How does Compression Work?
We’ll try to keep this as simple as we can. Video compression formats such as H.264 and MPEG-4 use a technique known as ‘difference coding’. What this does is try to compare the difference between the current video frame with the preceding frame to ensure that information which does not change (static background etc.) is not repeatedly transmitted. When encoding the video frames the encoder splits each video frame into specific types. These different types of frames are known as I-frames, P-frames and B-frames. Here is an example of a GOP (Group of Pictures) structure for video compression: GOP Structure for H.264/MPEG-4 I-frame: An intra-frame, or I-frame, is a video frame which has been encoded without any reference to any other frame. A video file will always start with an I-frame and will have subsequent I-frames added at regular intervals. I-frames are also known as key-frames or access points and are important for random access of video files such as rewind, fast-forward and seek
