Digital videos are a representation of moving visual images encoded as digital data, allowing for easier editing and distribution compared to analog videos recorded on film reels. High definition refers to the number of pixels in a video image, with higher definitions like 4K allowing for clearer images. 3D videos add depth perception by processing two slightly different images for the left and right eyes. The internet has changed media promotion through online marketing and distribution, though piracy remains a disadvantage. On-demand services allow viewers to watch TV and movies whenever they want through streaming or downloads.