Emulating short MPEG GOPs with less I-frames

Frequent placement of intra-encoded pictures (I-frames) in MPEG video facilitates (1) error resilience over lossy network transmission and (2) random access for VCR functionality. However, high I-frame frequency sacrifices quality-to-bitrate efficiency that can be gained by using longer sequences of inter-encoded pictures. We present a simple strategy that emulates frequent I-frame encoding (short GOPs) while using fewer I-frames. Our approach maintains a small set of previously encoded/decoded I-frames that can be re-used to start future GOPs. A least-recently-used (LRU) policy is used to maintain this set of I-frames. We demonstrate that this strategy allows gains in PSNR for constant bit rate encoding while providing the benefits of frequent I-frame placement.