When video is compressed each new frame (A frame is a still image in a video. Frames are rapidly drawn one by one to the computer screen to create the illusion of movement.) of a video isn't stored. Instead key frames (normal frames) and the movement of pixels each frame between the key frames are stored. This allows the video's file size to be much smaller as it only has to store what has changed each frame instead of every new frame.
Data moshing is when you take the movement frames from one video and and put them in another video. This creates a warp-y glitch-y effect. The above video was created using this effect with a video of Shia Labeouf and a rose blossoming.
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