Rate-distortion analysis and streaming of SP and SI frames

Abstract

The new SP and SI picture types, introduced in the latest video coding standard H.264, allow drift-free bitstream switching and can also be used for error-resilience and random access. In this paper, we propose a model for the rate-distortion performance of SP and SI pictures and compare it to experimental results, obtained with our implementation of an SP/SI encoder, made publicly available and recently adopted by the Joint Video Team. The model predicts how the relative sizes of SP and SI slices can be traded off. We analyze, both theoretically and experimentally, how this can be used to minimize the transmitted bit rate when SP frames are used for video streaming with packet losses and derive optimal settings for our encoder. We investigate the benefits of SI and SP frames for error resilience as compared with periodic I frame insertion. Empirical rate-distortion curves predict rate-distortion gains may be obtained. Experiments carried out over a simulated throughput-limited network confirm this to be the case when the end-to-end delay is limited. We analyze the influence of loss rate and delay on the congestion-rate-distortion performance of streaming with SI and SP frames. Our results identify scenarios for which SI and SP frames provide an attractive alternative to streaming with I frames.