Core Parsing Architecture

exiftool uses a streaming, zero-copy parsing architecture designed for performance and memory efficiency.

Pipeline Architecture

Input (File/Stream/Buffer)
         │
         ▼
Format Detection (Magic Bytes)
         │
         ▼
Format Parser (JPEG/PNG/WebP/AVIF-HEIF/TIFF-family RAW)
         │
         ▼
├── EXIF/TIFF Parser ──────► IFD Walking
├── XMP Parser ───────────► XML + RDF Parsing
├── IPTC Parser ──────────► Application Record Parsing
├── ICC Profile Parser ───► Tag Decoding
├── JUMBF Parser ──────────► Box Walking + CBOR
└── MakerNote Decoder ───► Vendor tag decoding (Canon, Nikon, Sony, Olympus, Panasonic, Pentax)
         │
         ▼
Composite Tag Computation
         │
         ▼
Output Normalization (JSON/CSV/Tabular)

Memory Design

• Zero-copy: tag values are Uint8Array views into the source buffer where possible — copy out before retaining
• Whole-buffer reads: files are read fully into memory; there is no streaming or partial-load mode
• No subprocesses: parsing happens in-process, one read() per file, no exiftool binary involved

Format Parsers

Each format has a dedicated parser plugin in src/format/:

Format	Parser	Key Features
JPEG	jpeg.ts	APP1 EXIF/XMP, APP13 IPTC, APP11 JUMBF, JFIF, MPF
PNG	png.ts	iTXt/tEXt/zTXt, eXIf, caBX (JUMBF)
WebP	webp.ts	VP8/VP8L, EXIF/XMP in VP8X
AVIF/HEIF	avif.ts	ISOBMFF boxes, Exif/XMP/ICC in meta
TIFF-family RAW	tiff-raw.ts	TIFF, DNG, CR2, NEF, ARW, ORF, RW2, PEF, ERF, DCR, SRW (read-only)

IFD Walking (TIFF/EXIF)

TIFF Header (8 bytes)
         │
         ▼
First IFD Offset ──────► IFD Entry Count (2 bytes)
                              │
                              ▼
                      IFD Entries (12 bytes each)
                              │
                              ├─► Tag ID (2 bytes)
                              ├─► Type (2 bytes)
                              ├─► Count (4 bytes)
                              └─► Value/Offset (4 bytes)
                              │
                              ▼
                      Next IFD Offset (4 bytes)

Coordinate Format

GPS coordinates use rational numbers (num/denom):

// Internal representation
GPSLatitude: [
  { num: 37, den: 1 },     // degrees
  { num: 45, den: 1 },     // minutes
  { num: 3025, den: 100 }  // seconds (30.25")
]

// Output formats
// DMS: "37° 45' 30.25" N"
// Decimal: 37.758403

Performance Characteristics

Measured on an M2 Max against the reference ExifTool 13.55 binary, 218 real-world JPEGs (~3.1 GB) read by a single process:

Metric	exiftool-ts	Reference exiftool
Batch read, one process	2.1 s (~10 ms/file)	3.9 s (~18 ms/file)
Cold CLI call, single file	~150 ms (node) / ~125 ms (bun)	~150 ms
Peak memory, same batch	~0.6–0.8 GB (V8 high-water, bounded)	~34 MB

The in-process win comes from having no subprocess and no interpreter startup per file; the memory cost comes from the JavaScript runtime's heap management.