efm-decoder-data

EFM Data24 to Binary Data Decoder

Overview

efm-decoder-data converts Data24 sections into ECMA-130 compliant binary data sectors. This tool handles data-mode EFM decoding for applications like Domesday LaserDiscs and CD-ROM data, performing Reed-Solomon Product Code (RSPC) error correction and producing raw binary output.

Usage

efm-decoder-data [options] <input.d24> <output.bin>

Options

• -h, --help - Display help information
• -v, --version - Display version information
• -d, --debug - Show debug output
• -q, --quiet - Suppress info and warning messages
• --output-metadata - Output bad sector map metadata file
• --show-rawsector - Show raw sector frame data
• --show-rawsector-debug - Show Data24 to raw sector decoding debug
• --show-sector-debug - Show raw sector to sector decoding debug
• --show-sector-correction-debug - Show sector correction debug
• --show-all-debug - Show all decoding debug

Arguments

• input - Input Data24 section file (from efm-decoder-d24)
• output - Output binary data file

Processing Pipeline

The decoding sequence performed by efm-decoder-data:

1. Data24 Sections → Input from efm-decoder-d24 (or stdin via Unix pipes, 2352 bytes per section)
2. Raw Sectors → Extract 2048-byte data sectors from each section
3. RSPC Error Correction → Reed-Solomon Product Code correction
4. Sector Validation → Mark sectors as valid or invalid
5. Binary Output → Continuous binary data stream

Unix Pipelining: efm-decoder-data supports stdin/stdout using -, enabling direct data extraction from EFM processing pipelines.

Technical Details

Data Format Conversion

• Input: Data24 sections (2352 bytes each, representing 1/75 second)
• Processing: Strip EFM parity and error correction overhead
• Output: Pure data sectors (2048 bytes each)
• Efficiency: ~87% data efficiency (2048/2352)

RSPC Error Correction

Implements Reed-Solomon Product Code correction according to ECMA-130:

• Q Parity: Outer code correction
• P Parity: Inner code correction
• Sector-level: All-or-nothing correction per 2048-byte sector
• Unscrambling: Data de-interleaving for error correction

Error Handling

Unlike audio decoding, data decoding is binary:

• Valid sectors: Fully corrected, guaranteed accuracy
• Invalid sectors: Uncorrectable, flagged in metadata
• No concealment: Corrupted data is not interpolated

Metadata Output

Bad Sector Map

When --output-metadata is specified, creates a text file listing invalid sector addresses:

28
29
30
31

Each number represents a 2048-byte sector that could not be corrected.

Format

• One sector address per line
• Addresses are sequential (starting from 0)
• Only invalid/uncorrectable sectors are listed
• Can be used by downstream tools for error handling

Pipeline Integration

Input Requirements

• Data24 sections from efm-decoder-d24
• CIRC-corrected data (first-stage error correction completed)

Common Workflows

Standard Data Extraction

# Complete pipeline for data using Unix pipes
efm-decoder-f2 input.efm - | efm-decoder-d24 - - | efm-decoder-data - output.bin --output-metadata

# Alternative: step by step with files
efm-decoder-f2 input.efm temp.f2
efm-decoder-d24 temp.f2 temp.d24  
efm-decoder-data temp.d24 output.bin --output-metadata

Domesday LaserDisc Workflow

# Extract data then verify VFS structure
efm-decoder-data domesday.d24 domesday.bin --output-metadata
vfs-verifier domesday.bin domesday_metadata.txt

Multi-Source Data Recovery

# Stack sources for better error correction
efm-stacker-f2 disc1.f2 disc2.f2 disc3.f2 stacked.f2
efm-decoder-d24 stacked.f2 stacked.d24
efm-decoder-data stacked.d24 recovered.bin --output-metadata

Output Verification

The extracted binary data can be verified using:

• vfs-verifier - For Domesday LaserDisc VFS structures
• Standard file analysis tools
• Checksum verification (if reference data available)