HDMI Sniffer Project

Problem Statement

Traveling video artists and VJs frequently encounter HDMI connectivity issues at venues that are difficult to diagnose and troubleshoot in real-time. These issues manifest in two critical ways:

1. Initial Connection Failures: Unable to establish a stable HDMI connection with venue equipment (projectors, video routers, switchers) due to EDID incompatibilities or negotiation failures
2. Connection Dropouts During Performance: HDMI connections that fail mid-performance due to timing sync issues, signal retraining, or other protocol-level problems

Currently, video artists have limited visibility into these problems and lack portable, affordable tools to diagnose HDMI issues in the field. This project aims to develop open-source, cost-accessible hardware tools to monitor and diagnose HDMI connections.

Proposed Solution

Two complementary devices built from off-the-shelf components:

Device 1: EDID Reader/Manager

Purpose: Pre-connection diagnostics and EDID management
Function: Plugs into venue HDMI equipment (projectors, routers, etc.) to read and display supported EDID modes, with capability to inject custom EDID for compatibility
Use Case: Allows VJs to verify compatibility, configure output settings appropriately, and work around problematic venue EDIDs
Inspiration: HDMI dummy plug reprogramming via Raspberry Pi I2C

Device 2: Inline Connection Monitor

Purpose: Real-time connection monitoring and protocol analysis
Function: Sits inline between video source and display to monitor HDMI signal health, DDC/I2C traffic, and protocol-level events during performance
Use Case: Logs timing, sync, retraining, HDCP handshake events, and CEC traffic to diagnose intermittent connection issues
Inspiration: HDMI-over-IP extenders (Lenkeng), CEC sniffers, DDC traffic analysis tools

R&D Areas

Hardware Architecture

• EDID Reader/Manager: Raspberry Pi with I2C access (address 0x50) for reading/writing EDID data
  • Evaluate HDMI dummy plug modification approach (reprogrammable EEPROM)
  • Consider EDID injection/override capabilities for compatibility fixes
  • Research multi-bank EDID storage (see commercial devices: 5-40 banks)
• Inline Monitor: Research HDMI pass-through or splitter-based solutions
  • Investigate Lenkeng HDMI-over-IP extenders as potential monitoring platform
  • Evaluate CEC-Tiny-Pro approach for DDC/CEC sniffer (zero additional hardware)
  • Consider HDMI breakout cables for I2C/CEC access without signal interruption
• Evaluate whether devices should be separate or combinable (leaning toward separate due to multi-connection monitoring needs)
• Component sourcing to maintain cost accessibility

EDID Reading and Management

• I2C-based EDID reading using i2c-tools (read-edid, get-edid)
• EDID parsing and validation (parse-edid, edid-decode)
• EDID generation for custom resolutions/timings (edid-generate)
• Safe EDID writing with verification (edid-checked-writer approach)
• Display supported resolutions, refresh rates, timings, and vendor info
• EDID override/injection for problematic displays

Display & Interface

• EDID Reader: On-screen display showing supported modes, timings, manufacturer data
• Inline Monitor: On-screen display + data logging capability (SD card, USB, or network)
• Design for both technical and non-technical users with minimal learning curve
• Standalone operation (no computer required for monitoring)
• Consider USB interface for configuration and firmware updates

HDMI Protocol Analysis

• DDC (Display Data Channel): I2C bus monitoring (address 0x50 for EDID, 0x37 for DDC/CI)
  • Monitor VCP (VESA Control Protocol) feature codes
  • Log DDC/CI transactions for debugging
  • Detect EDID read failures or corruption
• CEC (Consumer Electronics Control): Pin 13 monitoring
  • Passive sniffing of CEC commands
  • Log device discovery and control messages
• TMDS (Transition-Minimized Differential Signaling): Signal quality monitoring
  • Clock signal synchronization and drift detection
  • Signal integrity and jitter analysis
  • Pixel clock frequency verification (25.2MHz to 297MHz range)
• HDCP (High-bandwidth Digital Content Protection):
  • Handshake monitoring and failure detection
  • Authentication event logging (without key extraction)
• Hot-plug detect (HPD) event tracking
• Signal retraining event detection and logging
• Cable integrity and signal quality metrics
• InfoFrame packet analysis (AVI, Audio, Vendor-Specific)

