SlipStream

Low-latency remote desktop streaming over WebRTC with hardware-accelerated video encoding.

Overview

SlipStream captures the Windows desktop using the Windows Graphics Capture API and encodes frames in real-time using NVIDIA NVENC. Video and audio are streamed to web browsers via WebRTC data channels with DTLS encryption. The client renders frames using WebGL2 and decodes video/audio using the WebCodecs API.

Architecture

┌──────────────────────────────────────────────────────────────────────────────┐
│                              SERVER (Windows)                                │
├──────────────────────────────────────────────────────────────────────────────┤
│  Screen Capture          Encoder              WebRTC              Audio      │
│  ┌──────────────┐     ┌──────────────┐    ┌──────────────┐     ┌──────────┐  │
│  │ WGC API      │───▶│ NVENC        │───▶│ Data Channel │◀──▶│ WASAPI   │  │
│  │ D3D11 Fence  │     │ H.264 / AV1  │    │ libdatachan  │     │ Opus     │  │
│  │ 6-tex pool   │     │ FFmpeg       │    │              │     │ 96 kbps  │  │
│  └──────────────┘     └──────────────┘    └──────────────┘     └──────────┘  │
│                                                │                             │
│                            ┌───────────────────┼───────────────────┐         │
│                            │      HTTPS Server (port 443)         │          │
│                            │   cpp-httplib + OpenSSL              │          │
│                            │   JWT Auth + Rate Limiting           │          │
│                            └───────────────────┼───────────────────┘         │
└────────────────────────────────────────────────┼─────────────────────────────┘
                                                 │
                            WebRTC (UDP 50000-50020)
                                                 │
┌────────────────────────────────────────────────┼─────────────────────────────┐
│                              CLIENT (Browser)                                │
├──────────────────────────────────────────────────────────────────────────────┤
│  ┌──────────────┐     ┌──────────────┐    ┌──────────────┐     ┌──────────┐  │
│  │ VideoDecoder │───▶│ WebGL2       │    │ AudioDecoder  │───▶│ Worklet  │  │
│  │ HW or SW     │     │ Letterbox    │    │ Opus         │     │ RingBuf  │  │
│  └──────────────┘     └──────────────┘    └──────────────┘     └──────────┘  │
│                                                                              │
│  Input Handler ──────▶ Mouse/Keyboard ──────▶ Data Channel ──────▶ Server  │
└──────────────────────────────────────────────────────────────────────────────┘

Features

• Dual Codec Support - H.264 and AV1 via NVIDIA NVENC
• Hardware Decoding - WebCodecs API with automatic HW/SW fallback
• System Audio - WASAPI loopback capture with Opus encoding
• Multi-Monitor - Live monitor switching with optional tabbed UI
• Clipboard Sync - Bidirectional text clipboard (Ctrl+C/V)
• Relative Mouse - Pointer lock mode for games and full-screen apps
• Session Auth - PBKDF2-SHA256 password hashing with JWT tokens
• Rate Limiting - Protection against brute-force attacks
• Auto SSL - Self-signed certificate generation on first run
• Debug Stats - Real-time performance overlay

Requirements

Server

Component	Requirement
OS	Windows 10/11 64-bit (build 1903+)
GPU	NVIDIA GPU with NVENC support
IDE	Visual Studio 2022 with C++20 Desktop workload
Package Manager	vcpkg

Client

Component	Requirement
Browser	Chrome 94+, Edge 94+, Firefox 98+
APIs	WebRTC, VideoDecoder, AudioDecoder, WebGL2

Quick Start

1. Install vcpkg

git clone https://github.com/microsoft/vcpkg.git C:\vcpkg
cd C:\vcpkg
.\bootstrap-vcpkg.bat
.\vcpkg integrate install

2. Build

build.bat

Output: build\bin\Release\SlipStream.exe

3. Run

run.bat

On first run:

• Prompts for username (3-32 alphanumeric characters)
• Prompts for password (8+ characters with at least one letter and digit)
• Generates self-signed SSL certificate (server.crt, server.key)
• Saves hashed credentials to auth.json

4. Connect

Open browser to https://<HOST_IP>:443 and log in with your credentials.

Note: Self-signed certificate will trigger a browser warning. Click through to proceed.

