The Netscape Loop Extension

DEC 15 1995 · 12:00

A 22 frame looping butterfly, the type of infinite loop that the NETSCAPE2.0 application extension made the default behavior of every web GIF. Place: Netscape Communications, Mountain View, California Figures: Netscape Navigator 2.0 engineering team · the unnamed engineer who picked the bytes GIF89a (see [[gif89a-released-1989]]) allows multiple image frames in a single file, with per-frame delays. What it does not define is whether the sequence plays once and stops, or loops forever. Netscape's engineers, preparing Navigator 2.0 for release, need a default behavior and a way to override it. They use the format's application-extension-block mechanism to invent one. The bytes: 21 FF 0B NETSCAPE2.0 03 01 LOW HIGH 00. The application identifier is the literal ASCII string NETSCAPE2.0, eleven bytes long. The two-byte loop count is little-endian: 0000 means loop forever, any other value means loop exactly N times. Netscape Navigator 2.0 ships in December 1995 with this extension implemented. Every other browser follows. Video: Navigator 2.x, the build that first honored the NETSCAPE2.0 application extension and let GIFs loop forever.