XMP Specification September 2005 95 Embedding XMP Metadata in Application Files GIF 5 GIF In a GIF89a file, an XMP Packet is in an Application Extension (see the following figure). Its Application Identifier is 'XMP Data' and the Application Authenticator is 'XMP'. The Application Data consists of the XMP Packet, which must be encoded as UTF-8, followed by a 258-byte “magic” trailer, whose values are 0x01, 0xFF, 0xFE, 0xFD ....0x03, 0x02, 0x01, 0x00, 0x00. The final byte is the Block Terminator. XMP in GIF File Format: The XMP must be UTF-8-encoded, for the following reasons. GIF actually treats the Application Data as a series of GIF data sub-blocks. The first byte of each sub-block is the length of the sub-block’s content, not counting the first byte itself. To consume the Application 0 0x21 1 0xFF 0x0B 2 3 0 1 6 7 4 5 10 11 8 9 ‘X’ ‘M’ ‘P’ ‘ ’ ‘D’ ‘a’ ‘t’ ‘a’ ‘X’ ‘P’ ‘M’ 0x58 0x4D 0x50 0x20 0x44 0x61 0x74 0x61 0x58 0x50 0x4D 0x00 7 6 5 4 3 2 1 0 Field Name Type Extension Introducer Byte Extension Label Byte Block Size Byte Application Identifier 8 Bytes Application Authentication 3 Bytes XMP Packet, Byte Code must be encoded as UTF-8 0x01 0xFF 0xFE 0x00 0x01 ... “Magic trailer” Block Terminator Byte XMP Packet 258 Bytes