Virtual Display for Linux

Turn your Android tablet into a secondary display for Linux via USB. Like SuperDisplay or Duet Display, but open source and built natively for Linux.

I wanted a way to extend my Linux desktop workspace using the high-quality screen of my Android tablet, but existing solutions like VNC were too laggy, and commercial options like SuperDisplay didn’t support Linux native USB connections reliably. So, I built my own solution using EVDI (the same technology behind DisplayLink) and low-latency USB streaming.

Key Features

• Ultra Low Latency: Achieves ~20-40ms glass-to-glass latency via USB Type-C.
• High Resolution: Supports resolutions up to 4K at 120Hz.
• Plug & Play: Uses ADB/USB for a reliable, wired connection—no WiFi lag.
• Hardware Acceleration: leverages NVENC, VAAPI, and QSV for near-zero CPU usage on the host.
• Native Linux Integration: Uses the EVDI kernel module to create a genuine monitor interface in your OS (GNOME/KDE sees it as a real connected display).

How It Works

The system consists of two main components: a C++ host service on Linux and a Kotlin client app on Android.

Application Architecture

1. screen Capture (EVDI): The host creates a virtual framebuffer using the EVDI kernel driver. Linux desktop environments treat this as a standard physical monitor.
2. Encoding (FFmpeg): The pixel data from EVDI is captured and encoded into a H.264/HEVC stream using hardware-accelerated encoders (NVENC/VAAPI).
3. Transport (ADB/USB): The encoded stream is sent over a raw USB socket connection established via ADB port forwarding.
4. Decoding (Android): The Android app uses the native MediaCodec API to decode the video stream directly to a SurfaceView with minimal buffering.

graph LR
    subgraph Linux Host
    A[EVDI Buffer] -->|Capture| B[FFmpeg Encoder]
    B -->|H.264 Stream| C[USB Transport]
    end
    
    subgraph Android Tablet
    C -->|Raw Stream| D[MediaCodec Decoder]
    D -->|Render| E[Screen]
    end

Performance Metrics

Metric	Result
Capture FPS	50+ FPS
Encoding Latency	~7ms (NVENC)
Transport Latency	~1-3ms (USB)
Tested Resolution	Up to 2960x1820

Project Structure

The project is organized into two distinct codebases:

• libvirtualdisplay/: The Linux host library written in C++17. It handles the interaction with the EVDI kernel module, manages the FFmpeg encoding pipeline, and handles the USB socket communication.
• android-client/: The viewer application written in Kotlin. It handles device discovery, stream negotiation, and efficient hardware decoding.

Roadmap

• Phase 1: Core EVDI Integration & Framebuffer capture.
• Phase 2: Hardware Accelerated Encoding (NVENC/VAAPI).
• Phase 3: Stable USB Transport protocol.
• Phase 4: Reverse Input Injection (using the tablet touchscreen to control the mouse).
• Phase 5: Audio tunneling (send PC audio to tablet speakers).

---

This project is currently in active development. You can follow the progress or contribute on GitHub.