Apple has been granted a patent (number 7,986,731) by the US Patent & Trademark Office for an H.264/AVC coder incorporating rate and quality controller.

A rate control system is disclosed for video coding applications. The rate controller assigns a quantization parameter for video data in a picture in response to complexity indicators indicative of spatial complexity, motion complexity and/or bits per pel of the picture.

A virtual buffer based quantizer parameter is proposed based on a virtual buffer fullness analysis and a target rate estimate, which is derived from the complexity indicators. A second quantizer parameter is proposed from a linear regression analysis of quantizer parameters used to code previously coded pictures of similar type (e.g., I pictures, P pictures or B pictures).

A coding policy decision unit defines a final quantizer parameter from a comparison of the two proposed quantizer parameters. The inventors are Barin Haskell, Adriana Dumitras, James Normile, Hsi-Jung Wu, Xiaochun Nie and Atul Puri.

— Dennis Sellers