Network Configuration

Port	Protocol	Purpose
443	TCP	HTTPS server and WebRTC signaling
50000-50020	UDP	WebRTC media transport

Firewall

netsh advfirewall firewall add rule name="SlipStream HTTPS" dir=in action=allow protocol=tcp localport=443
netsh advfirewall firewall add rule name="SlipStream WebRTC" dir=in action=allow protocol=udp localport=50000-50020

Security

Password Storage

Parameter	Value
Algorithm	PBKDF2-HMAC-SHA256
Iterations	600,000
Salt	16 bytes (random)
Key Length	32 bytes

Passwords are never stored in plain text. Only the salt and derived hash are saved in auth.json.

Rate Limiting

Threshold	Action
5 failed attempts in 15 min	30-minute IP lockout
Successful login	Clears attempt counter

JWT Sessions

Parameter	Value
Algorithm	HS256
Issuer	slipstream
Expiry	24 hours
Storage	HttpOnly cookie

SSL Certificates

Auto-generated on first run:

• 2048-bit RSA key
• 10-year validity
• Subject Alt Names: localhost, 127.0.0.1, 0.0.0.0

To use custom certificates, replace server.crt and server.key before starting.

API Endpoints

Endpoint	Method	Auth	Description
/	GET	No	Web client HTML
/styles.css	GET	No	Stylesheet
/js/*.js	GET	No	JavaScript modules
/api/auth	POST	No	Login with {username, password}
/api/session	GET	Cookie	Validate current session
/api/logout	POST	No	Clear session cookie
/api/offer	POST	Cookie	WebRTC SDP offer exchange

Video Pipeline

Capture

Component	Detail
API	Windows Graphics Capture
Texture Pool	6 textures with D3D11 fence sync
Frame Buffer	4-frame ring buffer
Cursor	Captured in stream
Border	Disabled (if supported)

Encoding

Setting	H.264	AV1
Encoder	h264_nvenc	av1_nvenc
Preset	P1 (fastest)	P1 (fastest)
Tune	Ultra-low latency	Ultra-low latency
Rate Control	VBR	VBR
CQ Level	23	28
Keyframe Interval	2 seconds	2 seconds
B-Frames	0	0
Color Space	BT.709	BT.709
Color Range	Full (JPEG)	Full (PC)

Bitrate Formula: 0.18085 × width × height × fps bps

Example: 1920×1080 @ 60fps = ~22.5 Mbps

Transport

Parameter	Value
Chunk Size	1400 bytes max
Header Size	21 bytes
Video Buffer	256 KB threshold
Max Queue	3 frames worth
Delivery	Unreliable, unordered

Video Packet Header (21 bytes)

Offset	Size	Field	Description
0	8	timestamp	Capture timestamp (microseconds)
8	4	encodeTimeUs	Encode duration
12	4	frameId	Frame sequence number
16	2	chunkIndex	Current chunk index
18	2	totalChunks	Total chunks in frame
20	1	frameType	1=keyframe, 0=delta

Audio Pipeline

Capture

Parameter	Value
API	WASAPI Loopback
Mode	Shared
Sample Rate	48,000 Hz (resampled if needed)
Channels	Stereo (max 2)
Frame Duration	10 ms (480 samples)

Encoding

Parameter	Value
Codec	Opus
Application	Restricted Low Delay
Bitrate	96 kbps
Complexity	3
Signal Type	Music

Transport

Parameter	Value
Audio Buffer	128 KB threshold
Max Queue	4 packets
Delivery	Unreliable, unordered

Audio Packet Header (16 bytes)

Offset	Size	Field	Description
0	4	magic	0x41554449 ("AUDI")
4	8	timestamp	Capture timestamp
12	2	samples	Sample count
14	2	dataLength	Opus payload size

Client Playback

Component	Detail
Decoder	AudioDecoder (WebCodecs)
Processor	AudioWorklet
Buffer	Ring buffer (2400 samples)
Target Latency	480 samples (~10ms)
Max Buffer	1200 samples (~25ms)

Input Protocol

Mouse Move Absolute (12 bytes)

Offset	Size	Field
0	4	magic (0x4D4F5645)
4	4	x (float 0-1)
8	4	y (float 0-1)

Mouse Move Relative (8 bytes)

Offset	Size	Field
0	4	magic (0x4D4F5652)
4	2	dx (int16)
6	2	dy (int16)

Mouse Button (6 bytes)

Offset	Size	Field
0	4	magic (0x4D42544E)
4	1	button (0-4)
5	1	action (1=down, 0=up)

Button mapping: 0=left, 1=right, 2=middle, 3=X1, 4=X2

Mouse Wheel (8 bytes)

Offset	Size	Field
0	4	magic (0x4D57484C)
4	2	deltaX (int16)
6	2	deltaY (int16)