Common Failure Modes to Address

• Resolution negotiation failures (EDID incompatibilities)
• HDCP handshake issues
• Signal degradation over cable length
• Timing/sync drift during extended operation
• Vendor-specific projector/router compatibility issues
• Intermittent connection dropouts
• DDC/I2C communication failures
• CEC conflicts between devices
• Duplicate serial numbers for sinks confusing MadMapper

Data Logging & Analysis

• What metrics to log for the inline monitor
  • HPD events with timestamps
  • HDCP authentication attempts/failures
  • Signal retraining events
  • DDC/I2C transaction logs
  • CEC command sequences
  • Resolution/timing changes
• Log format: structured text (CSV/JSON) or binary
• Storage: SD card or USB flash drive
• Real-time vs. post-performance analysis tools
• Visualization of connection health over time
• Export compatibility with standard analysis tools

Reading EDID from Command Line

These are existing methods to read EDID information on different platforms. Our project aims to provide a portable, standalone alternative for field use.

Linux

Using read-edid (recommended):

# Install tools
sudo apt-get install read-edid

# Read and parse EDID
sudo get-edid | parse-edid

Using ddcutil:

# Install
sudo apt-get install ddcutil

# Detect monitors
ddcutil detect

# Read EDID
ddcutil --display 1 getvcp known

Using xrandr (for connected displays):

# List connected displays
xrandr --verbose

# Get detailed output
xrandr --prop

Direct from sysfs:

# Find EDID in sysfs
find /sys/devices -name edid

# Read and decode EDID
cat /sys/class/drm/card0-HDMI-A-1/edid | edid-decode

Raspberry Pi Specific

The Raspberry Pi has special HDMI configuration capabilities through its boot configuration system.

Reading EDID on Raspberry Pi:

# Get current EDID
tvservice -d /tmp/edid.dat
edidparser /tmp/edid.dat

# Or use standard Linux tools
sudo get-edid > edid.bin
parse-edid < edid.bin

Boot Configuration (/boot/firmware/config.txt or /boot/config.txt):

# Force specific HDMI mode
hdmi_group=2        # 1=CEA (TV), 2=DMT (Monitor)
hdmi_mode=82        # 1080p 60Hz

# Force HDMI output even if no display detected
hdmi_force_hotplug=1

# Boost HDMI signal (0-11, default 5)
config_hdmi_boost=7

# Ignore EDID and use safe mode
hdmi_safe=1

# Custom EDID file override
hdmi_edid_file=1
hdmi_edid_filename=custom_edid.dat

Common HDMI modes:

• Mode 4: 720p 60Hz
• Mode 16: 1080p 60Hz
• Mode 82: 1080p 60Hz (DMT)
• Mode 97: 1080p 60Hz (reduced blanking)

Useful Raspberry Pi commands:

# Show current HDMI status
tvservice -s

# List supported modes
tvservice -m CEA
tvservice -m DMT

# Set specific mode
tvservice -e "CEA 16"  # 1080p 60Hz

# Read I2C EDID directly (requires i2c-tools)
sudo i2cdetect -y 2
sudo i2cdump -y 2 0x50

I2C Access on Raspberry Pi:

The Raspberry Pi exposes I2C buses that can be used to read EDID:

• I2C-0, I2C-1: Internal (used for HATs, camera, etc.)
• I2C-2: HDMI DDC (EDID at address 0x50)

Enable I2C in /boot/firmware/config.txt:

dtparam=i2c_arm=on

macOS

Using system_profiler:

# Get display information
system_profiler SPDisplaysDataType

# More detailed output
ioreg -lw0 | grep IODisplayEDID

Extracting and decoding EDID:

