Group of Pictures (GOP)
Definition
The periodic structure of I-frames, P-frames, and B-frames in a compressed video stream. Each encoding generation imposes its own GOP structure. When a video is re-encoded, the second encoder's I-frames may fall at positions that reveal the prior generation's GOP period.
Related terms
- DCT coefficient histogram
- A histogram of the discrete cosine transform coefficients across macroblocks or coding units in a frame or clip. After a single encode,...
- Double compression
- The condition in which a video has been encoded at least twice through a lossy codec. The term is also used loosely...
- I-frame (intra-coded frame)
- A video frame that is encoded entirely from its own pixel data, without reference to any other frame. I-frames mark the start...
- Inter-frame residual
- The pixel-level difference between a predicted frame and the actual frame after decoding. In unmodified video, residuals at scene cuts are elevated...
- Intra-refresh artefact
- The elevated count of intra-coded macroblocks or CTUs at frame positions that correspond to the I-frame interval of a previous encoding generation....
- Macroblock (MB) / Coding Tree Unit (CTU)
- The basic spatial coding unit: 16x16 pixels in H.264 (macroblock) and up to 64x64 pixels in H.265 (CTU). Each unit is classified...
- Motion vector consistency
- In unmodified video, motion vectors across consecutive frames track the same objects and follow smooth trajectories. A deleted or inserted frame breaks...
- P-frame (predictive frame)
- A frame encoded as a set of changes relative to a preceding reference frame. P-frames are smaller than I-frames because they only...
- Presentation Timestamp (PTS)
- A value stored in the container for each packet indicating when that frame should be displayed. In an unmodified recording, PTS values...
- Quantisation parameter (QP)
- A per-block or per-slice value that controls the coarseness of the DCT coefficient rounding step in H.264 and H.265. Higher QP means...
Explained in these topics
- Compression History Estimation in Video StreamsThe periodic structure of I-frames, P-frames, and B-frames in a compressed video stream. Each encoding generation imposes its own GOP structure. When a video i...
- Detecting Frame Deletion and Insertion in VideoThe repeating unit of inter-frame compressed video. A GOP begins with an I-frame (a complete image) followed by a fixed or near-fixed number of P-frames and B-...