Unreal Engine 4 PAK

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PAK

• Format Type : Archive
  
• Endian Order : Little Endian
  
• Signature : None
  

Format Specifications

Uses ZLib, GZip, or Snappy Compression
FILE DATA
  for each file
    uint64 {8}       - null
    uint64 {8}       - Compressed Length (not including the file header fields or padding)
    uint64 {8}       - Decompressed Length
    uint32 {4}       - Compression Type (0=uncompressed, 1=ZLib, 2=GZip, 4=Snappy)
    byte {20}        - Unknown
    if (compressed){
      uint32 {4}       - Number of Compressed Blocks
      for each compressed block
        uint64 {8}       - Offset to the start of the compressed data block (relative to the start of the archive)
        uint64 {8}       - Offset to the end of the compressed data block (relative to the start of the archive)

      byte {1}         - null
      for each compressed block
        uint32 {4}       - Decompressed Length of thie block
        byte {X}         - File Data (ZLib Compression)

      byte {0-2047}    - null Padding to a multiple of 2048 bytes (sometimes, not always)
      }

    else if (uncompressed){
      uint32 {4}       - null
      byte {1}         - null
      byte {X}         - File Data
      byte {0-2047}    - null Padding to a multiple of 2048 bytes (sometimes, not always)
      }

DIRECTORY
  uint32 {4}       - Relative Directory Name Length (including null terminator) (10)
  byte {9}         - Relative Directory Name (../../../)
  byte {1}         - null Relative Directory Name Terminator
  uint32 {4}       - Number of Files
  for each file
    uint32 {4}       - Filename Length (including null terminator)
    byte {X}         - Filename
    byte {1}         - null Filename Terminator
    uint64 {8}       - File Offset
    uint64 {8}       - Compressed Length (not including the file header fields or padding)
    uint64 {8}       - Decompressed Length
    uint32 {4}       - Compression Type (0=uncompressed, 1=ZLib, 2=GZip, 4=Snappy)
    byte {20}        - Unknown
    if (compressed){
      uint32 {4}       - Number of Compressed Blocks
      for each compressed block
        uint64 {8}       - Offset to the start of the compressed data block (relative to the start of the archive)
        uint64 {8}       - Offset to the end of the compressed data block (relative to the start of the archive)

      byte {1}         - null
      uint32 {4}       - Decompressed Block Size (65536 if multiple blocks, otherwise the same as the decompressed length)
      }

    else if (uncompressed){
      uint32 {4}       - null
      byte {1}         - null
      }

FOOTER (44 bytes)
  uint32 {4}       - Magic Number ((bytes)225,18,111,90)
  uint32 {4}       - Version (3)
  uint64 {8}       - Directory Offset
  uint64 {8}       - Directory Length (not including FOOTER)
  byte {20}        - Unknown

MultiEx BMS Script

Not written yet.

Notes and Comments

• These files normally occur in path such as "\<game_name>\<build_name>\Content\Paks\<build_name>-WindowsNoEditor.pak"

Games

List of games using this file format:

• Little Nightmares II (PC) (*.PAK)

Compatible Programs

• UnrealPakTool
  

// TODO