Overview: Encoding and picture quality

Encoding quality depends on rate allocation, encoder effort and the picture changes introduced by compression.

The codec defines a format, but an encoder still chooses how to spend bits and computation on a particular sequence. Rate-control and preset choices influence that work. Artifact and metric topics then provide different ways to examine the result, including the effects of grain and repeated encoding.

• Rate control
  Rate control allocates encoded data under quality, bitrate or buffering objectives.

• Encoder presets
  Video encoder presets choose a bundle of coding decisions that trades encoding effort against compression efficiency.

• Quality changes and artifacts
  Compression artifacts, generation loss and grain describe different changes to the appearance of encoded pictures.

• Quality metrics
  Video quality metrics compare pictures through numerical models that measure particular kinds of difference.