Revisiting All-Zero Block Detection for Versatile Video Coding

The Versatile Video Coding (VVC) standard adopts a series of new coding tools in transform and quantization, including multiple transform selection, low-frequency non-separable transform, and trellis quantization. These new technologies, which bring significant coding gain, create daunting challenges to optimizing the VVC codec. In this work, we propose a new all-zero block (AZB) detection scheme tailored for VVC, with the collaboration of genuine all-zero block (GAZB) and pseudo all-zero block (PAZB) detection. First, to accommodate the multiple transform sizes in VVC, we develop a GAZB detection method that is apt for square and non-square residual blocks. Meanwhile, a theoretical upper bound is derived to locate the last significant coefficient and detect the potential frequency domain GAZB. Subsequently, a method tailored for trellis-coded quantization in VVC is devised for detecting PAZB. Finally, the GAZB and PAZB detection methods are collaboratively employed for AZB detection in VVC. The proposed method is implemented on the VVC codec Versatile Video Encoder (VVenC), and extensive experimental results show that the proposed method achieves promising time savings for test sequences of different resolutions with negligible rate-distortion performance loss.