Achieving re-loss-free video coding in a class of H.264 like hybrid coding

This paper presents some results on re-loss characteristics of multiple video compression cycles in H.264 like hybrid video coding. Ideally, when the same set of parameters is used, a video coding algorithm is desirable to be idempotent and re-loss-free (RLF) to multi-generation coding. This paper shows that H.264 coding may suffer severe re-loss during recompression using common encoding modes. The recompression mechanism is analyzed and a sufficient condition is presented for RLF hybrid coding. Two key methods, Prediction Mode and Q Identification (PMQI) and Preserving Q Clipping and Deblocking (PQC/PQD), are proposed to achieve general RLF coding. PQC is applied to H.264 and formulated into an integer linear programming problem. The H.264 transform and quantization are idempotent and using PMQI and PQC, H.264 can be modified to achieve RLF coding for some QP values. The modified H.264 RLF coding and the traditional H.264 coding have almost the same coding gain. Finally, the paper describes some future work on RLF coding.