Notice that most of the content from frame to frame remains the same, only the butterfly’s wings change slightly. Three sequential frames of video from Big Buck Bunny at 30 fps. A newscaster’s lips may move as they talk, and information may scroll along the bottom of the screen, but a large portion of the image is either the same, or very similar, from frame to frame. If you think of a typical video that you might watch online or on TV, a newscast for example, each frame of video is typically very similar to those that precede and follow it. In this blog post, I will scratch the surface by explaining general concepts of video compression.Īt its fundamental level, video compression works by finding and eliminating redundancies within an image or a sequence of images. How much time do you have? Deeply understanding the specifics of video compression requires years of study and is often the subject of research by graduate students in Computer Science or Mathematics. So in order to deliver video over the internet, or other fixed capacity medium (such as satellite or Blu-Ray discs), it is necessary to compress the video to more manageable bitrates (usually in the 1-20 Mbps range). For much of the world, residential internet services aren’t even capable of sustaining speeds near that. While sending video around at multiple gigabits per second may be feasible within a professional production facility, it’s obviously not possible to stream 1.5 Gbps into most viewers’ homes or to their mobile devices. The following chart provides approximate required bitrates to carry uncompressed digital video of different sizes (resolutions): Resolution Raw, uncompressed video carried over an HDMI, HD-SDI, or Ethernet cable requires a lot of bandwidth. Why do we need to compress video in the first place? In this post, I explain the concept of a Group of Pictures (GOP) which is used in most modern video encoding algorithms today, including MPEG-2, H.264, and H.265. In this Back to Basics series of blog posts, I revisit core and fundamental concepts in video compression and delivery and attempt to explain them in accessible, easy to understand ways. Sometimes in their daily lives, video engineers forget that not everybody understands the alphabet-soup of three letter acronyms (TLAs) that get used regularly in our industry.
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