H.264 hierarchical P coding in the context of ultra-low delay, low complexity applications

Despite the attention that hierarchical B picture coding has received, little attention has been given to a related technique called hierarchical P picture coding. P picture only coding without reverse prediction is necessary in constrained bit rate applications that require ultra-low delay and/or low complexity, such as videoconferencing. Such systems, however, have been using the traditional IPPP picture coding structure almost exclusively. In this paper, we investigate the use of hierarchical P coding vs. traditional IPPP coding and demonstrate that it has significant advantages which have not yet been well documented or understood. From a pure coding efficiency point of view, we show that for encoders configured to use ultra-low delay and low complexity coding tools, hierarchical P coding achieves an average advantage of 7.86% BD-rate and 0.34 dB BD-SNR.