Fast First Pass in Two-Pass Video Encoding Using Sub-Sampling

Rate control (RC), specifically two-pass, is the main operation mode in VVenC, an open and optimized Versatile Video Coding (VVC) encoder. VVC offers substantial bitrate savings over its predecessor, High Efficiency Video Coding (HEVC), at the price of increased complexity. This complexity increase is apparent in both encoding passes of VVenC. While the complexity redaction in the final pass has been discussed, this paper considers complexity reduction in the first pass, in addition to its already reduced search space. To reduce the overall runtime of a two-pass RC method, spatial and temporal sub-sampling of the first encoding pass is proposed. The experimental results show that the proposed first-pass sub-sampling in two-pass RC can speed up the encoding process of the default two-pass rate control algorithm in VVenC by 18%, with 0.48% loss in coding efficiency, when using the faster preset. Using temporal sub-sampling for the look-ahead, one-pass RC in VVenC can achieve time savings of 11% for bit-rate increases of 0.28%.