DisplayFlow.

It demonstrates:
1. Screen Capture using Desktop Duplication API (DXGI).
2. Hardware/Software H.264 Encoding using **FFmpeg** (switched from Media Foundation for better compatibility).
3. Network Transmission using UDP.

## Prerequisites

- Windows 10/11
- Visual Studio 2022 or later (with C++ Desktop Development)
- CMake 3.10+
- **FFmpeg Development Libraries** (Shared)
  - Ensure you have the `include` and `lib` directories.
  - Example path: `D:\tools\ffmpeg-8.0.1-full_build-shared`

## Build

1. Open a terminal (Developer Command Prompt for VS or PowerShell).
2. Navigate to this directory:
   ```cmd
   cd demo\windows_sender
   ```
3. Create a build directory:
   ```cmd
   mkdir build
   cd build
   ```
4. Configure and Build (Replace path with your FFmpeg location):
   ```cmd
   cmake .. -DFFMPEG_ROOT="D:/tools/ffmpeg-8.0.1-full_build-shared"
   cmake --build . --config Release
   ```
   *Note: If your FFmpeg is installed elsewhere, change the path accordingly.*

5. **Important**: Copy FFmpeg DLLs to the executable directory.
   - Copy `avcodec-*.dll`, `avutil-*.dll`, `swscale-*.dll`, `avformat-*.dll` from your FFmpeg `bin` directory to `demo\windows_sender\build\Release`.

## Run

Run the executable with optional arguments: Target IP, Port, and Output File.

```cmd
.\Release\WindowsSenderDemo.exe [TargetIP] [Port] [OutputFile]
```

### Examples

1. **Basic Streaming** (Default: 127.0.0.1:8888):
   ```cmd
   .\Release\WindowsSenderDemo.exe
   ```

2. **Specify Target**:
   ```cmd
   .\Release\WindowsSenderDemo.exe 192.168.1.100 8888
   ```

3. **Stream and Save to File** (for debugging):
   ```cmd
   .\Release\WindowsSenderDemo.exe 127.0.0.1 8888 debug.h264
   ```
   You can play the saved `debug.h264` using VLC player to verify the encoding quality.

## Implementation Details

- **ScreenCapture**: Uses `IDXGIOutputDuplication` to capture desktop frames.
- **VideoEncoder**: 
  - Uses **FFmpeg (libx264)** for encoding.
  - Performs **BGRA to YUV420P** color conversion using `libswscale`.
  - Configured for low latency (`zerolatency` tune, `ultrafast` preset).
- **NetworkSender**: Fragments the H.264 stream into UDP packets (MTU ~1400 bytes) and sends them to the target.

## Protocol

The demo uses a simple custom protocol for feasibility verification:
- **Packet Header** (Network Layer): `FrameID` (4B), `FragID` (2B), `TotalFrags` (2B).
- **Frame Header** (Application Layer, in first fragment/reassembled): `Timestamp` (8B), `Width` (4B), `Height` (4B), `Type` (4B), `Size` (4B).
- **Payload**: H.264 NAL units.