Overview: Picture prediction and random access

Picture prediction creates dependencies that determine how video can start decoding at a requested point.

Seeking to a picture and beginning to decode there are different operations. A predicted picture may need earlier reference information, so a useful access point has to satisfy the codec's dependency rules. Intra coding, keyframes, groups of pictures and reference frames explain how that starting point is built.

• Intra-frame compression
  Intra-frame compression represents a picture using information from within that picture rather than other pictures.

• Inter-frame prediction
  Inter-frame prediction reconstructs a picture using previously decoded reference pictures and coded corrections.

• Keyframes and random access
  A video random-access point lets decoding begin without reconstructing the whole preceding stream.

• Groups of pictures (GOPs)
  A group of pictures describes a sequence of coded pictures and their prediction relationships around access points.

• Reference frames
  Reference frames are decoded pictures retained so that other pictures can use them for prediction.