Degradation mechanisms in multigeneration of MPEG compressed video

This paper describes mechanisms that cause degradation in multigeneration of MPEG compressed video. We present five mechanisms that contribute to the continued degradation in multigeneration: pixel domain quantization (PDQ), pixel domain clipping (PDC), compression control parameters variation (CCPV), motion vector re-estimation (MVR) and error propagation due to motion compensation (EPMC). Multigeneration error introduced by PDQ is larger for higher-bit-rate video. We observe that PDC affects mainly the DC coefficient. For CCPV, we notice that using the quantization scaling parameters of the first generation results in an increase in the average peak signal-to-noise ratio of lower-bit-rate video (compression ratio ≥ 6:1) while maintaining the specified target bit rate relatively constant. For MVR, multigeneration error is reduced when the motion vectors of the first generation are used for each subsequent generation. For EPMC, multigeneration errors in reference pictures propagate to frames that are predicted from them. Consequently, EPMC multiplies the effect of other mechanisms. It also results in error propagation between predicted frames from generation to generation.