Screen Capture

Minimal Windows screen capture and real-time streaming sample. The sender captures the primary screen, JPEG-encodes the frame, GZip-compresses it, and streams it over TCP to a WinForms receiver that displays the image. Built with .NET 8.

Overview

• Transport: TCP with a simple length-prefixed framing. A UDP helper exists in Shared (for experiments) but is not used by the main path.
• Encoding: Full-screen capture → JPEG → GZip.
• UI: WinForms app (Receiver) renders frames in a PictureBox.

Project structure

• src/Shared
  • Sender: screen capture, JPEG encoding, GZip compression; includes a UDP send utility (sample)
  • Receiver: TCP receive helpers, GZip decompression, byte[] → Image
  • Packet: DTO for UDP framing (not used by the default TCP path)
• src/Sender: console app that sends frames to a target IP:Port in a loop
• src/Receiver: WinForms app that displays incoming frames
• Solution: screen.capture.sln

Protocol (wire format)

For each frame sent over TCP:

1. 5-byte header
   • 4 bytes: payload length (little-endian Int32)
   • 1 byte: compression flag (0x01 = compressed, 0x00 = uncompressed)
2. Payload: frame bytes (JPEG if uncompressed; GZip(JPEG) if compressed)

The sender currently always compresses (0x01). The receiver handles both modes. Default inter-frame delay is 10 ms, but actual FPS depends on hardware and network.

Requirements

• Windows 10 or later (WinForms + primary screen capture)
• .NET SDK 8.0+

Quick start

1. Build the solution

# Run at the repository root (where README.md resides)
dotnet build .\screen.capture.sln

2. Start the receiver

dotnet run --project .\src\Receiver\Receiver.csproj

• Default listen port: 8088
• To change the port: edit src/Receiver/App.config or src/Receiver/Properties/Settings.settings (key: ListenPort)

3. Start the sender

# Usage: dotnet run --project <csproj> -- <IP> <PORT>
dotnet run --project .\src\Sender\Sender.csproj -- 127.0.0.1 8088

• For same-machine tests use 127.0.0.1 or localhost.
• For cross-machine tests, use the receiver machine’s IP and allow the port through Windows Firewall.
• Press Esc in the sender console to stop the capture loop.

Features

• Primary screen capture (Screen.PrimaryScreen)
• JPEG + GZip to reduce bandwidth
• Simple TCP framing (length + compression flag)
• WinForms UI for real-time display

Limitations

• Windows-only (relies on WinForms and Screen.PrimaryScreen)
• No encryption/authentication (intended as a learning/demo project)
• Latency and dropped frames may occur depending on network conditions
• CPU usage can be high (tight loop capture + encode + compress)
• UDP send helper exists but the default demo path is TCP-based

Troubleshooting

• No image on the receiver
  • Ensure the receiver is running before the sender connects
  • Verify IP/Port match between sender and receiver
  • Allow the receiver’s listen port through Windows Firewall
• Slow transfer or high CPU usage
  • Increase the capture delay (DelayBetweenSendsMs in src/Sender/Program.cs)
  • Consider adjusting JPEG quality via a custom encoder (current code uses default Image.Save JPEG)
• Multi-monitor
  • Only Screen.PrimaryScreen is captured; extend to target a specific monitor/region if needed

Docs

• Roadmap: docs/ROADMAP.md
• Tasks: docs/TASK.md
• Contributing: docs/CONTRIBUTNG.md

Directory layout

src/
  Receiver/
  Sender/
  Shared/
screen.capture.sln

License

Licensed under the MIT License. See LICENSE.md for details.

Notes

• Built with .NET 8 (WinForms)
• Length prefix uses little-endian Int32
• Receiver default port: 8088 (App.config > userSettings > ListenPort)