# Get raw EDID (requires parsing ioreg output)
ioreg -lw0 -r -c "IODisplayConnect" | \
  grep -A 5 "IODisplayEDID" | \
  grep "IODisplayEDID" | \
  sed 's/.*<\(.*\)>/\1/' | \
  xxd -r -p > edid.bin

# Decode with edid-decode (install via Homebrew)
brew install edid-decode
edid-decode edid.bin

Using third-party tools:
BetterDisplay - https://github.com/waydabber/BetterDisplay
DisplayMenu - https://apps.apple.com/us/app/display-menu/id549083868
SwitchResX - https://www.madrau.com/

Windows

Using PowerShell:

# Get monitor information
Get-WmiObject WmiMonitorID -Namespace root\wmi | 
  Format-List *

# Get EDID data
Get-WmiObject -Namespace root\wmi -Class WmiMonitorDescriptorMethods |
  ForEach-Object {
    $_.WmiGetMonitorRawEEdidV1Block(0)
  }

Using Command Prompt with WMIC:

wmic desktopmonitor get /format:list
wmic path WmiMonitorID get /format:list

Registry method:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\DISPLAY\

EDID is stored as binary data under each display's Device Parameters key.

IOS

This app may have some utility - https://apps.apple.com/us/app/genr8/id6751822886
IOS UIKit provides very limited display enumearaton capabilities. - https://developer.apple.com/documentation/uikit/uiscreen

Third-party tools:

• MonitorInfoView (NirSoft) - Free utility
• Custom Resolution Utility (CRU) - Includes EDID editor
• EDID Reader - Simple EDID extraction tool

Project Status

Currently in R&D phase. This repository will document research findings, prototype designs, and eventually provide hardware schematics and software for building these tools.

Resources and References

Existing Tools and Projects

Hardware EDID Tools:

• Raspberry Pi EDID modification tutorial - Reprogramming HDMI dummy plug I2C EEPROM
• CEC-Tiny-Pro - Arduino HDMI CEC sniffer requiring zero additional hardware
• hdmi-sniff - Python DDC traffic sniffer using Bus Pirate

Software Utilities:

• read-edid - get-edid and parse-edid tools for Linux
• ddcutil - Comprehensive DDC/CI monitor control utility
• edid-checked-writer - Python I2C EDID writer with verification
• edid-generate - Programmatic EDID generation
• linuxhw/EDID - Database of 141,906+ decoded EDIDs

Commercial Reference Devices:

• HDFury Dr HDMI (1080p) and Dr HDMI 4K - Multi-bank EDID managers
• Geffen DisplayPort Detective Plus - DisplayPort EDID manager with sink sniffing

Protocol Documentation:

• HDMI Protocols Demystified - Comprehensive technical overview
• hdl-util/hdmi - FPGA HDMI implementation with pixel clock tables
• EDID Fundamentals - Explanation of EDID fields

Interesting Approaches:

• Lenkeng HDMI-over-IP reverse engineering - Potential platform for inline monitoring
• Cheap HDMI capture for Linux - Using Lenkeng devices with libpcap

Key Technical Details

I2C Addresses:

• 0x50: EDID EEPROM
• 0x37: DDC/CI (Monitor Control)

HDMI Pins:

• Pin 13: CEC (Consumer Electronics Control)
• Pin 15: SCL (I2C Clock)
• Pin 16: SDA (I2C Data)
• Pin 19: HPD (Hot Plug Detect)

Pixel Clock Frequencies:

• 640×480 @ 60Hz: 25.2 MHz
• 1920×1080 @ 60Hz: 148.5 MHz
• 3840×2160 @ 60Hz: 297 MHz

Contributing

This is an early-stage research project. Feedback, suggestions, and contributions are welcome as we explore solutions to HDMI connectivity challenges in live performance contexts.

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Target Users: Video artists, VJs, live visual performers, AV technicians
Design Principles: Cost-accessible, portable, user-friendly, open-source