efm-decoder-d24

EFM F2 Section to Data24 Section Decoder

Overview

efm-decoder-d24 takes F2 sections as input (from efm-decoder-f2) and decodes them into Data24 sections. This tool performs the critical CIRC error correction (C1 and C2) and unscrambling according to ECMA-130 specifications.

Data24 sections are an intermediate format that can be interpreted as either audio data (IEC 60908) or sector-based data (ECMA-130).

Usage

efm-decoder-d24 [options] <input.f2> <output.d24>

Options

• -h, --help - Display help information
• -v, --version - Display version information
• -d, --debug - Show debug output
• -q, --quiet - Suppress info and warning messages
• --show-f1 - Show F1 frame data
• --show-data24 - Show Data24 frame data
• --show-f2-debug - Show F2 to F1 decoding debug
• --show-f1-debug - Show F1 to Data24 decoding debug
• --show-all-debug - Show all debug options

Arguments

• input - Input F2 section file (from efm-decoder-f2)
• output - Output Data24 section file

Processing Pipeline

The decoding sequence performed by efm-decoder-d24:

1. F2 Sections → Input from efm-decoder-f2 (or stdin via Unix pipes)
2. F1 Sections → CIRC error correction applied
3. Data24 Sections → Byte order corrected, ready for final decoding

Unix Pipelining: efm-decoder-d24 supports stdin/stdout using -, allowing seamless integration in EFM processing pipelines.

Technical Details

CIRC Error Correction

The tool implements Cross-Interleaved Reed-Solomon Code (CIRC) error correction:

• C1 Correction: First level error correction
• C2 Correction: Second level error correction
• Unscrambling: Data de-interleaving according to ECMA-130

Data24 Format

Data24 sections consist of:

• 98 frames per section (representing 1/75th second)
• 24 bytes per frame (2352 bytes total per section)
• Corrected byte order (unlike F1 frames which have reversed byte order)
• Preserved section metadata from F2 input

Error Handling

The CIRC system can:

• Detect up to 4 symbol errors per codeword
• Correct up to 2 symbol errors per codeword
• Flag uncorrectable errors for concealment by downstream tools

Output Format

Data24 sections can be processed by either:

• efm-decoder-audio - For audio decoding (CD audio, LaserDisc digital audio)
• efm-decoder-data - For data decoding (Domesday LaserDiscs, CD-ROM data)

Performance Notes

• CIRC correction is computationally intensive
• Error correction effectiveness depends on input quality
• Heavily damaged sections may require multiple source stacking (efm-stacker-f2)