Real-time digital video coding became a mandatory feature in current consumer electronic devices due to the popularization of video applications. However, efficiently encoding videos is an extremely processing/energy-demanding task, especially at high resolutions and frame rates. Thus, the limited energy resources and the dynamically varying system status (such as workload, battery level, user settings, etc.) require energy-efficient solutions capable to support run-time energy-quality scalability. In this work, we present an energy-quality scalable SAD Unit hardware architecture for the HEVC intra-frame prediction targeting real-time processing of UHD 8K (7680 × 4320) videos at 60 frames per second. Approximate computing is used to provide energy-quality scalability by employing configurable imprecise operators. The proposed Energy-Quality scalable architecture supports four operation points: precise computing, and 3-bit, 5-bit or 7-bit imprecision. When implemented in a 45-nm technology using Nangate standard cells library and running at 269 MHz, the proposed architecture consumes from 8.42 to 7.38 mJ to process each UHD 8K frame, according to the selected imprecision level. As a drawback, the coding efficiency (measured in BD rate) is reduced from 0.28 to 1.72%. Compared to the related works, this is the only intra-frame prediction SAD unit able to provide energy-quality scalability.
