group of pictures (GOP)
A file compression method that groups frames, or “pictures,” in encoded video to remove redundant frames. There are three GOP frame types: I-frames (intra-coded frames), P-frames (predictive frames), and B-frames (bidirectional predictive frames). These are collectively called a group of pictures (GOP). MPEG-2 and H.264 encoding in Compressor combine frames into groups of pictures during the encoding process to output a highly compressed file.
Important: When you apply an MPEG-2 preset to your source file, Compressor automatically assigns many of the preset’s properties (including the frame rate, which determines the “GOP structure” and “GOP size” properties) based on the properties of the source file. These automatically assigned properties are strongly recommended. However, if you’ve manually set the “Frame rate” property of the MPEG-2 preset, you can also set the values for the “GOP frame order” and “GOP size” controls.