XVID; XMOV - MajickTek/XFF-SPEC GitHub Wiki

The eXtensible Video Format or eXtensible Movie format is something which I made up.

The idea is simple:

You have multiple images stored in one file, and a sound file to go on top. The sound is optional if you want to create something like a GIF. You have a certain number of "frames", which is each image. You iterate through these frames to create smooth animation. An algorithm is used to calculate how fast the images are iterated, and when the sound is played compared to which frame is showing.