The video itself can be regarded as a collection of photos. Video is composed of many pictures, but in addition, the video itself has several tracks, such as audio track and subtitle track, which requires different compression and packaging technologies for video and pictures. In fact, dynamic and static are not their essential differences, because video can also be static and the same picture can also be dynamic (for example, GIF animation is also a kind of picture). So the essential difference between video and pictures can be seen as: two multimedia files with different compression technologies. In addition, the video is three-dimensional, because there is time besides the plane image (here, three-dimensional does not refer to the 3D of stereoscopic movies, but refers to: video =x+y+z), and the picture =x+y, where x is the horizontal coordinate of pixels, y is the vertical coordinate of pixels, and z is the time).