Keyboard (10 bytes)

Offset	Size	Field
0	4	magic (0x4B455920)
4	2	keyCode (JS keyCode)
6	2	scanCode
8	1	action (1=down, 0=up)
9	1	modifiers

Modifiers: Ctrl=1, Alt=2, Shift=4, Meta=8

Clipboard Data (8 + N bytes)

Offset	Size	Field
0	4	magic (0x434C4950)
4	4	length
8	N	UTF-8 text (max 1MB)

Rate Limits

Type	Max per Second
Mouse moves	500
Clicks	50
Keystrokes	100

Blocked Inputs

• Windows key (left/right)
• Ctrl+Alt+Delete

WebRTC Data Channels

Channel	Ordered	MaxRetransmits	Purpose
control	Yes	3	Commands, ping, monitor list
video	No	0	Video frames
audio	No	0	Audio packets
input	Yes	3	Mouse/keyboard events

Client Modules

File	Purpose
state.js	Shared state, constants, metrics, clock sync
network.js	HTTP auth, WebRTC signaling, data channels
renderer.js	WebGL2 rendering with aspect ratio letterboxing
media.js	VideoDecoder, AudioDecoder, AudioWorklet
input.js	Mouse/keyboard capture, batching, pointer lock
ui.js	Settings panel, fullscreen, tabbed mode, stats

Clock Synchronization

• Ping interval: 200ms
• Sample count: 8
• Offset calculation: Median filter
• RTT estimation: Median of samples

Frame Handling

Parameter	Value
Max buffered frames	8
Frame timeout	200ms
Max frame age	50ms
Decode queue limit	6

UI Features

Settings Panel

Access by clicking the right edge of the screen:

• Logout - Disconnect and clear session
• Fullscreen - Enter fullscreen with keyboard lock (Escape captured)
• Audio - Toggle system audio playback
• Monitor - Switch between displays
• Frame Rate - 15/30/60/120/144 or custom (1-240)
• Codec - H.264 or AV1 (shows HW/SW status)
• Tabbed Mode - Monitor tabs at top of screen
• Debug Stats - Real-time performance overlay
• Relative Mouse - Pointer lock mode for gaming
• Clipboard Sync - Enable Ctrl+C/V synchronization

Tabbed Mode

When enabled, displays a tab strip showing all monitors with:

• Monitor name (friendly name from EDID)
• Resolution
• Primary indicator (star icon)

Debug Stats Overlay

Real-time metrics display:

Section	Metrics
Throughput	FPS (actual/target), bitrate, resolution, codec
Latency	RTT, frame age
Jitter	Frame interval mean, std dev
Decode	Time, queue size, HW acceleration status
Render	Time, frame count
Network	Packet count, average size
Drops	Dropped, timeout, late, decode errors
Audio	Packets, decoded, buffer health, underruns, overflows
Input	Mouse moves, clicks, keystrokes
Session	Uptime, total frames, total data

Server Threads

Thread	Priority	Purpose
Main	Above Normal	HTTPS server
Encoder	Time Critical	Frame encoding loop
Audio	Highest	Audio capture and encoding

Dependencies

Managed via vcpkg (vcpkg.json):

Package	Purpose
libdatachannel	WebRTC implementation
cpp-httplib[openssl]	HTTPS server
nlohmann-json	JSON parsing
opus	Audio encoding
openssl	Cryptography, SSL/TLS
ffmpeg[nvcodec,avcodec]	Video encoding
jwt-cpp	JWT token handling

Building

Standard Build

build.bat

Installer Build

build_installer.bat

Creates SlipStream-1.0.0-win64.exe (NSIS) or .zip (fallback).

Troubleshooting

Problem	Solution
vcpkg not found	Set VCPKG_ROOT or install to C:\vcpkg
NVENC unavailable	Requires NVIDIA GPU with NVENC support
Connection refused	Check firewall for TCP 443, UDP 50000-50020
Black screen	Wait for keyframe or click to focus
No audio	Click "Enable" in settings panel
Input not working	Click the video canvas to capture focus
Certificate warning	Expected with self-signed cert

Known Limitations

• Windows server only
• Single client connection (new client kicks existing)
• NVIDIA GPU required for encoding
• No file transfer

License

Business Source License (Personal-Online / No-Company) v1.1

Personal use permitted. Commercial use requires separate license.

See LICENSE.txt for full terms.

Copyright

(c) 2025-2026 Daniel Chrobak. All rights reserved.