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.
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