strings -n 8 unknown.idx Reveals embedded metadata or filenames. | Format | Use Case | Pros | Cons | |--------|----------|------|------| | .idx | Custom binary index | Fast, compact, seekable | Proprietary, opaque | | .ndx (Windows Help) | Compiled index | Rich metadata | Outdated | | .fti (Full-text) | Document search | Supports stemming | Larger file size | | .sha1 (Forensics) | Hash-only | Verifiable | No positional data |
Executive Summary An .idx file is not a single file type but a generic extension used to denote an index file . Its core purpose is to act as a roadmap or lookup table that allows software to find specific data within a larger, often sequential, primary data file without scanning the entire file. While the extension is consistent, its internal structure varies wildly depending on the application—from video subtitles to database keys and game archives. Core Concept: The Index Pattern In computing, an index separates location from data . Without an index, finding a record in a 10GB file requires reading from byte 0 to the target. With an index, you consult a small .idx file that says: "Search term 'X' starts at byte position 4,502,891" . what is an idx file
| Offset | Size | Field | Description | |--------|------|-------|-------------| | 0x00 | 4 bytes | Magic Number | 0x49445800 ("IDX\0") for validation | | 0x04 | 4 bytes | Version | 1, 2, 3 (determines field sizes) | | 0x08 | 8 bytes | Record Count | Number of index entries | | 0x10 | 2 bytes | Key Length | Bytes per key (e.g., 255) | | 0x12 | 2 bytes | Offset Length | Bytes per pointer (usually 4 or 8) | | 0x14... | Variable | Index Entries | [Key][Offset] repeated | strings -n 8 unknown
An .idx file is the index at the back of a textbook (pointing to page numbers), while the primary data file is the chapters themselves . Common Contexts & Structures 1. Video Subtitles (VobSub) Primary File: .sub (bitmap images) Idx Role: Timecode-to-position map. Internal Format (Plain Text): While the extension is consistent, its internal structure